Natural Hazards and the Mitigation of their Impact 3031072251, 9783031072253

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Gábor Mezősi

Natural Hazards and the Mitigation of their Impact

Natural Hazards and the Mitigation of their Impact

Gábor Mez˝osi

Natural Hazards and the Mitigation of their Impact

Gábor Mez˝osi Department of Geoinformatics, Physical and Environmental Geography University of Szeged Szeged, Hungary

ISBN 978-3-031-07225-3 ISBN 978-3-031-07226-0 (eBook) https://doi.org/10.1007/978-3-031-07226-0 Translation from the Hungarian language edition: “Természeti Veszélyek és Hatásaik Csökkentése” by Gábor Mez˝osi, © Mez˝osi Gábor, 2021. Published by Akadémiai Kiadó. All Rights Reserved. © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2022, corrected publication 2022 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Preface

Writing a book with a new perspective on natural hazards is not an easy task because; in recent years, there have been lots of works in this title and theme, highlighting these situations that are worsening globally. Without the presence of man, these conditions would not be understood as threats since the problems and conflicts they cause are primarily understood from the human perspective. Without the presence and involvement of humans (in a broader sense, the living world), droughts, earthquakes and flash floods do not pose a threat. Population growth often increases the number of people potentially affected by these hazards, while the financial damage is also dynamically increasing in close correlation. In many cases, population growth and vulnerability to natural hazards show a similar upward trajectory, but the larger population can mitigate these adverse processes. Therefore, it is understandable that the fundamental objective concerning natural hazards is to reduce their adverse, harmful effects. Therefore, the primary message of this book is to show that reducing adverse impacts is not only a desirable goal but, in many cases, an achievable one. For this reason, the primary aim of this book is to present steps that can be taken to mitigate and prevent impacts. In the text, the reader will also find a professional summary of the most important relevant events, on a scale appropriate to the events, which can help prevent hazards and reduce the extent of impacts. From this point of view, an essential element of the message is to show that the scientific analysis of the issues can help manage and forecast hazards. The present compilation can be split into two major parts. The shorter first part summarises the general professional, theoretical (e.g. physical basis of hazards, consequences of impacts) and practical (e.g. management, professional organisational framework) issues of natural hazards from a comprehensive global perspective. The second part analyses natural hazards separately. The analysis follows a consistent logical sequence, first presenting the parameters involved in creating the processes and their interrelationships. The parameters and the monitoring of the emergence of the hazard are followed by an evaluation and methodology of their development and consequences and then a description of their effects. Finally, a brief analysis of the socio-professional responses to these impacts and the likely direction of future change is presented in each case. v

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Usually, when a reader is given an overview of work on natural hazards, it soon becomes clear on what basis and with what professional background it was written. For example, some volumes focus on analysing geophysical natural hazards (e.g. earthquakes, volcanic activity), others on floods and flash floods. Thus, hazards can also be examined from a geological, hydrological, meteorological or social science perspective, analysing the detailed physical, chemical, financial, social, etc., scientific background of each hazard from this perspective. Other books analyse the financial management of natural hazards, the damage caused by disasters or even the technical steps to mitigate the hazard process. In addition to being professionally sound, two important technical aspects had to be considered in the preparation of the book. First, the need for a synthesis approach, whereby the text shows that these phenomena appear partly as a combination of the natural hazards and their effects analysed and partly as a combination of the mitigation efforts intended for and by society. It is not the case that all natural hazards can be accurately predicted and their impact reduced. Still, even in the case of earthquakes, for example, it is important to take protective action at all stages of the phenomenon (even if the human activity may trigger a hazard process). In other words, both before and after the event, human intervention (e.g. preparatory, alert, mitigation, reconstruction and other management tasks) has a significant role to play. This work aims to contribute to a complex approach to these issues. Thus, the volume structure is rather simple: it aims to provide a comprehensive synthesis of the processes that occur, the adverse effects that often arise and the mitigation issues. Another aspect is the issue of digitalisation. The target group aimed not primarily to produce e-learning-based learning material but to provide as many aspects of basic professional knowledge as possible, based on which independent problem-solving could be achieved. To help achieve this, most of the material incorporated in the text is available digitally. A list of databases that are worth using to analyse and assess natural hazards is also presented in a summarised form. The compilation was motivated by three factors: – a systematic analysis of the natural, social and economic consequences of natural hazards can help to manage the process professionally, – the application of scientific and management knowledge, the social and economic impact/damage caused by the hazard can be reduced, – based on scientific and management information, institutional and societal decisions can be prepared. The target audience for this work is university students, academics, professionals and decision-makers involved in natural hazards. Although the compilation covers essentially all phenomena that can be included in natural hazards, it is not a global work but rather a regional one. Thus, it does not deal with all hazards in the same detail but focuses on those hazards that occur in the warm-temperate and arid areas according to Köppen’s climate classification, i.e. Europe, parts of Eurasia, and the region from Vietnam, through Russia and the Middle East (e.g. floods, earthquakes, tropical cyclones, droughts, mass movements). Therefore, the focus of the compilation is mainly on natural hazards in the core regions of Eurasia, with less detail

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on hazards related to, for example, seas (and their coasts) and volcanoes. The first chapter analyses general issues related to natural hazards on a global scale and their mitigation options. A more detailed discussion of individual hazards can be found in the subsequent chapters. It is often asked what justifies such a compilation. If we look at the data on a global scale (e.g. https://ourworldindata.org/causes-of-death), we can see that natural hazards cause an average of 60,000 casualties per year and are responsible for 0.4– 0.5% of GDP loss, according to reinsurer Munich Re. These figures, especially the first one, which is below 0. % of the affected population, do not seem significant, but it is precisely the increasing anthropogenic impact that has made this low level of mortality possible. The current figure of millions of victims of the COVID19 pandemic (in September 2020) suggests otherwise, of course. With the right knowledge and preparations, it is possible to reduce the very wide-ranging impact of natural hazards and slow the exponential increase in financial damage, which is why addressing this issue. Chapter 5 of the book, Biosphere-Releated Natural Hazards, is by Dr. Tímea Kiss (University of Szeged) and Chap. 6, Extraterrestrial Hazards, is by Dr. Róbert Géczi (Budapest, VERITAS Research Institute). The book was edited by associate professors Tímea Kiss (SZTE) and Szabolcs Ákos Fábián (PTE), who, in addition to their academic and departmental duties, did a very conscientious job. I want to take this opportunity to express my appreciation to them for their work. Their comments and corrections have been used in the compilation. Szeged, Hungary October 2020

Gábor Mez˝osi

Contents

1 General Analysis of Natural Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Natural Hazards and Their Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.2 Interpretation and Definitions of Natural Hazards . . . . . . . . . . . . . . . 1.3 Overall Impacts and Consequences of Natural Hazards in Numbers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3.1 Human Aspects of Natural Hazards and Disasters . . . . . . . . 1.3.2 Economic Aspects of Natural Hazards and Disasters . . . . . 1.4 Logical Steps for Reducing the Impacts of Natural Hazards . . . . . . . 1.4.1 Early Warning Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5 Management of Natural Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 Geophysical Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1 Natural Hazards Posed by Volcanic Activity and Mitigation Options . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.1 The Formation and Spatial Distribution of Volcanoes . . . . . 2.1.2 The Intensity of Volcanic Activity . . . . . . . . . . . . . . . . . . . . . 2.1.3 Consequences of Volcanic Activity and Related Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.4 Relationship of Volcanism to Other Natural Hazards . . . . . 2.1.5 Forecasting and Mitigating Volcanic Hazards . . . . . . . . . . . 2.1.6 Monitoring Volcanic Activity . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.7 Issues Related to Forecasting Volcanic Eruptions . . . . . . . . 2.1.8 Technical Tasks Related to Reducing Volcanic Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.9 Human Tasks Tackling to Mitigate the Impact of the Hazard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 The Earthquake Hazard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.1 Naturally Occurring Earthquakes and Their Spatial Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

1 1 9 11 15 16 23 24 25 30 35 35 36 39 41 48 49 49 51 52 52 53 53

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2.2.2

Measuring the Location and Magnitude of an Earthquake Epicentre . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.3 The Frequency of Earthquakes and Their Regional Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.4 Impacts of Earthquakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.5 Mitigating the Impacts of Earthquakes and Responding to Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.6 Some Infrastructural Aspects of Mitigating Earthquake Impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 The Tsunami Hazard—Seismic Sea Waves . . . . . . . . . . . . . . . . . . . . . 2.3.1 Tsunami Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.2 Hydrometric Characteristics and Movement of a Tsunami . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3 Consequences of a Tsunami, Environmental and Social Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.4 Mitigation Options for the Effects of Tsunamis . . . . . . . . . . 2.4 Natural Hazards Caused by Landslides, Mass Movements . . . . . . . . 2.4.1 Some Types of Landslides . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.2 Physical Background of Mass Movements . . . . . . . . . . . . . . 2.4.3 Causes of Mass Movements . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.4 Spatial Occurrence of Mass Movements . . . . . . . . . . . . . . . . 2.4.5 Consequences of Mass Movements . . . . . . . . . . . . . . . . . . . . 2.4.6 Hazard Mitigation and Some Issues of Protection . . . . . . . . 2.4.7 Initial State, Monitoring and Mapping of the Process . . . . . 2.4.8 Mass Movement Prediction . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.9 Some Elements of Protection Against the Effects of Mass Movements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.10 Communicating the Hazards Associated with Mass Movements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Meteorological Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Extreme Meteorological Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.1 Heatwaves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.2 Cold Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.3 Fog Hazard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Tropical and Temperate Cyclones and Related Phenomena, Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.1 Tropical Cyclones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2 Main Characteristics of Hurricanes and Typhoons . . . . . . . 3.2.3 Temperate Cyclones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Extreme Climatic Phenomena Associated with Convective (Vertically Mixing) Air Mass Movement . . . . . . . . . . . . . . . . . . . . . . . 3.3.1 Thunderstorms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.2 Lightning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

56 58 60 62 68 69 69 72 74 75 77 78 80 81 83 84 87 87 89 90 91 91 97 97 98 106 108 110 110 111 115 117 117 118

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3.3.3

Extreme Rain, Freezing Rain, Snow, Blizzards and Snowstorms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.4 Tornadoes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.5 Dust and Sandstorms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 Mapping and Forecasting Extreme Weather Events . . . . . . . . . . . . . . Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Hydrological Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 Flood Risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.1 Definition, Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.2 Parameters Used in Flood Analysis . . . . . . . . . . . . . . . . . . . . 4.1.3 Types and Spatial Aspects of Floods . . . . . . . . . . . . . . . . . . . 4.1.4 Some Natural and Social Consequences of Floods . . . . . . . 4.1.5 Physical Consequences of Floods, Riverbed Formation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.6 Flood (Risk) Management and Mitigation . . . . . . . . . . . . . . 4.1.7 Expected Trends in Flood Risk . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Flash Floods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1 Spatial and Temporal Characteristics of Flash Floods . . . . . 4.2.2 Effects of Flash Floods and the Damage They Cause . . . . . 4.2.3 Estimation of Flash Flood Risk . . . . . . . . . . . . . . . . . . . . . . . 4.2.4 Protection, Mitigation and Adaptation Strategies . . . . . . . . 4.3 Inland Excess Water Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.1 General Characterisation, Types . . . . . . . . . . . . . . . . . . . . . . . 4.3.2 Factors Influencing the Formation of Inland Excess Water, Measurement and Extent of Inland Excess Water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.3 Environmental Consequences of Inland Excess Water . . . . 4.3.4 Treatment and Management of Inland Excess Water . . . . . . 4.4 The Environmental Risk of Drought and Some of Its Management Issues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.1 General Characterisation, Drought Types . . . . . . . . . . . . . . . 4.4.2 Factors and Measurement of Drought . . . . . . . . . . . . . . . . . . 4.4.3 The Environmental Effects of Drought . . . . . . . . . . . . . . . . . 4.4.4 Drought Management Questions—Effects and Answers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Soil Erosion Caused by Water and Wind . . . . . . . . . . . . . . . . . . . . . . . 4.5.1 Definition of Soil Erosion and Its Determinants . . . . . . . . . 4.5.2 Types of Soil Erosion and Its Spatial Aspects . . . . . . . . . . . 4.5.3 Calculating the Extent of Soil Erosion by Precipitation and by Wind . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.4 Some Consequences of Soil Erosion Caused by Water and Wind . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.5 Answering Some Management Questions on Soil Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

120 124 126 131 133 137 137 137 138 141 145 147 147 151 153 154 155 157 159 161 161

162 167 167 169 169 171 178 181 186 186 187 190 200 202

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4.5.6 Future Changes in the Extent of Soil Erosion . . . . . . . . . . . . 202 Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 204 5 Biosphere-Related Natural Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tímea Kiss 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Human Health Epidemics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 Plant and Animal Health Epidemics . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4 Rapid Spread of Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.1 Emergence of Invasive Species . . . . . . . . . . . . . . . . . . . . . . . . 5.4.2 Algal Bloom . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4.3 Insect Invasions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5 Ecosystem Changes and Degradation . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5.1 Consequences of Fires Affecting Vegetation . . . . . . . . . . . . 5.5.2 Forest Degradation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.5.3 Extinction of Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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6 Extraterrestrial Hazards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Róbert Géczi 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1.1 Cosmic Objects Related to the (Hazard) Process . . . . . . . . . 6.2 Physical Background and Results of the Impact Process . . . . . . . . . . 6.3 Consequences of Extraterrestrial Effects . . . . . . . . . . . . . . . . . . . . . . . 6.4 Mitigation Options Concerning the Impact of the Hazard . . . . . . . . . Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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7 Climate Change and Its Impacts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 Physical Background and Trends in Climate Change . . . . . . . . . . . . . 7.3 Some Causes and Consequences of Climate Change . . . . . . . . . . . . . 7.4 Impact of Climate Change on Inland Ice Sheets, Glaciers and Oceans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.5 Some Options to Mitigate the Impacts of Climate Change . . . . . . . . Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

241 241 241 246

Correction to: Natural Hazards and the Mitigation of their Impact . . . . .

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Chapter 1

General Analysis of Natural Hazards

Abstract The chapter provides a comprehensive overview of natural hazards but does not cover man-made hazards. From a theoretical point of view, it analyses the relationship between natural hazards and risks, the physical basis for the development of hazards and the consequences of their effects. It also quantifies the human and financial aspects of hazards on a global scale. On average, natural hazards cause 60,000 deaths per year and are responsible for 0.4–0.5% of GDP loss on this scale. These figures may not seem significant, but the increasing anthropogenic impact has made the low mortality levels possible. The chapter also briefly summarises some of the practical issues associated with hazards, e.g. management issues. That is, to what extent the consequences of hazards can be reduced in the preparation, mitigation or reconstruction phase.

1.1 Natural Hazards and Their Types In recent decades, an increasingly common concern has been the emergence of different types of damage inflicted by natural disasters, which affect people’s daily lives and economic conditions. These types of damage are often attributed to the effects of natural hazards such as volcanic eruptions, earthquakes, droughts and a lot more. The general concept of natural hazards refers to unusual and extreme events which can cause severe ecological and economic damage. These effects may relate to human life, health, property damage, social and economic disturbances and environmental disturbances (UNISDR, 2009a). Although there is a definition of an intense hazard, i.e. a disaster, from UNISDR (the United Nations Disaster Reduction Strategy), it is not universally accepted or widespread. According to this definition, a disaster occurs when, because of a natural hazard the death toll is over ten or one hundred or more people are affected, or a state of emergency is declared, or international assistance is required. Regardless of whether or not the number of these harmful threats is increasing, it is certain that due to the increasing communication possibilities, more and more widespread media, population growth, or better health and financial status, people are more sensitive to these effects. Natural hazards always appear as an interaction between these extreme events and human existence. That is, © The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 G. Mez˝osi, Natural Hazards and the Mitigation of their Impact, https://doi.org/10.1007/978-3-031-07226-0_1

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2

1 General Analysis of Natural Hazards

they are difficult to interpret independently of the living environment. As a result, some people distinguish between potential and actual dangers (Montz et al., 2017). All of these also mean that knowledge of the functioning of the system seems to be more important than natural elements themselves when managing natural hazards. Natural hazards can be categorised in a few ways. One kind of categorisation is based on the range of key influencing factors that determine the type of the emerging hazard. Certain natural hazard types are often caused by the interaction of several factors, e.g. the type of drought is mainly determined by different temperatures, precipitation and soil cover parameters. However, the number of influencing factors causing an earthquake or a volcanic eruption is lower regarding this type of categorisation. Moreover, we also have to consider social factors that often play a crucial role in unexpected hazards, such as an earthquake. A good example of this is the 2010 earthquake in Haiti, which claimed more than 100,000 victims, as opposed to the 63 deaths of the slightly stronger 1989 San Francisco earthquake. One of the keys influencing factors of the Haitian earthquake must have been a social or a society-related one, for example, the poorly built houses and the poverty-stricken population that was not prepared for a hazard of this magnitude (Keller & DeVecchio, 2016). Based on the above, natural hazards can be distinguished as meteorological, hydrographic, geophysical, biological, environmental, technological and social hazards (Table 1.1). The last category might seem to be strange here, though the natural hazard appears as an interaction between the environment and the human sphere. Although human activity does not increase the occurrence of certain hazards (contrary to the opinion of Montz et al., 2017), it can certainly enhance the occurrence of sociological hazards (Cutter et al., 2003; Zlateva et al., 2011). A good example of measuring this type of hazard is the social vulnerability index (Flanagan et al., 2011). The effects of technology and technical hazards affect natural elements and are therefore listed. In 2018, according to Munich Re Reinsurance, these hazards and disasters claimed more than 10,000 casualties, one-third of which were due to geophysical hazards, the second-third of the casualties were caused by floods, and one-quarter of the victims were inflicted by meteorological events. Only 10% of deaths are linked to other natural hazards. The insurance company estimated the financial damage caused by natural disasters at 160 billion USD (only half was insured). 70–90% of the damage was attributed to meteorological and hydrological hazards and about 10% to geophysical-type hazards (MURe, 2018). It can be seen that lots of surfaces and underground events, which are mainly of natural origin, can cause very serious damage to human life and wildlife in general. The EM-DAT database (https://www.emdat.be) reflects the increase in the number of reported natural hazards in recent decades. The keyword is “reported risks”, the number of which has changed significantly, which is also partly due to the improving information system. The numerical increase of meteorological and hydrological hazards can be seen here; the dynamic increase of the related costs exhibits a realistic picture (Table 1.2). These events (such as earthquakes, windstorms and drought) always galvanise society into action. However, once the danger has passed, there is usually a muted recovery, although reducing the effects of the threats requires continuous action.

1.1 Natural Hazards and Their Types

3

Acknowledging the importance of threats has prompted action in numerous directions, both at regional and global levels; for example, a lot of model results have been produced. Several models can provide a more precise and well-established picture of global temperature predictions (NASA, 2005). Concerning windstorm hazards, another good example at the global level is a model that can forecast the development Table 1.1 Classification of natural hazards (Gebhardt et al., 2017; ISDR, 2004) Natural hazards Hazards caused by meteorological (climatological) reasons Natural processes or phenomena in the atmosphere

– Tropical whirlwinds (hurricanes, typhoons) – Tropical, temperate cyclones – Windstorms, dust storms, tornadoes, wind erosion – Hail, freezing rain, snowstorms – Extreme precipitation, extreme temperature – Atmospheric cold, warm wave, lightning – Fog, forest fire

Hydrological hazards – Floods The natural processes or the phenomena of the – Flash floods hydrosphere and the cryosphere – Drought – Inland excess water – Soil erosion (by water, by wind is also presented here), coast erosion – Melting of permafrost – Mass movements on a slope (wet environment—e.g. avalanches, rock flows) Geophysical hazards The natural geological, geomorphological processes or phenomena of the crust

– – – –

Earthquakes Volcanic eruptions Tsunami Slope mass movements (dry environment)

Biological hazards

– – – – –

Animal and plant diseases Epidemics Forest fires Harmful overgrowth of insects and pests Locust swarms

Environmental hazards

– Due to intensive human land use, natural resources are damaged, and the natural processes of the ecosystem change in a negative direction – Decreasing biodiversity – The frequency and intensity of numerous environmental hazards change in a negative direction, resulting in, e.g. soil erosion, soil degradation – Increasing soil, water and air pollution, etc.

Extraterrestrial hazards

– Meteorite falls – Solar wind (continued)

4

1 General Analysis of Natural Hazards

Table 1.1 (continued) Man-made hazardsa Technical, technological hazards

– Technological, industrial accidents – Infrastructure damage – Industrial pollution, e.g. radioactive contamination, industrial accidents, toxic waste, dam failures, oil contamination, fires, etc.

Hazard from social causes

– Social vulnerability, resilience – Social cohesion

a These are often referred to as man-made hazards, but it is also reasonable to include society-related

hazards. A lot of researchers also include economic threats in this category. Blasts, terrorism or cyber-attacks can also be included in this group, but we focus on natural hazards (which, as we will see, are not homogeneous categories) in the discussion

Table 1.2 Over the past 35 years, the number of hazards and their financial damage has been increasing Period

Drought Number of reported events

Amount of damage (billions of USD)

Earthquake

Flood

Number of reported events

Number of reported events

Amount of damage (billions of USD)

Storm Amount of damage (billions of USD)

Number of reported events

Amount of damage (billions of USD)

1980–1982 50

10

50

40

130

10

150

10

1983–1985 50

10

50

10

160

25

180

20

1986–1988 45

5

60

20

200

30

180

20

1989–1991 45

10

80

30

180

35

270

50

1992–1994 40

20

60

40

230

50

250

50

1995–1997 40

10

70

40

280

80

240

40

1998–2000 75

20

100

50

350

100

270

70

2001–2003 70

15

110

30

480

80

300

50

2004–2006 50

10

100

50

520

40

320

300

2007–2009 60

10

50

100

540

50

300

110

2010–2012 70

45

80

300

470

120

350

170

2013–2015 70

30

70

30

400

100

330

130

Source CRED (2015) and EMDAT (2019)

and possible path of hurricanes 5–6 days in advance (Hurricane, 2019). The European Drought Observatory (EDO, 2014) or the American system is good examples for forecasting drought, though they have different spatial and timescales (Wilhite et al., 2007). Several organisations and associations have made serious commitments to mitigate the damage caused by natural hazards both on regional and global scales. The Sendai Framework for Disaster Risk Reduction (Sendai, 2015) was the first

1.1 Natural Hazards and Their Types

5

major agreement of the UN Member States to reduce the damage caused by natural disasters, such as earthquakes and floods, by 2015–2030. The agreement sets out goals and priorities (Disaster Risk Reduction—DRR), the first of which explains why it is important to define and understand disaster risks, their magnitude, the number of people exposed to disasters, the nature of the threat and the management issues related to mitigation (Sendai, 2015). This compilation aims to help understand the key issues, relationships and effects. Not all hazards are known in every detail; as a result, their exact course, the number of people possibly affected, their area, probability of occurrence, course and effects cannot be precisely determined. Individual processes are often not even considered a hazard because their criteria only partially meet the hazard/disaster criteria (e.g. soil erosion). These events often do not endanger human life, but their trends are well known due to other relevant and supplementary data (e.g. new data collection methods, socio-economic data—Cutter et al., 2003). Natural hazards are sometimes interrelated depending on their scale, but they are always spatial and temporal events, even in themselves. Therefore, it is understandable that there are classifications that group the hazards according to time and space. Table 1.3 shows the very different speeds, spatial extent and dynamics of some typical processes. The overview presented in the table does indeed indicate that these processes can be rapid (e.g. hail) or slow (e.g. drought), and they can have Table 1.3 Duration and some other parameters of the process of natural hazards (after Alexander, 1993) Type of hazard

Duration of hazard

Frequency of hazard

Range of hazard

An avalanche of snow and debris

s–min

Is associated with the frequency of heavy rainfall

0.1 ~ 3–5 km2

Earthquake

s–min

Depends on its magnitude, it Depends on its can be many hundreds magnitude—km2 —10 km2 smaller each day

Tornado

min–h

Annual—seasonal

Close to local

Hurricane

h–days

Annual—seasonal

Along hurricane routes—thousand km2

Hail

min

Shifting to early summer, it follows the frequency of thunderstorms

Local ~ 0.01 km2

Slope mass movement (dry)

s–months

Precipitation supply

Defined by orographic, lithological factors and types of movement

Volcanic eruption

h–years

Daily—Stromboli, thousands of years—e.g. Yellowstone

0.1 ~ 25 km2

Soil erosion

h–decades

Continuous

0.01–1 million km2

Drought

day–years

For a large area 2–3 years

10–1 million km2

6

1 General Analysis of Natural Hazards

an enduring effect. The present volume analyses these issues in more detail in the chapters on each hazard. The table also informs us that the duration, frequency and range of these processes can be very different, so they can also be classified on a timescale. The number of natural hazards in a given area is presented in the upcoming sections and chapters. We focus on whether there is a historical change in the number or severity of these hazards. In everyday communication, an increase in the number of hazards is often mentioned, and it can be because all climate models indicate an increase in the number of extreme temperature values and precipitation intensity. Thus, given that almost two-thirds of the natural hazards are of meteorological and hydrological origin, it is quite understandable. Moreover, it can also be explained by the significantly improving flow of spatial and regional information and the growing population. However, the number of geophysical hazards (earthquake, volcanism), which usually have a lot of casualties, does not show such a trend-like increase in numbers, and by their very nature, such an estimate is not possible to be made. This question will be explored in more detail later, but to sum up, the occurrence of all events is indeed increasing (for the reasons given above), which is mainly explained by an increase in the number of (hazardous) hydrological and meteorological events (Fig. 1.1). Historically, the dangers that led to disasters have been documented. Such a slowmoving process was the drought in the tenth and eleventh centuries, then later in the

Fig. 1.1 Increasing number of natural hazards and disasters can be attributed to both hydrological and meteorological causes, the rapidly expanding information network and dynamic population growth. At the same time, the susceptibility of the population to natural hazards has increased. Source EMDAT (2019)

1.1 Natural Hazards and Their Types

7

sixteenth century in Mexico. These droughts led to a decline in agricultural productivity and then to the general disintegration of the Mayan system. Numerous social processes (such as increased food demand due to population growth) also played a role in the emergence of such changes, but drought was undoubtedly the most important element. It is also difficult to determine the temporal changes of the hazards, and their possible increasing or decreasing frequency, because no instrumental data were available to validate the events themselves. Measurements related to droughts started to be taken about 150 years ago (Brázdil et al., 2018). (Of course, there was a limited social need for that at the time.) Although proxy data can be used to estimate the frequency and characteristics of the occurrence of these threats, even the length of the data series used for research determines the outcomes, and data series with different lengths provide different results (Toonen, 2015). On a local scale, the temporal changes of this natural hazard and the long-term responses are well illustrated by the adaptation to the ebb and flow of Fert˝o Lake in the north-eastern part of the Carpathian Basin. In times of floods, buildings were built higher and farther than the contemporary lakebed, while in low-water times, buildings also moved closer to the lake (Kiss, 2005). The number of environmental disasters reported to insurance companies or international monitoring databases (e.g. EMDAT, 2019; UNISDR, 2009b) has increased since 1970. As indicated in Fig. 1.1, it is in line with better access to information and easier access to the media since 1970. It should be noted that these data were mostly derived from observations (and not measurements). However, the number of these events increased while the number of geophysical events remained stable. The fact that the number of tectonic events is scarcely changing and that the number of climatic events, and the often-related hydrological events, are increasing is also a cause for concern about the impact of climate change on the magnitude of natural hazards (Peduzzi & Herold, 2005). Observational data show that the magnitude of climate extremes has changed since 1950, mainly due to the human impact on the climate system (IPCC, 2012, 2014). It is generally true that, according to this line of thought, it is difficult to predict the number and magnitude of hazards in the future due to the plentiful factors that control the system and the often-stochastic uncertainties of these risks and disasters. Climate change and the natural and environmental hazards associated with it can be forecast better, as an increase in intensity (e.g. the larger number of more extreme events) can be anticipated here. However, there are easily identifiable and essential connections of the spatial and territorial extent of natural hazards. For example, the potential locations of geophysical hazards, such as volcanism and/or earthquakes, can be located along the plate boundaries of the microcontinents or along spreading ridges in advance; the occasionally changing trajectory of major storms can also be predicted. Tropical cyclones mainly affect coastal areas, but dust storms are typical of sub-Saharan areas. In general, it can be said that extreme geophysical and meteorological events usually have well-determinable spatial extent and involvement. It cannot always be calculated accurately; for example, prolonged drought periods affecting more than 500,000 km2 (they occur 6–8 times a year globally) cannot be precisely delineated

8

1 General Analysis of Natural Hazards

(Sheffield et al., 2009). However, a hazard of higher intensity (e.g. stronger earthquakes, greater droughts) affects a larger area. The size of the affected areas can be calculated well in some cases (e.g. earthquakes). The duration and the extent of natural hazards depend significantly on the scale of the event (Table 1.2). Concerning spatiality, hazards are classified in different scales depending on their types. On a global scale, some calculations examine the area’s exposure to natural hazards, the vulnerability of the environment and the susceptibility and social parameters associated with the hazard. The latter of these, such as social risk assessment, is quantified based on the degree of the adaptability and buffering capacity of the environment (WRR, 2017). Of these, the global values provided for more than 170 countries are indicated by parameters that reveal the extent to which a certain area is exposed to natural hazards and their effects. It reveals that the first 100 countries on this unpleasant list are hardly any European ones (Romania is the 97th, and Hungary is the 104th—both mainly due to exposure to natural hazards). The first places in this WRR—World Risk Report 2016—are occupied by Oceania, the Indonesian islands and Central American countries similarly due to natural hazards. Hazards can become interlinked due to their temporal and spatial appearance, but this is strongly dependent on their scale. A historical-scale analysis of natural hazards shows that all major hazards were local (often their occurrence) due to limited information flow. This statement is also true “backwards”. The same degree of danger was considered local in the early Middle Ages, regional in the nineteenth century, and is possibly considered severe and affecting a large area nowadays. The Munich Reinsurance data (Fig. 1.2) display the identified natural hazards on a local–regional scale and not globally (MURe,

Fig. 1.2 Geographical distribution of different types of natural hazards in 2014. Source MunichRe (2014)

1.2 Interpretation and Definitions of Natural Hazards

9

2019). On the one hand, it can be deduced from the compilation based on the data and experience of the insurance company that not all hazards appear in the traditional categorisation. On the other hand, only threats for which damage claim had been put in were entered into the system (it must also be noted that about half of the known threats have insurance cover). Two statements shall be emphasised based on what has been said so far: first, natural hazards cannot be interpreted without human existence. Desert drought without human susceptibility cannot be interpreted as a danger, nor can a strong earthquake be affecting an uninhabited area. In this system of danger and the effect it evokes, it is difficult exactly to determine what is more important because neither the place nor the process itself is the only component of the formation and effect of the hazard. That is, it is not the location alone that determines vulnerability. In this case, not only the concentration of dangers, their speed and the extent of those affected must be considered, but also the preparation from the social side, the reduction of vulnerability and so on. It is also worth noting that not all extreme natural processes pose a natural threat. In many cases, floods can positively affect the condition of an area and its inhabitants (e.g. the ancient Nile). At the same time, major floods can also have a devastating effect (e.g. Bangladesh in 1991). Looking at natural hazards on a historical scale, regardless of their measurable severity, the annual frequency of events with numbers of casualties (e.g. hurricanes, earthquakes, floods) has not changed significantly at the end of the last century (Douglas et al., 1996). However, present-day data are much more nuanced because most data show an increase in the number of hazards (not those with a really large number of victims).

1.2 Interpretation and Definitions of Natural Hazards In everyday use, the concepts of danger, risk, disaster, vulnerability or susceptibility are often used synonymously with each other. However, these concepts are not the same categories; some differences can clearly define on a professional basis. Several competent bodies have tried to define these concepts, but it cannot be said that there is a generally accepted definition. This definition may not be very necessary for everyday use, but it is important to clarify their use in terms of content. This information is important for some companies (e.g. insurers), and the proper definition application is necessary for protection and forecasting. The most common definition is that a natural hazard is a natural process or phenomenon that causes life-threatening injuries or other adverse health effects, as well as damage to social, economic or environmental damage to assets (UNISDR, 2009a). The natural hazards presented in Table 1.1 are, as can be seen, broken down into natural and man-made hazards. However, there is no common definition of natural/environmental hazards; its definition depends on who refers to this concept. For example, drought can be defined in terms of hydrology, agriculture, energy and tourism, and according to the different aspects, the definitions will be slightly

10

1 General Analysis of Natural Hazards

different. We know of numerous processes that can be interpreted as hazards, and they are of little or no direct danger to human life. Still, they can result in serious economic damage (e.g. soil erosion). A lot of data collection centres are working to fill this gap. The present work will not deal with this work, but it will focus on the professional bases and background of the processes causing danger. According to the United Nations International Strategy for Disaster Reduction (UNISDR) office, a disaster often results from natural hazards as a kind of “continuation” of these hazards. But not all dangers lead here. It depends a lot on the circumstances. A disaster causes serious human, physical, economic or environmental damage that disrupts the functioning of society and results in a failure to use society’s resources. The severity of the disaster depends on the impact of the environmental hazard on society and the environment. However, the magnitude of the impact depends on what decisions we make that provide a more stable, predictable state for our lives and our environment (e.g. what type of development we want to pursue in the light of, for example, the IPCC scenarios). Every decision and action can make us more vulnerable or resilient to disasters (Singh & Zommers, 2014). Vulnerability is a complex category of natural, social and economic factors. Environmental load (or the exposure of the given region to it), the susceptibility of the affected region and its ability to adapt to the effects play significant roles in the system described in Sect. 1.5 in more detail. Together with natural and social factors, this relationship between load and adaptability reflects vulnerability, in other words, the buffer capacity of the area, sometimes given as capacity (NATéR, 2016). According to this approach, the relationship between the intensity of the hazard and the degree of vulnerability characterises the magnitude of the natural hazard. Similarly, the term “risk” is also used a lot. There are several definitions of it, but it essentially expresses the extent of (human and physical) loss in a given area over a given period due to a dangerous event (RISK). More specifically, risk consists of the elements of the physical environment (the frequency, magnitude, length, speed, etc., of the risk) and social danger (vulnerability, social factors), and it is not at a large “distance” from the concept of susceptibility. Risk management aims to reduce the degree of threat, which is hindered not only by the complexity of the system but also by the uncertainty of the active processes (e.g. random appearance, the special characteristics of the elements involved). Others interpret risk as a “cross section” of the system of concepts of danger, vulnerability and exposure (Montz et al., 2017). There has long been a need to quantify risk, but many solutions are known due to many factors. The basic context is that risk is the product of the probability of occurrence of a hazard and its severity, which can be expressed as follows: Ri = pi Hi , where Ri is the risk of the ith factor, H i is the risk of the ith factor, and pi is the probability of its occurrence. An environmental/natural disaster is a combination of danger and vulnerability when there is no way to reduce risk potentially. A flood or earthquake hazard in a more vulnerable environment can lead to disaster, which can cause greater damage

1.3 Overall Impacts and Consequences of Natural Hazards in Numbers

11

to human and economic conditions. We have already mentioned that a landslide in an uninhabited mountain region or earthquake in an uninhabited desert does not cause a catastrophe due to a lack of human participation, regardless of the intensity of the natural process. Natural hazards that cannot be copied due to existing vulnerabilities can lead to disasters. They can also have a major impact on the society, environment and economic wealth of the countries concerned. Climate-related sectors such as agriculture, tourism and water are heavily susceptible to this relationship due to the increase in the number and magnitude of extreme events (IPCC, 2012). The volume also seeks to reveal the relationship between natural hazards and anthropogenic climate change and how the changing climate will affect the occurrence of hazards in the future.

1.3 Overall Impacts and Consequences of Natural Hazards in Numbers Natural hazards are natural processes, which often make society suffer and the living environment (or sometimes they mobilise them). It is precisely these effects, up to the level of disaster, that makes it important to discuss this issue. Professionally sound support can help reduce the consequences, which justifies focusing on the study of hazards. With an anthropocentric approach, the direct and indirect types of the impacts of natural hazards can be distinguished. Direct effects include deaths, serious injuries, injuries, health and economic damage in general, while indirect effects primarily involve emotional concerns. Of course, the effects are very diverse because a trigger mechanism is inherently incorporated in the system, i.e. one hazardous element often sparks the emergence of another hazard, e.g. a heavy rainfall may cause a flash flood, which in turn can cause significant soil erosion. This chain of causation is presented separately for each hazard. The effects can also be analysed from other points of view, for example, a financial point of view. Direct effects are more likely to be quantified in terms of individuals and indirect ones in a community. The effects also greatly depend on the social and financial condition of the society, which are discussed in the following sections. It can be stated in general that a population with higher financial income is exposed to less damage in all respects. In the previous century, about 1.3 million people died due to the (direct) effects of natural hazards, 3.1 million people were affected by the events in terms of their health, and the losses amounted to $1644 billion (Guha-Sapir et al., 2013). Disasters are also highly dependent on socio-economic backgrounds, and the same hazard can result in fewer deaths but greater material losses in countries with higher relative income (GDP). Of course, the primary goal with hazards is to reduce their impact, but nowadays, there are also natural hazards that positively impact certain ecological services. The number of such hazards is relatively low. However, we will refer to such hazards, for example, when Egyptian agriculture used flooding for thousands of years to fill river

12

1 General Analysis of Natural Hazards

floodplains with fertile soil, or the effect of forest fires certain pathogens are killed, fertile ash accumulates in the soil, which helps rapid regeneration after a fire in the plant communities or when volcanic material can also serve as a basis for fertile soils, which are also exploited by a lot of vineyards. If we want to assess natural hazards, it is often not the number of their appearance, but their tendency or frequency seems to be the most authentic solution. A more uncertain interpretation can often lead to different results based on very large, extensive databases. We used data from WMO, the Belgian government, the United Nations, and Munich Reinsurance, and we recommend that they should be combined with each other and only in themselves (Table 1.4). From now on, the data in this section are typically derived from here. As we wrote earlier, natural hazards vary in space and time, but their occurrence has some common features. An example is that the intensity and frequency of hazards are inversely proportional to each other. For example, the number of highmagnitude earthquakes is much lower than that of low-magnitude earthquakes, or floods affecting a large area with a large body of water are less frequent than small floods. If we look at the figures of different natural hazards (irrespective of intensity), according to Fig. 1.1, their number increased until the 2000s. Suppose we study the occurrence of disasters on a regional scale. In that case, it is important to note again that these are documented, recorded cases, independently of whether we look at information from either state or insurance companies (Fig. 1.3). About 7500 disastrous events have been recorded over the past 20 years, of which about 5500 were floods and windstorms, 500 earthquakes, 400 extreme temperatures, 350 droughts, 100 volcanic activities, etc. (Wallemacq et al., 2018). When analysing the number of natural hazards, it is not only their number that is difficult to determine (more precisely), but also the trend of their changes. Due to the complex nature of Table 1.4 Large databases on natural hazards and disastersa Database

Service provider

EMDAT

WMO and the Belgian government https://www.emdat.be

EarthObservatory

NASA

https://earthobservatory.nasa.gov/ topic/natural-event

Natural hazards data

US National Oceanic and Atmospheric Administration’s National Geophysical Data Center (NGDC)

https://www.ngdc.noaa.gov/haz ard/hazards.shtml

OurWorldInData

UN’s Sustainable Development Goals (SDGs)

https://ourworldindata.org/naturaldisasters

NatCatSERVICE

Reinsurer in Munich

https://natcatservice.munichre. com/?filter=eyJ5ZWFyRnJvbSI 6MjAxMywieWVhclRvIjoyMDE 4fQ%3D%3D&type=1

a More

Availability

detailed information on all-natural hazards can be found in the chapter dealing with them

1.3 Overall Impacts and Consequences of Natural Hazards in Numbers

13

Fig. 1.3 Number of meteorological disasters on Earth between 1980 and 2011, according to the set of values discussed (after EMDAT, 2019; Montz et al., 2017; Sing & Zommers, 2014)

the processes, it is a question of the extent to which they should be considered natural and social risks. The data (Fig. 1.3; Table 1.5) clearly show that the number of hazards and disasters increases. Still, based on what has been written before, it is partly due to the significantly more advanced, present-day communication (we can receive more detailed information much sooner) and growing population (more and more people are exposed to natural hazards). Several studies focus on investigating the reasons for the high population density in these areas. We already indicated in Sect. 1.1 that the number of these events, and often the events themselves, is not well defined. Therefore, our compilation uses multiple data sources, such as data published by an insurance company or state-controlled data (in the previous case, it is also in the data subjects’ interest to report the event). According to data from an international organisation handling environmental data, the number of reported natural disasters has almost quadrupled since 1970 (EMDAT = International Disaster Database, EMDAT, 2019). It is largely explained by the increase in the number of meteorological and hydrographic hazards (and, to a lesser extent, an increase in the number of windstorms). Looking at a shorter duration and a more detailed breakdown by type, the increase in the number of hazards caused by extreme temperatures and droughts over the past 30 years has been modest (Fig. 1.3). The number of natural hazards is also an important issue for communication. The news networks typically consider news which have visually marketable value. These are events that are faster and easier to interpret, such as volcanic eruptions, earthquakes or severe floods (Ritchie & Roser, 2014). Because of this, hazards/disasters appear as news with a different number of human victims. For example, hunger or malnutrition is included in the news if it has 40,000 casualties, or if it is 3000 victims due to the extreme climate, 2400 due to the drought, but at least is two casualties in the event of an earthquake or volcanic eruption. Moreover, news has high priority when they take place in Europe or North America (Eisensee & Strömberg, 2007).

14

1 General Analysis of Natural Hazards

Table 1.5 Trend of changes in human losses between 1988 and 2019 Year Drought Earthquake Extreme Extreme Flood temperature weather

Mass Volcanic Wildfire movement activity

1988 1600

27,049

644

3335

8504

952

1989 237

650

381

4256

4716

445

1990

42,853

979

4604

2251

98

7 1 33

1991 2000

2454

835

146,297 5852

728

683

90

1992

4033

388

1342

5315

712

1

122

1993

10,088

106

2965

6150

1418

99

3

101

1994

1242

341

4239

6771

307

1995

7739

1730

3763

7956

1521

1996

576

300

4581

8047

1155

4

801

53

84 29 45

1997 732

3159

604

6150

7685

1998 20

9573

3269

24,935

10,653 1141

150

266

1999 361

21,869

771

12,270

34,807 445

70

2000 80

217

941

1354

6025

1012

47

2001 99

21,348

1787

1911

5014

786

33

2002 588

1639

3369

1382

4236

1100

200

6

2003 9

29,617

74,698

1049

3910

706

2004 80

227,290

255

6547

6982

313

2

14

47

2005 149

76,241

1550

5251

5754

664

3

45

2006 134

6692

4826

4329

5843

1638

5

13

2007

780

1086

6035

8607

271

11

148

16

2008 8

87,918

1688

140,985 4007

504

2009

1893

1386

3287

3627

723

2010 20,000

226,733

57,188

1564

8356

3427

323 3

86 190 166

2011

20,946

435

3103

6163

309

2012

711

1834

3105

3544

501

21

2013

1120

1821

8603

9836

235

35 102

10

2014

774

1168

1424

3532

943

2015 35

9550

7425

1270

3495

1006

67

16

2016

1311

490

1760

4720

361

39

2017 0

861

133

1014

3086

2080

0

167

2018 0

4321

536

1666

2869

275

878

247

2019 77

259

2908

2519

5100

719

21

116

Source CRED (2015) and HDIRank (2019)

1.3 Overall Impacts and Consequences of Natural Hazards in Numbers

15

The trend is understandably in line with climate change. Regionally, Asia is the most affected region regarding the highest number of recorded events on this scale. America follows Asia regarding the number of events, mostly meteorologically recorded disasters. At the same time, the number of geophysical and hydrological disasters in Asia and the number of meteorological and hydrological disasters in Europe must be highlighted. The map of Fig. 1.2 summarises the territorial distribution of the registered natural hazards of the last five years.

1.3.1 Human Aspects of Natural Hazards and Disasters The primary measuring parameter of the impact of natural hazards and disasters is human based; it shows how many people died, were injured or were affected by the event. The other measuring parameter is the value caused by the damage and its natural–social consequences. About primary parameters, mortality prompted extensive epidemiological analyses. This index is typically about much better-documented disasters and less about natural hazards affecting a much wider range. While hazards pose a continuous risk, most deaths are caused by relatively few but large catastrophic events—e.g. the tsunami in 2004 or the earthquake in Haiti in 2010, which together caused the death of half a million people (Table 1.5). The number of disaster victims related to droughts and floods has significantly declined globally over the past century in relation (Fig. 1.4). Of course, this significant decrease of about 80% does not mean that the number of hazards and disasters has decreased to such an extent. Still, it is rather the result of significantly better management, conscious preparation, e.g. the establishment of early warning systems in the case of a tsunami (it is already another issue that most of them do not work),

Fig. 1.4 Global deaths from natural hazards between 1900 and 2016 according to EMDAT (2017). Source Ritchie and Roser (2014)

16

1 General Analysis of Natural Hazards

Table 1.6 Changes in human and financial losses by the country group between 1971 and 2010, based on the Human Development Index (HDI) (after CRED, 2015; HDIRank, 2019; HDI) Death (people per HDI index (country group) million people)

Affected population (people per million people)

Cost (per percent of GNI)

1971–1990 1991–2010 1971–1990 1991–2010 1971–1990 1991–2010 Very high

0.9

0.5

196

145

1.0

0.7

High

2.1

1.1

1437

1157

1.3

0.7

Medium

2.7

2.1

11,700

7813

3.3

2.1

Low

6.9

1.9

12,385

4102

7.6

2.8

World

2.1

1.3

3232

1822

1.7

1.0

or the organisation and execution of earthquake preparation (EQP). Overall, the picture is positive, but this favourable trend affected different countries and regions differently. The ourworldindata database compares the number of deaths and injuries related to the disaster and the financial damage caused. The comparison pertained to the average of 2–2 decades between 1971–90 and 1991–2010. The basis of the comparison was the Human Development Index (HDI), consisting of 8–10 economic, social, health and other parameters. Four groups of countries with different values (very high, high, medium, low) can be distinguished. In each of these, the values decreased by 40–300% for these two periods, but the fourfold difference in deaths or costs (these are higher in low-HDI countries) did not change. Most of the victims died in only a few disasters. A good example of their social embeddedness is that 20 of the 100 disasters occurred in Africa, but 60% of the deaths also occurred on this continent (Table 1.6). Between 1994 and 2013, according to the EMDAT database, about 7000 natural hazards claimed 1.3 million lives, which is an average of nearly 70,000 victims a year. However, one must consider that the variance of the data is very large and that data from the same database also contain data indicating lower mortality (CRED, 2015). While ¾ of the deaths were caused by earthquakes (55%) and windstorms (18%), 55% of the more than 4 billion victims were affected by floods and 25% by droughts.

1.3.2 Economic Aspects of Natural Hazards and Disasters In addition to a human-centred analysis of the assessment of events, the financial analysis of the damage is another key factor. Besides the growing population, many hazards have increased within a well-defined framework. At the same time, the number of disasters causing human injuries and deaths has decreased. The same thing cannot be said about many other effects concerning, for example, infrastructure, agriculture, trade or transport. Moreover, the value of the resulting damage shows an

1.3 Overall Impacts and Consequences of Natural Hazards in Numbers

17

exponential increase. The increase in costs caused by natural hazards may mobilise professional investigation to what extent and where there may be reductions in costs. Of course, there are many more common issues, such as how much climate change costs us or how much damage soil erosion causes. We have already started at an earlier stage that a small number of major hazards/disasters have led to the biggest human casualties and sometimes others. Still, only a few events caused most financial damages. According to data of Munich Reinsurance, the ten events with the highest financial loss accounted for 98% of all financial damage (MuRe, 2018, there are other data with a similar conclusion—Balance, 2018; Montz et al., 2017). There are numerous historical examples of such a significant concentration of damage, e.g. the Lisbon earthquake of 1755, as one of the best-known natural disasters known, destroyed nearly half of the region’s GDP. It also launched a series of political changes that led to the end of the Portuguese Empire, followed by 20 years of socio-economic depression. In connection with the management of natural hazards, the primary goal is to reduce and mitigate the risks and effects of hazards. These tasks need to understand these impact relationships accurately and, if we have limited (financial) resources for action, to know the extent of the damage and the future costs associated with rehabilitation. That is, a well-founded cost estimate is also needed to decide. The projected cost of such natural hazards/disasters is important information for, for example, insurers as well. In addition to the (“state”) databases listed in Table 1.4, several insurance companies have the significant human capacity to calculate the cost of natural hazards (e.g. Münich Re, Swiss Re, Berkshire Hathaway, Lloyds’s). This information is in their fundamental interest, as they take out insurance against hazards based on their knowledge of the hazards. According to the calculations, data collection and nomenclature of Munich Reinsurance, in 2018, the damage caused by natural hazards was 160 billion USD, of which 58% was meteorological, 20% climatological, 14% hydrological and 8% geophysical hazards (Münich Re, 2018). Half of these disasters were insured. We could say that this amount is not so substantial because if we look at the dangers and disasters that caused significant financial losses, there are events that only in themselves, together with their direct and indirect effects, caused such damage. Table 1.7 shows the events that caused the most financial damage. On average 20 years, one serious incident per day does not seem to be much (while there are five low-intensity earthquakes per day), but some serious hazards can cause significant damage. The data are presented in Table 1.7 partly coming from the sources shown in Table 1.4, but they are not always verified scientifically, and they are not prepared by employing a homogeneous measurement system (e.g. the incurring costs were calculated with different methods), so they can be considered informative but less reliable. In Table 1.7, the amount of damage calculated at the time of their occurrence was also estimated with the CPI inflation calculator for the current period (for the sake of comparability). Financially, the greatest damage is caused by earthquakes, tropical cyclones and drought. The list also includes Deepwater Horizon and Chernobyl, typically man-made hazards; the damage to the natural environment is more difficult to measure. It is difficult to carry forward the cost of a disaster 30 years ago, so there

87,587

107

3057–8498

148

125

125

≥91.6

68.7

64.8

3

4

5

6

7

8

134

233

1245–1836

5502–6434

197

2

15,894

Fatalities (persons)

360

1

Cost ($billions)

Table 1.7 Fifteen most expensive disasters Type of the catastrophe

Geophysical (earthquake)

Geophysical (earthquake)

Hurricane Irma (https://en.wikipe dia.org/wiki/Hurricane_Katrina)

Hurricane Sandy (https://en.wikipe dia.org/wiki/Hurricane_Katrina)

Hurricane Maria (https://en.wikipe dia.org/wiki/Hurricane_Katrina)

Hurricane Harvey (https://en.wikipe dia.org/wiki/Hurricane_Katrina)

Meteorological tropical cyclone

Meteorological tropical cyclone

Meteorological tropical cyclone

Meteorological tropical cyclone

Hurricane Katrina (https://en.wikipe Meteorological tropical cyclone dia.org/wiki/Hurricane_Katrina)

Sichuan earthquake (https://en.wik ipedia.org/wiki/2008_Sichuan_ear thquake)

Great Hanshin earthquake (https:// en.wikipedia.org/wiki/Great_Han shin_earthquake)

T¯ohoku (Fukushima) earthquake and Geophysical (earthquake, tsunami (https://en.wikipedia.org/ tsunami) wiki/2011_T%C5%8Dhoku_earthq uake_and_tsunami)

Event

2017

2012

2017

2017

2005

2008

1995

2011

Year

North America

North America

North America

USA

USA

China

Japan

Japan

State/continent

(continued)

18 1 General Analysis of Natural Hazards

4800–17,000

104

57

185

31–46

53.25

49.6–56.1

49

45.7

40

50–433

10

11

12

13

14

15

Source COSTdisasters

11

60–100

815

Fatalities (persons)

Cost ($billions)

9

Table 1.7 (continued) Type of the catastrophe

Geophysical (earthquake)

Hydrological (drought)

Hydrological (drought)

Chernobyl disaster (https://en.wik ipedia.org/wiki/Chernobyl_disaster)

Christchurch earthquake

Technological (radiation contamination)

Geophysical (earthquake)

Thailand floods (https://en.wikipe Hydrological (flood) dia.org/wiki/2011_Thailand_floods)

Northridge earthquake (https://en. wikipedia.org/wiki/1994_Northri dge_earthquake)

North American drought (https://en. wikipedia.org/wiki/1988%E2%80% 9389_North_American_drought)

North American drought (https://en. wikipedia.org/wiki/1988%E2%80% 9389_North_American_drought)

Deepwater Horizon oil spill (https:// Technological (oil contamination) en.wikipedia.org/wiki/Deepwater_ Horizon_oil_spill)

Event

1986

2011

2011

1994

2012

1988

2010

Year

The former Soviet Union

New Zealand

Thailand

USA

USA, Canada

USA, Canada

USA

State/continent

1.3 Overall Impacts and Consequences of Natural Hazards in Numbers 19

20

1 General Analysis of Natural Hazards

is considerable uncertainty in the data. Still, it can even be considered as the risk having the largest financial damage in this group. Calculating the financial damage caused by hazards is not an easy task in several ways. Many aspects need to be considered, and many problems need to be solved when answering this very complex question. The difficulties one may encounter include, for example, the fact that lots of parameters cannot be measured or cannot be quantified, the economic impact of the hazard does not end with the event itself, and the immediate loss cannot be given well. Preliminary data can also be very uncertain; see the long-term data on Chernobyl in Table 1.7. At the same time, the human and financial changes of disasters seem to be related. The financial loss caused by the damage occurs with shorter and longer delays in a temporal and spatial sense, depending on the type of the disaster (Fig. 1.5). Calculating the cost of hazard-related damage is also a complex task because, given the system, it must first be clarified which hazards are analysed (e.g. flood, inland excess water, drought, soil erosion, earthquake, etc.) and which economic activities (e.g. industry, transport, housing, agriculture, human health, etc.) are linked to these cases. These also essentially determine the selection of the applicable parameters. Knowing the system (considering the relationship system of the factors) enables several examples for the calculation. In connection with drought, for example, the affected manufacturing companies, households and human health should be included in the system in terms of direct effects, and indirect effects arising from services should also be included (Ding et al., 2010; González et al., 2017). In the case of direct damaging effects, there is a physical link between the natural hazard and the entity affected. This effect can be tangible, e.g. it affects the building or other infrastructure, or it is not tangible (non-market type), difficult to express financially, or difficult to measure, such as damage to health or a decrease in the aesthetic value of the landscape (Fig. 1.6). A variety of methods with varying complexity are known to be used for calculating direct costs, e.g. a hydro-economic model, using only one parameter, which is supported by a cost-input analysis related to water

Fig. 1.5 Financial damage caused by natural disasters (USD 1700 billion), global deaths and affected population between 2000 and 2012, according to UN data. Source UNISDR (2019)

1.3 Overall Impacts and Consequences of Natural Hazards in Numbers

21

Fig. 1.6 Types of damage caused by natural hazards (Meyer et al., 2013)

supply (Grossmann et al., 2011), or a multiparametric model-based risk calculation (Penning-Rowsell et al., 2005). It is considered another type of damage when the natural hazard interrupts the production process. Because on the workplace, industrial production cannot be continued or work on agricultural land is not possible because of inland excess water cover. They are examples of non-tangible damage, e.g. damage to ecosystem services (Fig. 1.6). Indirect costs, which may arise when a natural hazard influences the relationship of a system’s actors (such as suppliers in a production process), form a large group. Intangible or non-market costs may include damage events that are not or only hardly measurable, e.g. cultural heritage involvement, health effects or environmental effects in this sense. Risk mitigation costs include the direct and indirect costs of research, design, infrastructure, operation and maintenance related to hazards.

22

1 General Analysis of Natural Hazards

Following the logic of the previous cost types, it can be stated that in case drought occurs, direct financial effects include the decrease in the yields of arable land products, tourism, different water problems such as business interruption due to critical water utilisation, or irrigation is limited due to lack of water. In contrast, indirect effects include the intangible cost of installing irrigation equipment, and risk mitigation costs may include using drought-tolerant plant species in agriculture. After calculating the numerous cost elements, the question arises, how they will become financial value. This information is particularly important in terms of recording status and the degree of help, mostly because a frequent accusation is that the costs of the impacts are often significantly either underestimated or overestimated. All that is certain concerning the results is that the value of the damage increases very dynamically (Fig. 1.7). The calculation itself is very simple, unlike giving the value of each factor. Using multiple components is a good 50-year-old idea (Mukerjee, 1971). The total loss can be given as follows (Montz et al., 2017): Total loss = L DI + L In + CADI + CAIn − BADI − BAln , where L DI —direct and indirect tangible losses, L In —the cost of intangible damage, CADI —direct and indirect costs resulting from either the interruption of the processes or their adjustments, CAIn —intangible costs, BADI —direct and indirect cost benefits

Fig. 1.7 Financial damage of 35,000 natural disasters from 1900 on, according to the CATDAT database (2016)

1.4 Logical Steps for Reducing the Impacts of Natural Hazards

23

of the adjustments and BAln —their intangible benefits on the cost side. This calculation differs slightly from the earlier presented framework, which groups cost around five factors and considers value-increasing factors.

1.4 Logical Steps for Reducing the Impacts of Natural Hazards Reducing the negative impacts of natural hazards is a fundamental interest and objective of society, which requires a comprehensive understanding of how the system works. In some cases (e.g. earthquakes or extreme temperatures), only a few parameters control the development of phenomena. In contrast, several key parameters control the process in others (e.g. drought or downhill mass movements). Hazards can physically develop because of a combination of these factors. As indicated above, this compilation aims to provide an overview of how the consequences of natural hazards can mitigate. For this purpose, it is only possible to outline where the hazard and its effects can be reduced and where intervention is and can be worthwhile. It should be clear that, in general, systems offer opportunities for action at several points, but that effective intervention is only possible if the factors at play are known and addressed. At the same time, the damage occurs in the other part of the system (between the effects). The logical framework followed in discussing hazards is shown in Fig. 1.8. Many questions may arise about the operation of the system and the factors themselves. However, the basic question is what the purpose of this study is. It is possible to examine how a natural hazard physically develops as an interaction of certain factors; it is possible to analyse its extent, type and characteristics. The effects of the hazards can also be examined from the point of view of the involvement of man

Fig. 1.8 Framework for analysing natural hazards. Source Own construction

24

1 General Analysis of Natural Hazards

and the living environment, or the extent of the resulting damage and the possibilities of recultivation can also be analysed. It is possible to build a monitoring system, which is now a very common goal, and all these, of course, can affect all components of a hazard, from the basic parameters to the effects. Such systems still work today. We only need to think of meteorological, hydrographic, geotectonic and similar measurement networks. Different technical devices can be used to monitor hazards at different speeds, such as floods or excess inland water employing remote sensing, in addition to buoys or earthquakes or tsunami with seismographs or with altimeters (Satellite Altimetry). Developed, sometimes standardised, know-how is also available to measure impacts. These observations can record the results of each step of the process accurately. What is missing is projecting the process forward. Users are more interested in what to expect in the future than what happened to climate, hydrographic and earthquake-related hazards in the past. Of course, forecasting carries a lot of uncertainty, and therefore, only a trend-based answer can be given to these questions.

1.4.1 Early Warning Systems Natural hazards cannot be ruled out in principle, so operating early warning systems (EWS) may be appropriate to reduce human life and property damage. Setting up an EWS system does not seem complicated at first, but operating it is a complex task. On the one hand, it is necessary to determine which process needs to be predicted (e.g. flood, inland excess water, drought) to achieve this task. On the other hand, authentic and well-founded information must be collected for communication. A professional person needs to report on the measured and modelled results. Finally, it is also necessary to have an appropriate amount of time. There is no standard for the preparation and operation of EWS; they depend on the type and temporal scale of the hazards and the territorial features involved. Therefore, many solutions are possible within the EWS system, but the framework of the system can logically be composed of scientific, technical, decision-making and action parts (Zschau & Küppers, 2003). In this system, the monitoring of the elements of the process ranges from the selection of the appropriate sensors, through the collection and processing of data, to the selection of models—hurricane forecast. The results of the predictions calculated by the model(s) are displayed in the form shown in Fig. 1.9. The models are used not only for short-term forecasting, but the method ECMWF (2019) also combines dozens of parameters for analysis, such as air pressure, temperature, wind and so on. Based on the applied high-resolution deterministic climate models, short-term (2–10 days) and long-term forecasts of up to one year can be made. This approach provides a good basis for specifying the spatial extent and temporal variation of the extent of the hazard (e.g. severity of drought, extent of flooding). And based on this, it also provides a basis to make decisions to reduce the consequences and launch-related activities.

1.5 Management of Natural Hazards

25

Fig. 1.9 Application of the EWS as illustrated by Hurricane Katrina, which is also notable for its magnitude of damage. Source National Hurricane Center

1.5 Management of Natural Hazards Reducing the impact of natural hazards must be addressed in well-defined directions or “hot spots”. It also means that a reliable reduction can only and always be implemented only in specific cases, considering the influencing factors. Initially, it is also necessary to decide what kind of hazard management one chooses. This impact reduction, presented in more detail in connection with each hazard in the following chapters, can be approached from two basic perspectives. The action can be either reactive, i.e. the goal is to provide a remedy for the already present and harmful consequences of the effect as soon as possible, or proactive, in which we take preventive measures to prevent natural hazards, more realistically, to minimise damage. An earthquake cannot be avoided, but in this case, a proactive attitude means, for example, the operation of a tsunami warning system (there are several of these from Indonesia to the Caribbean islands) that provide sufficient preparation time to achieve personal safety. Earthquake safety is also an important factor in construction sites, or in the event of large-scale fires, the network of potentially fire-hazardous sites should be easily accessible. As presented in Sect. 1.3, there has been an increase in climatic, consequently hydrological, and consequently other natural (e.g. soil erosion) and social (e.g. increase in the number of relevant diseases) hazards in recent decades. We also mentioned that one hazard might stimulate another, e.g. similar to the “hurricane → high rainfall intensity → erosion chain” of triggers and effects established about most natural hazards. At the same time, the population of the Earth is growing very dynamically, and now the forecasts estimate about 10 billion people by 2050 (compared to the present population of around 7.5 billion, which will fall back to today’s level by 2100). The increase in the population requires significantly larger-scale food production, increasing the supply capacity and more intensive land use. With the development of high population density areas, different geographical surfaces become

26

1 General Analysis of Natural Hazards

vulnerable to natural hazards. Hazards that strike poorly built areas with high population density can cause significant damage. Today, high population density can be considered both the cause and suffering of natural hazards when we think of poor air quality, the frequent scarcity of potable water, increasing pollution or waste treatment. Overall, it can state that natural hazards and population growth provide an incentive to address hazard reduction and management. Management to reduce the impact of natural hazards can be divided into several parts. First, the extent of the hazard, its type, and the users of the results (e.g. governmental organisations, NGOs, media) need to be assessed. An accurate description of the problem can follow this. The procedures that can reduce the risk can be listed: territorial planning, financial support or education. The purpose of the particular procedure (e.g. economic, ecological, social) should be specified. Analyses should specify what model is used to generate them (e.g. hazard or vulnerability) and what parameters and additional analysis methods are used (Newman et al., 2017). In all cases, the aim is to design a system that reduces the impact of hazards. The discussion of related management issues dates back several decades (Haas et al., 1977) and is essentially organised according to the sequence of events of a hazard. Three temporal phases of the management process are distinguished about the time of occurrence of the hazard: preparatory, immediate response and recovery phases. During the professional preparation phase, the causes of the event are identified, and their potential impacts are analysed. There are two key elements to this: firstly, a science-based forecast requires identifying and assessing impact factors and their data sources. Knowledge of the system and the purpose of the study determine what data is (would be) needed. Another element of the technical preparation is recording the management of the proposed action. The logical framework of the process is simple to identify the hazard, mitigate its impact, publish professionally based information and issue the necessary warnings (Fig. 1.10). In chronological order, the prehazard tasks include, in addition to measuring baseline data, measuring vulnerability and sensitivity, mitigation options, hazard prediction and emergency preparedness (Fig. 1.11). Several solutions to these issues are known and applied. Vulnerability, which refers to the weakness of a system and allows hazards to occur, has been defined previously (Sect. 1.2). The evolution of responses—in this case, for example, vulnerability—is well illustrated by an approach that analyses vulnerability as a system characteristic that can be calculated based on sensitivity, adaptive and adaptive capacities, or modelled, for example, by considering changing climatic influences (Fig. 1.11; Pálvölgyi et al., 2010). There are now many organisations providing basic data in all countries. For example, in Hungary, meteorological data are available on met.hu, while hydrographic data are available on vizugy.hu. These do not always provide basic data on natural hazards; for example, snow blowing, or fog cannot be included in the narrow scope of natural hazards, but they also have a statistically based hazard warning system for climate data within their own system (e.g. forecasting extreme temperature or precipitation events).

1.5 Management of Natural Hazards Fig. 1.10 Tasks related to the management of natural hazards (based on Haas et al., 1977)

Fig. 1.11 CIVAS model of climate change susceptibility, based on Pálvölgyi et al. (2010)

27

28

1 General Analysis of Natural Hazards

In the preparatory phase, the key issue is hazard prediction beyond monitoring, data collection, technical status analysis (e.g. vulnerability, resilience) and preparation for potential mitigation of expected impacts. Two concepts are used in this context: “prediction” is more the concept of estimation, and “forecast” can be described by the concept of forecasting (known from meteorology). The first one does not have exactly quantifiable data and/or information, e.g. the extent of inland excess water belongs to estimation, whatever modern equipment is used to monitor it. In such cases, the estimate rather shows the sensitivity on terrains that can be designated as susceptible to inland excess water hazard on a professional basis (e.g. on the edge of an alluvial fan or in a depression on the surface, which prevents the precipitation from filtering into the soil if the depression is covered by clayey sediment). The most common sensitivity estimate is based on simple statistics such as how frequently the area is affected by inland excess water cover. It is the basis for estimation accordingly for the future. A forecast already provides a prediction of the location and extent of the hazard based on the available data, e.g. based on models. Both approaches can be applied if the situation allows it and enough information (Keller & DeVecchio, 2016). The same situation can be estimated from a vegetationfree slope side if the question addresses which particular slope section may have less or more erosion. The Wishmeier–Smith model can be used to predict how much soil is expected to move on the slope with erosion. And we have not talked about the already usual forecast of river water levels, air temperature, expected precipitation (e.g. metoffice.gov.uk) yet, which is discussed in more detail for each natural hazard. The key issue in this block is the forecasting of the threat, more specifically, the professional substantiation of the forecasts and the communication of the results to decision-makers. Such warning systems are known and used for most hazards (e.g. flooding, inland water, extra precipitation, temperature) (see, e.g. Sects. 4.3 and 4.4). In most cases, it is the responsibility and competence of the municipalities (managers) to take measures (warnings, traffic restrictions) and to initiate an alert, if necessary, but this is only the first step. The promulgation of warnings and alerts by both the emergency services and the municipalities is well regulated: it is well defined when and what type of action should be taken measures triggered. The key is to ensure that this process leads to a professionally sound conclusion for decision-makers and that the source data and its professional conclusions are made public. However, this is often handled differently from country to country. When exposed to a hazard, the primary task is to rescue and assist those affected and mobilise local resources to support the rescue. An important issue is collecting and creating the appropriate quantity and quality of information. Experts are responsible for transmitting information and decisions to those concerned, which, e.g. the media, can play an important role. Potential partners, such as NGOs, social policy organisations, scientific and technical institutes, state and civil protection units, should be involved in this process. The result here must (or should) be that the information is communicated in a professionally accurate but comprehensible form. A separate question is how to communicate risks and threats effectively (Golacre, 2011 in Montz et al., 2017). That is, a 100-year flood return probability does not mean that if there was such a flood this year, the next one would only occur 100 years from

1.5 Management of Natural Hazards

29

now. Providing appropriate information is also a priority for those affected by the hazard and those managing the process. Another important question is when, based on a professionally substantiated forecast, which units will initiate and take the decision to mitigate the impact of a natural hazard, and who will lead this process. While it is true that the scale of most natural hazards is not precisely defined—i.e. it is difficult to make a quantitative decision on whether to initiate protection—there are cases, such as floods, where protection is linked to flood protection levels so that protection activities can be initiated at the appropriate level based on quantitative data. The tasks are laid down in legislation. In the case of inland flooding, there is a distinction between inland and outdoor flood risk, where the water management organisation and the municipalities must act based on specific criteria. Information exchange becomes very important if we comprehensively address all direct and indirect impacts beyond the sectoral approach. At present, it is a common practice to analyse and act on each threat and its components separately. This exchange of information is particularly important if we consider that management also depends on scale so that a different technique is needed for action at local or regional scale. Even if not typically from a geoscientific profile, but handling the emergency created by the effects of a hazard or disaster, which takes an average of two weeks, and additional months are necessary to restore the state of the environment, while reconstruction and renovation may take years (Haas et al., 1977; Olshansky et al., 2012). Post-hazard and post-disaster tasks can be included in the scope of rehabilitation and reconstruction. Although these tasks are not comprehensively regulated, it has a process developed several decades ago: the emergency situation lasts 1– 2 weeks, recovery takes 8–10 weeks, reconstruction of the prehazard situation takes 20–100 weeks, and development projects can take another 100 weeks (Haas et al., 1977; Montz et al., 2017). Neither the government nor the EU has a legal obligation to address the consequences of natural hazards, but state aid for mitigation is regular. In addition, individuals must be prepared to deal with hazards. The risk associated with hazards must not only be the responsibility of the state or the community but also of the individual, although the risks and the extent of damage may exceed the significant risk reduction or remediation options of the people living in affected areas. An element of public interest regarding regional planning is the inclusion of (natural) hazards in plans. Building permits will be issued accordingly in countries with this kind of regulation. A lot of methods are known for this. For example, in the USA, in connection with the regional approach, different risks have been identified in certain areas (e.g. what percentage and which part(s) of a site are flood-prone; Montz et al., 2017). In Austria, national hazard zones have been defined for regional planning since 1975. In the case of hydrographic involvement, critical tasks for protection, which are separated in time, should be prioritised and implemented. The action rarely covers all the sectors affected. Water conservancy authorities treat the problems considered to be mainly water-related, the relevant agricultural bodies treat soil-related problems as a homogeneous problem, and the necessary steps are taken. Still, it can be useful,

30

1 General Analysis of Natural Hazards

for example, to take into account the steps of a disaster recovery plan formulated in the IT field (IBM, 2016). It is tempting to analyse all the hazards and risks in a given area together and comprehensively. However, it is mostly not possible due to the complexity of the problem, the ambiguous interpretation of the hazards and the factors’ uncertainty. All this requires an integrated approach, both the intention and the method. However, hazard management has not fundamentally changed for decades, as identifying hazards, finding answers, the strategy of solutions and the implementation process do not differ significantly. However, the newer systems form a more comprehensive system of these events (Fig. 1.8). As a first step in the field of operation, the task is to identify the problem, determine the type of hazard and collect individual and organisational users (controllers, managers) and basic data. Almost all hazard analyses reach this stage. The event then needs to be analysed regarding how we reduce the risk. Only half of the hazard management processes reach this stage. These projects pay little attention to the likelihood of the hazard returning or even less to assessing the level of acceptability of the risk involved (adaptability). In the next step, the applicable model must be selected by the problem, e.g. vulnerability, sensitivity, but the selected method can also be a static or a dynamic, process- or experience-based method (e.g. MATRIX—Newman et al., 2017; Wenzel, 2012).

Bibliography Alexander, D. E. (1993). Natural disasters (p. 632). Springer Science & Business Media. Blong, R. (2003). A review of damage intensity scales. Natural Hazards, 29(1), 57–76. Brázdil, R., Kiss, A., Luterbacher, J., Nash, D., & Reznickova, L. (2018). Documentary data and the study of past droughts: A global state of the art. Climate of the Past, 14, 1915–1960. Bryant, E. (2005). Natural hazard (p. 330). Cambridge University Press. Cutter, S. L., Boruff, B. J., & Shirley, W. L. (2003). Social vulnerability to environmental hazards. Social Science Quarterly, 84(2). Ding, Y., Hayes, M., & Melissa, W. (2010). Measuring economic impacts of drought: A review and discussion (Papers in natural resources, 196). University of Nebraska, Lincoln. http://digitalco mmons.unl.edu/natrespapers/196 Douglas, I., Huggett, J. R., & Robinson, M. E. (1996). Companion encyclopedia of geography: The environment and humankind (p. 1021). Routledge. Eisensee, T., & Strömberg, D. (2007). News droughts, news floods, and U. S. disaster relief. The Quarterly Journal of Economics, 122(2), 693–728. https://doi.org/10.1162/qjec.122.2.693 Flanagan, B. E., Gregory, E. W., Hallisey, E. J., Heitgerd, J. L., & Lewis, B. (2011). A social vulnerability index for disaster management. Journal of Homeland Security and Emergency Management, 8(1), 3. http://www.bepress.com/jhsem/vol8/iss1/3 Gebhardt, H., Glaser, R., Radtke, U., Reuber, P., & Vött A. (Eds.). (2017). Geographie. Springer Spektrum. Godschalk, D. R. (2003). Urban hazard mitigation: Creating resilient cities. Natural Hazards Review, 4(3), 173–179. González, J., Decker, C., & Halla, J. W. (2017). The economic impacts of droughts: A framework for analysis. Ecological Economics, 132, 196–204. Grossmann, M., Koch, H., Lienhoop, N., Vögele, S., Mutafoglu, K., Möhring, J., Dietrich, O., & Kaltofen, M. (2011). Economic risks associated with low flows in the Elbe River Basin (Germany):

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An integrated economic-hydrologic approach to assess vulnerability to climate change (GLOWAElbe working paper). https://www.pik-potsdam.de/glowa/pdf/schlussbericht_glowaii/Arbeitspa piere/grossmann.pdf Guha-Sapir, D., Hoyos, P., & Below, R. (2013). Annual disaster statistical review 2013: The numbers and trends. CRED. http://www.cred.be/sites/default/files/ADSR_2013.pdf Haas, J. E., Kates, R. W., & Bowden, M. J. (Eds.). (1977). Reconstruction following disaster (p. 331). MIT Press. https://www.oas.org/dsd/publications/Unit/oea66e/ch01.htm#c.%20hazard%20mana gement%20and%20development%20planning ISDR. (2004). Living with risk: A global review of disaster reduction initiatives. International strategy for disaster reduction. United Nations Publications. ISBN: 9211010640. Keller, E., & DeVecchio, D. (2016). Natural hazards (p. 554). Routledge. Kiss, A. (2005). Utilisation of the inundation area at Lake Ferto before regulation works: Example of Sarród and its surroundings. Acta Geographica, 38, 39–49. Meyer, V., Becker, N., Markantonis, V., Schwarze, R., van den Bergh, J. C., Bouwer, L. M., Bubeck, P., Ciavola, P., Genovese, E., Green, C., & Hallegatte, S. (2013). Review article: Assessing the costs of natural hazards—State of the art and knowledge gaps. Natural Hazards and Earth Systems Sciences, 13, 1351–1373. Montz, B. E., Tobin, G. A., & Hagelman, R. R. (2017). Natural hazards: Explanation and integration (p. 455). The Guilford Press. Mukerjee, T. (1971). Economic analysis of natural hazards: A preliminary study of adjustments to earthquakes and their costs (Natural hazards research working paper 17). Institute of Behavioral Science, University of Colorado, Boulder. Newman, J. P., Maier, H. R., Riddell, G. A., Zecchin, A. C., Daniell, J. E., Schaefer, A. M., van Delden, H., Khazai, B., O’Flaherty, M. J., & Newland, C. P. (2017). Review of literature on decision support systems for natural hazard risk reduction: Current status and future research directions. Environmental Modelling & Software, 96, 378–409. Olshansky, R. B., Hopkins, L. D., & Johnson, L. A. (2012). Disaster and recovery: Processes compressed in time. Natural Hazards Review, 13(3), 173–178. Pálvölgyi, T., Czira, T., Dobozi, E., Rideg, A., & Schneller, K. (2010). A kistérségi szint˝u éghajlatváltozási sérülékenység vizsgálat módszere és eredményei. klíma 21 füzetek, 62, 88–102. Peduzzi, P., & Herold, H. D. C. (2005). Mapping disastrous natural hazards using global datasets. Natural Hazards, 35(2), 265–289. Penning-Rowsell, E., Floyd, F., Ramsbottom, D., & Surendran, S. (2005). Estimating injury and loss of life in floods: A deterministic framework. Natural Hazards, 36, 43–64. Sheffield, J., Andreadis, K. M., Wood, E. F., & Lettenmaier, D. P. (2009). Global and continental drought in the second half of the twentieth century: Severity–area–duration analysis and temporal variability of large-scale events. Journal of Climate, 22(8), 1962–1981. Singh, A., & Zommers, Z. (Eds.). (2014). Reducing disaster: Early warning systems for climate change (p. 387). Springer. Toonen, W. H. J. (2015). Flood frequency analysis and discussion of non-stationarity of the Lower Rhine flooding regime (AD 1350–2011): Using discharge data, water level measurements, and historical records. Journal of Hydrology, 528, 490–502. Wallemacq, P., UNISDR, & CRED. (2018). Economic losses, poverty and disasters 1998– 2017. https://doi.org/10.13140/RG.2.2.35610.08643. https://www.researchgate.net/publication/ 331642958_Economic_Losses_Poverty_and_Disasters_1998-2017 Wenzel, F. (2012). Decision-analytic frameworks for multi-hazard mitigation and adaptation, new methodologies for multi-hazard and multi-risk assessment methods for Europe. Karlsruhe Institute of Technology. Wilhite, D. A., Svoboda, M. D., & Hayes, M. J. (2007). Understanding the complex impacts of drought: A key to enhancing drought mitigation and preparedness. Journal of Water Resource Management, 21(5), 763–774.

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Zlateva, P., Pashova, L., Stoyanov, K., & Velev, D. (2011). Social risk assessment from natural hazards using fuzzy logic member. IACSIT International Journal of Social Science and Humanity, 1(3). Zschau, J., & Küppers, A. N. (Eds.). (2003). Early warning systems for natural disaster reduction (p. 834). Springer.

Internet-Based Sources (Download 15.10.2020) Balance. (2018). https://www.thebalance.com/cost-of-natural-disasters-3306214 Bangladesh. (1991). https://www.history.com/topics/natural-disasters-and-environment/bangla desh-cyclone-of-1991 CATDAT. (2016). https://phys.org/news/2016-04-natural-disasters-1900over-million-deaths.html COSTdisasters. https://en.wikipedia.org/wiki/List_of_disasters_by_cost CRED. (2015). https://www.preventionweb.net/files/42895_cerdthehumancostofdisastersglobalpe. pdf ECMWF. (2019). https://climate.copernicus.eu/ EDO. (2014). European drought observatory. Joint Research Centre, ISPRA. Retrieved January 8, 2015, from http://edo.jrc.ec.europa.eu/edov2/php/index.php?id=1000 EMDAT. (2017). https://emdat.be/sites/default/files/adsr_2016.pdf EMDAT. (2019). http://www.emdat.be/ EQP. Földrengés el˝okészület. www.acphd.org/.../disaster_and_earthquake_preparedness_daycare. p... HDI. https://ourworldindata.org/natural-disasters#link-between-poverty-and-deaths-due-to-enviro nmental-causes HDIRank. (2019). http://hdr.undp.org/en/data Hurricane. (2019). http://www.weather.com/weather/hurricanecentral/tracker, http://www.nhc.noa a.gov Hurricane forecast. http://derecho.math.uwm.edu/models/models.html IBM. (2016). https://www.ibm.com/support/knowledgecenter/hu/ssw_ibm_i_73/rzarm/rzarmdisa str.htm IPCC. (2012). https://www.ipcc.ch/site/assets/uploads/2018/03/SREX_Full_Report-1.pdf IPCC. (2014). https://www.ipcc.ch/site/assets/uploads/2018/02/AR5_SYR_FINAL_SPM.pdf IPCC. (2018). https://www.ipcc.ch/site/assets/uploads/sites/2/2019/06/SR15_Full_Report_ High_Res.pdf MURe. (2014). https://reliefweb.int/sites/reliefweb.int/files/resources/Munich-Re-World-map-Nat ural-catastrophes-2014.pdf MURe. (2018). https://www.munichre.com/topics-online/en/climate-change-and-natural-disasters/ natural-disasters/the-natural-disasters-of-2018-in-figures.html#&gid=1&pid=1 MURe. (2019). https://natcatservice.munichre.com/?filter=eyJ5ZWFyRnJvbSI6MjAxMywieWV hclRvIjoyMDE4fQ%3D%3D&type=1 Münich Re. (2018). https://www.munichre.com/topics-online/en/climate-change-and-natural-dis asters/natural-disasters/the-natural-disasters-of-2018-in-figures.html#&gid=1&pid=1 NASA. (2005). https://earthobservatory.nasa.gov/world-of-change/DecadalTemp/show-all NATéR. (2016). Sérüléskenységelemzés.pdf. https://nater.mbfsz.gov.hu/sites/nater.mfgi.hu/files/ files/Osszegzo_HU.pdf National Hurricane Center. http://derecho.math.uwm.edu/models/models.html RISK. https://www.researchgate.net/post/There_is_a_definition_of_risk_by_a_formula_risk_pro bability_x_loss_What_does_it_mean Ritchie, H., & Roser, M. (2014). Natural Disasters. https://ourworldindata.org/natural-disasters Sendai. (2015). https://www.unisdr.org/files/43291_sendaiframeworkfordrren.pdf

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UNISDR. (2009a). UNISDR terminology on disaster risk reduction. https://www.undrr.org/public ation/2009-unisdr-terminology-disaster-risk-reduction UNISDR. (2009b). Global assessment report on disaster risk reduction 2009. Risk and poverty in a changing climate. www.preventionweb.net/gar09 UNISDR. (2019). https://reliefweb.int/map/world/world-disaster-impacts-2000-2012 WRR, Kirch, L., Luther, S., et al. (2017). WorldRiskReport. Analysis and prospects (p. 74). United Nations University. https://reliefweb.int/sites/reliefweb.int/files/resources/WRR_2017_E2.pdf, https://collections.unu.edu/eserv/UNU:5763/WorldRiskReport2016_small_meta.pdf

Chapter 2

Geophysical Hazards

Abstract The chapter deals with the development of four natural hazards: volcanism, earthquakes, the most associated tsunami and slope mass movements and their damage and mitigation options. For each of these hazards is a sketch of how they occur, an explanation of their geographical location, a calculation of the intensity of their activity and an assessment of the magnitude of the human and financial damage caused. The analysis of the consequences also covers the social impact consequences. For each of the natural hazards analysed, the professional (e.g. forecasting, monitoring), technical and human (e.g. communication) tasks of mitigation are discussed in detail.

2.1 Natural Hazards Posed by Volcanic Activity and Mitigation Options Volcanoes are powered by magma. Magma is produced by partial melting in the Earth’s mantle. For more than a century, the theory was accepted that deep igneous rocks were formed by the solidification of the long-lived magma chamber material at shallow depths and that molten rock stored in the magma chamber could reach the surface through the vent. However, geophysical, geochemical, petrological, volcanological and geological observations of the last few decades often contradict the classical magma chamber theory (Cashman et al., 2017). Modern physical models of magmatic processes that combine thermodynamic and mechanical laws have revealed that the structure and formation of magma chambers are much more complex than previously thought. The currently accepted view is that magmatic processes can be traced across the entire thickness of the crust/lithosphere, with the resulting melts accumulating in the shallow regions of the crust/lithosphere to form a magma chamber that represents the uppermost—nearest to the surface—part of a large magmatic system. Open-system processes such as crustal assimilation or recurrent magma intrusion can occur in magma reservoirs. In addition, fractionation and separation of the molten material already start in the lower lithosphere. Depending on its viscosity and the proportion of rock materials, the exposed rock material (lava and pyroclastic material) may form volcanic cones or flowing lava flows. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 G. Mez˝osi, Natural Hazards and the Mitigation of their Impact, https://doi.org/10.1007/978-3-031-07226-0_2

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The occurrence of volcanoes is mainly related to the movement of lithospheric plates, ten times thicker than the Earth’s crust, which moves in the upper part of the viscous mantle (asthenosphere). The primary (basaltic) melts are formed in the asthenosphere due to a decrease in pressure, increased temperature and enrichment of volatiles (mainly H2 O and CO2 ). These melts are responsible, directly or indirectly, for surface volcanic activity.

2.1.1 The Formation and Spatial Distribution of Volcanoes The different composition of the rock plates means that they sink into the asthenosphere to different degrees. The denser oceanic plates are generally situated below sea level, and, as they converge, they dive beneath the continental oceanic plates (subduction zone). The oceanic crust is transformed upon interacting with seawater. As the plates dive beneath at increasing temperatures and pressures, minerals containing OH are transformed, and aqueous solutions are removed from the plate. The mantle layer, which is several kilometres thick above the subducting plate, is dragged downwards. In this layer, the solutions that flow out of the plate accumulate, but they can only escape from there at a depth of around 100 km. The upward flow of aqueous solutions reduces the melting point of the peridotite (mantle rock). A low-density and water-rich melt is formed first, which rises rapidly along with the pores of the rocks. At higher temperatures, the aqueous melt interacts with the peridotite rock of the mantle and melts more and more. The resulting basaltic magma becomes trapped beneath the thick crust. The thermal action of the basaltic magma triggers melting in the lower part of the earth’s crust, from which intermittent magma packages rise into the shallow part of the earth’s crust, forming extensive magma reservoirs. The melts arise from the magma chamber, which contains magma of high silica content and occasionally melts from the deep basaltic melt body, resulting in volcanic eruptions (Fig. 2.1). Spatially, these can be observed along the boundaries of the subducting plates. For example, 62 volcanoes have formed (Fig. 2.2) where the Nazca plate dives beneath the South American plate. The tectonic plates move away from each other in a divergent motion, and volcanoes can form in the process (seafloor) spreading zone. The reduction in pressure (the upward flow of mantle rock material) results in basaltic melts, creating mid-ocean ridges. An example of a volcano forming along faults when plates diverge from each other is the Icelandic Eyjafjallajökull, which is associated with the separation of the Eurasian and North American plates (Fig. 2.3). The third type of volcano formation is associated with hot spots. These are points in the lithosphere below which the mantle temperature rises, the mantle material partially melts, and magma can reach the surface, typically in the form of a basaltic volcano. These points occur both in the interior of oceanic (50 hot spots) and continental (40 hot spots) plates and along rift valleys (about 15 hot spots) (e.g. volcanoes in the Azores, Easter Island, Galápagos, Canary Islands, Hawaii, Iceland and Yellowstone).

2.1 Natural Hazards Posed by Volcanic Activity and Mitigation Options

37

Fig. 2.1 Volcanoes associated with the collision of tectonic plates form when one plate slides underneath the other. Source BGS—British Geological Survey

Fig. 2.2 Location of convergent and divergent plates. Source Volcano Discovery

Volcanoes’ polygenetic or monogenetic nature indicates volcanic eruptions’ frequency (number). Polygenetic volcanoes have usually been active for hundreds of thousands of years, erupting repeatedly and always from similar magma chambers and volcanic conduits. Monogenetic volcanism means a single eruption (e.g. the shield volcanoes of Hawaii or the maar of the Eifel mountains—Photo 2.1). These usually form volcanic fields where numerous volcanoes of relatively small volume have formed due to a single eruption (Molist, 2017).

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Fig. 2.3 Volcanoes associated with divergent tectonic plates (own compilation)

Photo 2.1 Lake Schalkenmehrener is located at the centre of a series of monogenetic volcanic maars in the Eifel mountains in Germany (photo by Eifelinfo, 2019)

Volcanoes can be further grouped according to other criteria (Sigurdsson et al., 2015). Based on the type of eruption, we can talk about explosive (phreatic) and effusive volcanoes, while according to the shape of the eruption site, areal, labial— fissure volcano, centrolabial and central volcanoes are distinguished, but volcanoes can also be classified according to the morphology of their cone (Fig. 2.4).

2.1 Natural Hazards Posed by Volcanic Activity and Mitigation Options

39

Fig. 2.4 Classification of volcano types by shape. a Intact stratovolcano, composed of layers of pyroclastic material and lava; b caldera, a form formed by explosion; c somma, a new volcanic dome within a caldera; d shield volcano, composed mainly of lava (after Brown et al., 2015 own compilation)

2.1.2 The Intensity of Volcanic Activity The potential danger of volcanoes is characterised by the magnitude and intensity of their eruptions but measuring this is not easy. Usually, the total mass mobilised (m3 or kg) is calculated for eruption magnitude, while the eruption velocity or mass/speed ratio is calculated for eruption intensity. This logic is used to calculate the Volcanic Explosivity Index (VEI), based on a long-accepted scheme (Newhall & Self, 1982). The calculated VEI value is recorded on a nine-point scale based on the wellmeasured height of the ash emitted and the volume of volcanic material mobilised (Table 2.1). Historical explosive eruptions, but no other descriptive information is available, have a default VEI value of 2. Fatalities are generally associated with a VEI greater than 6. A “major volcanic eruption” is categorised as one that meets at least one of the following criteria: it is fatal, it causes moderate damage (approximately $1 million or more), it has a VEI of 6 or greater, and it is accompanied by a tsunami or major earthquake. According to the Smithsonian Institution’s volcanic eruption data, about half of all volcanic eruptions are classified as VEI2, while 15–15% are classified as VEI1 and VEI3, according to the Smithsonian Institution’s volcanic eruption data (Loughlin et al., 2015; Siebert et al., 2010). Today, there are a lot of volcanoes on Earth that are active, but their activity is not significant. For example, in 2017, volcanoes in Italy and East Asia (Indonesia) were active with two and four eruptions, respectively (Fig. 2.5). Estimates of the magnitude of volcanic eruptions date back to 1750 BC, but the data’s reliability and completeness deteriorate strongly backwards in time. The detailed database of the Smithsonian Institution contains 866 eruptions dating back to the Holocene (ca. 10,000 years) and 596 since 1500. The database is considered complete from about 1950 to the present when we have more precise data on 347 volcanic eruptions. The logical conclusion from the database is that as the intensity of eruptions increases, their frequency decreases. For this reason, for example, Pinatubo in the Philippines, which had been dormant for almost five hundred years, erupted with VEI6 in 1991, similarly, to Mount St. Helens in 1980 with VEI5, while the volcano had been dormant for a millennium before that. The list of volcanoes in the database is available (Smithsonian, 2014).

Extra scale

Extra scale

7

8

>25

>25

>25

Extra scale

6

10–25

>25

Disastrous

Disastrous

3–15

4

Explosive

3

0.1–1

1–5

5

Weak

Explosive

1

1 × 1012

Ultra-Plinian (supervolcanic)

Ultra-Plinian

1 × 1011 1×

Plinian

1 × 1010

Sub-Plinian

1 × 108 1×

Vulcanian-Peléan

1 × 107 109

Hawaiian-Strombolian Strombolian-Vulcanian

106

1×

Eruption type

Eruptive volume (m3 )

Table 2.1 Volcanic explosion index (after Loughlin et al., 2015; Smithsonian, 2014)

10,000 years

1000 years

100 years

100 years

10 years

Yearly

Weekly

Frequent

Frequent

Frequency

Yellowstone (2 million years ago)

Tambora (1815)

Krakatau (1883)

St. Helens (1981)

Galunggung (1982)

Ruiz (1985)

Galeras (1992)

Stromboli

Kilauea

Example

40 2 Geophysical Hazards

2.1 Natural Hazards Posed by Volcanic Activity and Mitigation Options

41

Fig. 2.5 Number of volcanic eruptions by country in 2017. The website displays data from 1693 to 2017 and contains information on around five hundred significant eruptions. Source eruption and Smithsonian (2014)

2.1.3 Consequences of Volcanic Activity and Related Hazards The impacts of volcanic activity are sometimes underestimated because they affect a small area and cause relatively few casualties. There are undoubtedly positive aspects to volcanic eruptions, such as the potential for the formation of valuable soils on the volcanic pyroclastic flows and the cultivation of a wide range of crops from coffee to grapes on the excellent land. From Iceland to the Hawaiian Islands, numerous examples of geothermal energy are harnessed in connection with volcanic activity, while inactive volcanoes often host telecommunications transmitters. Volcanic rocks are also often quarried, a good example of which is the now protected basalt volcano of Badacsony near Lake Balaton (Photo 2.2). Some volcanic types may contain valuable mineral resources (e.g. gold, silver, platinum, copper). Tourism is also a major attraction. For example, in 2018, Etna was visited by more than 1.5 million tourists and the surrounding area by 3 million. However, we should not forget the almost 300,000 victims of the eruptions and the tens of billions of dollars in direct financial damage. Among the hazards caused by volcanoes, all processes that result in damage to the human or physical sphere caused by the volcanic activity should be considered. These impacts may cause death, injuries or other health effects, property damage, social and economic disruptions or environmental degradation. Natural hazards associated with volcanoes occur before, during and after volcanic eruptions. The hazards are described in several compilations, such as those of the British and American geological organisations (BGS, USGS), the German Helmholtz Centre and several websites

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Photo 2.2 Now inactive basalt volcanoes of the Tapolca Basin, with Badacsony in the middle, were active 3–4 million years ago in the northern part of Lake Balaton (photo by Pál Molnár, E.)

(see Smithsonian, volcanic hazards) and the author (e.g. Keller & DeVecchio, 2016; Loughlin et al., 2015). A pyroclastic flow is a fast-moving, hot and dense mixture of volcanic ash, rock debris, vapours and gases (volcanic hazards; Loughlin et al., 2015). The speed of movement depends on the composition of the mixture, which can range from a cloud of gas or vapour to a dense liquid. Pyroclastic flows claim the most human casualties and cause the most significant economic damage. One of the most wellknown pyroclastic flows caused by the eruption of Mount Vesuvius destroyed the cities of Pompeii and Herculaneum in 79 AD, burying the settlements under thick ash; most of the victims died of asphyxiation (Fig. 2.6). The impact of pyroclastics flows can spread over several kilometres from the eruption site. They account for most of all known volcanic deaths, one-third of all (Auker et al., 2013; GVM). Generally speaking, pyroclastic flows move dangerously fast, so their shock and blast effects often cause injuries or death, while their high temperature makes it difficult to avoid thermal injury (e.g. laryngeal and pulmonary oedema) and asphyxiation (Brown et al., 2017; Photo 2.3). Lahar is composed of volcanic debris and water slurry to form a debris flow. These flows can persist for long periods when thick and loose deposits are present (Photo 2.4). Lahars are primarily formed as a result of heavy rainfall on loose volcanic debris, somewhat similar to a flash flood, but can also occur when the eruption hits a lake or snowy/icy surface. The debris flow, moving at high velocity down the slope, can directly affect settlements tens of kilometres away from the volcano, as well as infrastructure and transport routes. However, waterlogged lahars account for 15% of all historic volcanic deaths (Auker et al., 2013). The largest lahar was formed on the Nevado del Ruiz volcano (Colombia) in 1985, causing tens of thousands of deaths. The explosions accompanying volcanic eruptions produce, in addition to large quantities of debris (also known as tephra, along with pyroclastic), a large amount of material with a grain size of less than 2 mm, known as volcanic ash. The previously deposited volcanic material explosion blows this dust material into the air. The wind carries it, while the volcanic cloud cools and the dust slowly settles. It can

2.1 Natural Hazards Posed by Volcanic Activity and Mitigation Options

43

Fig. 2.6 Some of the processes associated with volcanic eruptions that can cause hazards (USGSvolcano; Harangi, 2011)

Photo 2.3 Pyroclastic flow at the eruption of Sinabung volcano (Sumatra, Indonesia, 2014, photo by Marc Szlegat—volcano flow)

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Photo 2.4 Lahar viewpoint at Mt. St. Helens, WA, USA. Source https://search.creativecommons. org/

cause serious damage to health, the environment, power supplies, communications equipment and transport (Horwell & Baxter, 2006). For example, the eruption of Iceland’s Eyjafjallajökull volcano in 2010 caused volcanic dust to be released into the air, which grounded air travel in Northern Europe for days. (This is, of course, an indirect hazard, similarly to an earthquake caused by a volcanic eruption or a tsunami caused by the water displacement of pyroclastic flows; Molist, 2017.) The deposition of fine ash causes very slow permeability, rapid runoff, increased erosivity and sometimes flash floods. The release of ash into the air also reduces insolation, which can lead to a temporary change in the climate. It was happened in 1815 with the eruption of Tambora (Indonesia). The ash cloud filtered out sunlight, causing crop failures and starvation across the northern hemisphere, and the loss of forage for horses led to the invention of the bicycle. This year was dubbed the “year without summer” or the “year of famine”. Dust released into the air by volcanoes also causes health hazards, with a mortality rate comparable to lahars (Brown et al., 2017). The most immediate effect of a volcanic eruption is lava flow, destroying everything from infrastructure to vegetation. The usually slow-moving lava flows rarely pose a threat to human life, as there is sufficient time to escape, and it is now possible to control the path of lava flows. The release of gases associated with volcanic activity (e.g. sulphur dioxide) poses a serious threat, especially to health and vegetation. This impact is estimated based on the concentration of gases in the atmosphere and the duration of exposure. The emissions, together with precipitation, can lead to acid rain damaging vegetation and soils; the main component of this acid rain is sulphur dioxide, which can form sulphate aerosols in the atmosphere (Lockwood & Hazlett, 2010; Loughlin et al.,

2.1 Natural Hazards Posed by Volcanic Activity and Mitigation Options

45

2015). The Global Volcano Model (GVM) database is the first regional compilation of volcanic hazards focusing on groups of countries and presents the impact of eruptions on society. The documented mortality as a result of volcanic processes is low compared to other natural hazards (around 280,000 deaths since 1600; Auker et al., 2013), but a small number of eruptions cause the majority of these deaths. Nearly two-thirds of deaths in historical times were caused by five disasters, not all of which were eruptions with a high VEI. The largest of these are presented in Table 2.2, and the changes in the 533 volcanic activity events that resulted in fatalities between 1485 and 2017 can be tracked in a graph (see eruption). The Smithsonian Institution (2014) and the statistics on volcanoes of the Earth (see Volcanoes of the World) provide details of all active and once active volcanoes of the Pleistocene and Holocene ages. The volcanic eruption with the highest death toll in the last 30 years was the 2018 eruption of the Fuego volcano in Guatemala, which is still active in 2020. The figures vary widely, with 425 victims according to EM-DAT and nearly 2 million people being affected by the eruption (Fuego; CRED, 2019). Between 2008 and 2017, the average annual death toll caused by volcanic eruptions was 44, although, in 2018 alone, 878 people died because of volcanic eruptions (Fig. 2.7). Other natural hazards (e.g. floods, windstorms, extreme temperatures or earthquakes) have five to twenty times as many victims as volcanic eruptions, and the financial damage is much higher. On average, volcanoes cause $0.2 billion worth of damage per year, compared to around $70 billion per year from floods and droughts (CRED, 2018b). There are around 1500 potentially active volcanoes worldwide. Around 500 erupted in historical times, but only a third of these are active today (Volcanoes of the World; GVP, 2013; Siebert et al., 2010; Smithsonian, 2014). These digital databases are considered a valuable source of information on the Earth’s volcanism, although the data for some events are questionable (Fig. 2.8). The GVM database contains more than 600 volcanic events that resulted in fatalities, showing that, although large numbers of fatal eruptions are rare, the number of people living in regions susceptible to volcanic activity is increasing. The number of tourists visiting these spectacular areas has also increased significantly. According to Brown, more than 800 million people now live within 100 km of areas at volcanic risk (Brown et al., 2017). At the same time, the risk of these regions being exposed to the threat is reduced by professionally based preparations for protection. Direct (e.g. pyroclastic flow, lahar, gas) and indirect (e.g. tsunami, famine, volcanic ash) impacts associated with volcanic activity must be expected, which may occur with a certain delay in time. The social consequences of volcanic eruptions include social damage due to evacuation (e.g. 400,000 people were displaced when Merapi in Indonesia erupted), social and financial damage due to the shutdown of the economy, which was particularly high in the case of the multiple eruptions of Montserrat (the Caribbean, 1995). The eruptions also have direct economic damage; for example, the 2010 Icelandic eruption caused a loss of around USD 5 billion in air traffic.

Indonesia

Indonesia

Iceland

Indonesia

Guatemala

Indonesia

Tamboraa

Krakatau

Mt. Pelée

Nevado del Ruiz

Unzen

Vesuvius

Laki-Grimsvötn

Kelutb

Santa Maria

Galunggung

1.

2.

3.

4.

5.

6.

7.

8.

9.

10.

Italy

Japan

Colombia

Martinique, Lesser Antilles

Location

Volcano

1822

1902

1586

1783

79

1792

1985

1902

1883

1815

Year of eruption

VEI5

VEI6

VEI5

VEI6

VEI5

VEI4

VEI3

VEI4

VEI6

VEI7

Intensity

Stratovolcano

Stratovolcano, lava domes

Caldera, dome, stratovolcano

Caldera, fissure/rift volcano

Caldera, stratovolcano

No data

Stratovolcano, pyroclastic cone(s)

Caldera, stratovolcano

Caldera, stratovolcano, pyroclastic cone

Stratovolcano, caldera

Type and shape of volcano

23,080

29,025

36,417

~60,000

Pyroclastic avalanche

Pyroclastic flow, lahar

Lava material, tephra

Pyroclastic flow, explosions

4011

~6000

~10,000

>10,000

~13,000

(continued)

Number of casualties

Landslide, tsunami 14,524

Lahar, explosions

Pyroclastic flow

Pyroclastic flow, tsunami

Pyroclastic flow, tephra

Origin of damage

Table 2.2 Profiles of the ten deadliest volcanic eruptions and the five largest volcanic eruptions (A–E) with a VEI above 6 in the last five hundred years

46 2 Geophysical Hazards

Long Island

Huaynaputina

Billy Mitchell

C

D

E

Papua New Guinea

Peru 1580

1600

1660

1912

1991

Year of eruption

VEI6

VEI6

VEI6

VEI6-3?

VEI6

Intensity

Tephra, pyroclastic

Tephra, pyroclastic flow

Origin of damage

Pyroclastic shield, caldera

Maar, lava dome, stratovolcano

Pyroclastic flow

Pyroclastic flow, tephra

Caldera pyroclastic cone, Lava flow, tephra maar

Stratovolcano, lava domes

Stratovolcano, lava domes

Type and shape of volcano

No data

~1500

No data

No data

857

Number of casualties

are several known eruptions with a VEI7 grade from the last millennium, but there are a lot of uncertainties in the data. VEI7 volcanic eruptions include Samalas (Indonesia, 1257), Tientse (border of China and North Korea, 946), Hatepe (New Zealand, about 180), and there was a mysterious eruption in 1465 that was probably greater than VEI7, but the eruption point has not been found yet. The VEI7 volcano eruption on the island of Santorini in 1600–1650 (?) BC, which claimed 20–100,000 victims and caused severe damage to ancient settlements in the area, has been extensively analysed. Hundreds of metres of volcanic ash covered the remaining caldera, and the resulting tsunami may have indirectly contributed to the destruction of the Cretan civilisation, which was about 100 km away b According to some estimates, the 1919 eruption claimed an estimated 5000 lives Source Smithsonian (2014), Molist (2017) and Keller and DeVecchio (2016)

a There

Alaska

Novarupta

B

Papua New Guinea

Philippines

Pinatubo

Location

A

Volcano

Table 2.2 (continued)

2.1 Natural Hazards Posed by Volcanic Activity and Mitigation Options 47

48

2 Geophysical Hazards

Fig. 2.7 Number of volcanic eruptions by country between 2000 and 2019. Source CRED (2019)

Fig. 2.8 Distribution of Holocene volcanoes and those with fatal incidents recorded since 1500 AD (after Brown et al., 2017)

2.1.4 Relationship of Volcanism to Other Natural Hazards Volcanic activity can also create other natural hazards. For example, it can contribute to the outbreak of fires, where volcanism is not the primary generating process, but, understandably, hot molten rock that erupts during volcanic activity can cause fires. Another such link emerges with earthquakes. Earthquakes not only play an important role in volcanic eruptions (they predict them), but they also occur because of the eruption. Volcanic-induced landslides are typical after an eruption, of which lahars are good examples. Among the fatal eruptions is the 1883 eruption of Krakatoa, but most of the victims were not killed by the pyroclastic flow but by the earthquake and tsunami caused by the collapse of the caldera (and the displacement of water) that accompanied the eruption.

2.1 Natural Hazards Posed by Volcanic Activity and Mitigation Options

49

Finally, there may be a link between volcanic activity and climate as well, as eruptions can cause temporary or more permanent climate fluctuations. A good example is the 1815 eruption of Tambora when the Earth’s average temperature decreased by 0.4–0.7 °C and the coldest summer in historical times occurred. The 1991 eruption of Pinatubo released 20 million tons of sulphur dioxide into the air, the aerosols of which, while moderating global temperatures, increased winter temperatures.

2.1.5 Forecasting and Mitigating Volcanic Hazards The action line for reducing the impact of volcanoes consists of a series of steps that can be separated in time. Planning, forecasting and monitoring are the key to protection, and all indicate that the most important tasks are those to be done in the preparation phase before an incident. This phase of professional preparation includes the analysis of previous eruptions, the analysis of the hazard and its mitigation options, the education about it, the modelling of the probability of an eruption, the mapping of the areas at risk of an eruption, the integration of the operational monitoring system and the decision-making process, the communication of the forecasts, the complete system for the management of a possible evacuation, the appropriate level of warning and its explanation. Overall, these issues can include in planning, but the planning process is much broader since, for example, the design of buildings can also include in this group (USGS6). A monitoring system must be set up at this stage, and evacuation routes must be provided. The operation of the monitoring system, or the construction of buildings and dams to divert any lava flows, will also be extended into the eruption period. Warnings should be issued about the concentration of gas and ash, which could pose a serious health risk in the event of an eruption, and about the possible formation of mudslides. During the period after volcanic activity, which is generally slow to stop, the cautious use of networks (e.g. water, electricity) is recommended because of the risk of failure. However, systems may take several months to restore normal operation (USGS7).

2.1.6 Monitoring Volcanic Activity Monitoring methods are a cost-effective way to identify hazards associated with volcanic activity. When interpreted comprehensively, the information obtained can save lives first and foremost. Still, it can also improve the resilience of the affected population by helping to prepare for evacuation, maintain certain elements of infrastructure (e.g. communication network) or support the management of increased health risks. The eruption and its impact depend on many factors, and the forecast is very uncertain, yet there are several foreboding signs. Therefore, any data can be useful, regardless of whether they come from real-time systematic data collection or from

50

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campaign data collection resulting in data of lower value. It is also worth bearing in mind that 40% of the adverse effects of a volcanic eruption occur in the first 24 h, so mitigation is also possible at this time (Loughlin et al., 2015). About a hundred observatories, institutes and international organisations measure and monitor volcanic impacts (e.g. WOVO = World Organization of Volcano Observatories; IAVCEI = International Association of Volcanology and Chemistry of the Earth’s Interior). The rationale for these monitoring activities is that measurable signs can provide a basis for predicting volcanic hazards and issuing warnings. At the same time, identifying the signs of eruption is the best-known method today for predicting danger and planning protection. A volcanic eruption is indicated by several geographical phenomena that can be traced back to the upward movement of the magma that supplies the erupting lava. The most measurable signs are earthquakes and the associated increased seismic activity (Phillipson et al., 2013). This information can be used, within certain limits, to predict the movement of magma, the location of the eruption and the intensity of the eruption. One problem is that a single geophysical measurement can only predict the location and intensity of an eruption with a certainty of about 50% (Loughlin et al., 2015). At least four seismometers are needed to determine the location of the eruption. Still, these are not always available, so the use of lower-cost instruments (e.g. satellite data) has become common. Monitoring can also use the fact that the surface is deformed before the eruption. These surface bulges are formed by the upward movement of magma at a rate of mm-dm/year. Unfortunately, surface rises are not very efficient because, for example, satellite images (Sentinel) are only available every five to six days; data from the same surface are relatively rare, so the temporal resolution is not at the same scale as the process. Therefore, GPS field measurements with an accuracy of cm have become the most used method. Further signs of eruptions are changes in the gases and water vapour leaving the volcano. These are related to the upward movement of the magma because the gases in the deep magma are precipitated due to the pressure drop caused by the upward movement of the magma, i.e. the more magma moves towards the surface, the more intense the volcano’s gas emission becomes. When exposed to sunlight, these gases can combine with moisture and oxygen to form aerosols, acid volcanic smog or vog, hazardous to health. This gas content can be dangerous to wildlife even if the volcano does not erupt (Hyndman & Hyndman, 2017). Although carbon dioxide is part of the air, its high molecular weight means it can accumulate in depressions, and its concentration can be life threatening. The example of the Merapi volcano (Indonesia) highlights the importance of monitoring. The eruption of this volcano in 2010 was predicted by five hundred minor earthquakes, and the imminent eruption was also indicated by the high levels of SO2 , H2 S, CO2 and HCl in gas seepage samples taken from the top and sides of the volcanic cone (Surono et al., 2012). The changes in the CO2 /SO2 and CO2 /HCl ratios and the increase in the concentration of these gases were particularly revealing. It was partly as a consequence of this dangerous air quality condition that the evacuation of some 400,000 people was carried out, which was further justified by the dust load released into the air during the volcanic eruption.

2.1 Natural Hazards Posed by Volcanic Activity and Mitigation Options

51

The increase in SO2 concentration significantly increases the volcano’s explosivity, so it is not by chance that there is continuous satellite monitoring of sulphur dioxide (NASA, 2020). An important element of monitoring could be the preparation of a heat map of volcanoes. This map can indicate the temperature increase associated with the approach of magma to the surface, changes which can predict the instability of the volcano’s state or its eruption. At present, remote sensing methods provide these data on a daily basis at most. Today, heat map monitoring is organised to cover about 200 volcanoes, some of which are available in near real time in the databases provided previously, and in some cases, they are available in near real time. Volcano monitoring can also include other factors in addition to the three basic parameters, i.e. earthquake, surface elevation and increase in the concentration of eruption-related gases. These include, for example, changes in groundwater levels or soil geochemistry, measurements of electrical conductivity and magnetic anomalies on and around the volcano. These all improve the certainty of the forecast.

2.1.7 Issues Related to Forecasting Volcanic Eruptions Volcanic eruptions cannot be predicted precisely in time or space, and it is also uncertain whether they will erupt at all. It is not helpful enough to analyse previous eruptions in detail, but we can use them to mitigate the adverse impacts more effectively. Perhaps the most significant issue in achieving mitigation is the possible prediction of an eruption. Providing the start of the eruption and an indication of changes in the affected area provides the information that allows the most important element of mitigation, i.e. early warning, to be issued. Despite the increasing availability of instrumentation for monitoring and forecasting systems, it is still impossible to determine the exact pace of volcanic activity, especially for smaller eruptions, which are difficult to predict. Considerable progress has been made in the operation of monitoring systems to reduce this uncertainty. There are now hundreds of volcano monitoring centres in a network, providing real-time and near real-time volcanological measurements. These early warning systems helped organise the timely evacuations related to the volcanic eruptions in Mexico in 2000 and Indonesia and Iceland in 2010. These real-time warning systems are important for the safe operation of aircraft, as 129 of the 247 active volcanoes known since 1950 have produced large amounts of ash that have jeopardised air travel. Still only two serious aircraft accidents have occurred since then. Long-term forecasts generally rely on the past activity of volcanoes and are based on historical and geological evidence.

52

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2.1.8 Technical Tasks Related to Reducing Volcanic Damage The most obvious way to reduce damage is to have early warning systems in place. However, due to the limitations of predictability, in half of the cases, they are not suitable for these tasks, so other methods must be used to reduce the impact. For lava flows, slowing down, diverting or cooling them could be possible solutions, but in practice, these have had limited success. Slowing of lava flows is used in most cases, but also dams and diversion channels can help to change the lava track (e.g. the fluid lava of Mauna Loa is channelled this way). One of the deadliest processes in volcanism is lahars, and there are adequate early warning systems in place. These can provide enough time (possibly several hours) to allow sufficient time for evacuation in the affected area. Avoidance of the lahar hazard has already been successfully achieved in numerous locations (Hyndman & Hyndman, 2017).

2.1.9 Human Tasks Tackling to Mitigate the Impact of the Hazard The social impact of volcanic eruptions is determined not only by the type of volcano but also by the vulnerability of the population exposed to the hazards. Based on the predictions collected, it is useful to gather as much information as possible to reduce the impact of the volcano and, thus, indirectly, the vulnerability. To this end, it is also important to analyse the social conditions, i.e. how prepared and committed the people involved are to mitigate the impact and how effective the state and local authorities are as managers. The analysis of the databases shows that the frequency of eruptions is not increasing, but the hundreds of millions of people living in areas at risk of eruption, sometimes out of necessity, and the social and cultural problems increase their vulnerability (Barclay et al., 2015). The only effective way to reduce the vulnerability of society and the risk is to evacuate areas where pyroclastic flows are likely to occur before an eruption. However, having an evacuation plan is not sufficient to reduce vulnerability, as its success requires broad social cooperation, supported by adequate training and information of affected people (USGS6). To reduce the impact of hazards on society, IAVCEI is available at the regional level, while the UN Office for Disaster Risk Reduction (UNDRR) or the Global Volcano Model (GVM) assists the work at the global level. However, in addition to these, most of the responsibilities and tasks belong to local authorities and regional government units, which are responsible for managing the hazard, providing effective information, organising evacuation, and providing professional and organisational information to those affected. One of the key elements in reducing volcano hazards is credible and professional communication. If this is weak, it can lead to a loss of trust in leaders (Barclay et al., 2008). To achieve a successful solution, risk mitigation programmes related to

2.2 The Earthquake Hazard

53

volcanic activity should be presented in conjunction with other natural hazards and phenomena (e.g. climate change), not forgetting that the aim is to reduce impacts and vulnerability to the hazard.

2.2 The Earthquake Hazard 2.2.1 Naturally Occurring Earthquakes and Their Spatial Aspects The simple answer to what causes earthquakes—one of the most serious natural hazards, but one that is well documented—is that they are faults in geology. On a global scale, the driving forces for the formation of faults are the rock flows within the Earth, which move the 60–100-km-thick tectonic plates covering the Earth’s surface through the mantle material, which behaves fluid like under certain conditions. These motions affect not only the plates but also the microsized plate fragments that detach from them. Thus, the accumulated tension in the rocks and the energy released from time to time is the major cause of earthquakes, which can also be caused by further sudden shifts. Faults can be related to plate movements, such as the subduction of plates or microplates (e.g. the complex Alcapa or Tisza/Tisia Plates in the Carpathian Basin), and their divergence from each other (e.g. the Mid-Atlantic Ridge). In addition, these plates can slide past each other, a phenomenon known as a transform fault. These plate motions can generate faults due to the high energies they carry. An often-cited example is the 1960 Chilean earthquake associated with subduction, the largest earthquake ever known when the oceanic plate dived beneath South America’s continental plate. The earthquake was so strong that it caused a relative height difference of 10 m in the affected settlements. Earthquakes are linked to tectonic plates in 90% of cases, but more minor earthquakes can also be triggered by other causes. Earthquakes can have a lithological cause (e.g. compaction in sedimentary rocks), but they can also be caused by anthropogenic effects (e.g. mining, reservoir operation). For the latter, some authors identify three main causes: (a)

(b)

(c)

If the reservoir is created by damming the valley, the huge mass of rock layers under the water can be weakened and compacted by the pressure of the water, resulting in frequent tremors of up to 4–5 M. The injection of wastewater can cause earthquakes of similar magnitude into deeper sediment layers (e.g. in the USA in 1962) or the collapse of underground reservoirs of mined materials (e.g. water, hydrocarbons). Underground nuclear explosions (not allowed since the late 1960s).

The list may be extended to include many other small but anthropogenic quakes of small magnitude, either related to mining or for professional–scientific purposes.

54

2 Geophysical Hazards

The refraction or reflection of artificially generated quake waves is measured, taking advantage, for example, of the fact that one type of wave does not travel in an aqueous (petroleum) environment so that artificial quakes can be used to explore subsurface resources (Keller & DeVecchio, 2016). There are, of course, different stages in the development of faults: there are times when these geological formations are still elastic and reversible (e.g. due to high pressure or temperature), and there are times when they are part of a plastic, but an irreversible process, and once a physical threshold is reached, a fault occurs. For the above reasons, quakes are well defined along plate boundaries or subductions or associated with mid-ocean ridges or transform faults. These are among the most common narrow zones of earthquake occurrence, also associated with volcanism. More than two-thirds of earthquakes are triggered around the Pacific Plate globally. At the same time, one-sixth of them are related to the Alps-Himalayas belt stretching from the Mediterranean Sea through Turkey, Central Asia, China and Indonesia. 7% of quakes are associated with mid-ocean ridges (foldrenges.hu). Fourteen of the twenty largest earthquakes on Earth occurred at the perimeters of the Pacific Ocean (USGS, 2020). Figure 2.9 illustrates the spatial distribution of earthquakes that are not connected to a plate boundary using the Carpathian Basin as an example. The earthquakes occurring here are of relatively lower magnitude and that the Carpathians and the Julian Alps are more active tectonically than the basin itself, which is filled mainly with loose sediments.

Fig. 2.9 Spatial distribution of earthquakes in the Carpathian Basin between 456 and 2016. Source georisk.hu

2.2 The Earthquake Hazard

55

The importance of seismic waves is not only due to their sometimes-devastating consequences and the severe human and financial damage they cause. They provide useful data for determining the phenomenon’s location and “strength” and managing the consequences. When earthquakes occur, a group of waves travels through the Earth’s crust. One of these generates vibrations parallel to the direction of propagation and travels forward in a densifying and diminishing (compressional) motion. This motion is longitudinal, the fastest of the waves, with a speed of 5–6 km/s and is, therefore, the first to arrive at a given point (hence the symbol P, primary wave). In the other transverse wave, the particles move perpendicular to the direction of propagation. During their propagation, only shear forces occur in a given material, and they appear as a transverse wave (e.g. a sinusoidal wave). They are about half as fast and therefore arrive later, secondarily, denoted by S (secondary) (Fig. 2.10). Earthquake waves are reflected at the Earth’s inner layer boundaries, limiting their propagation. Still, they can also be a major aid in exploring the Earth’s geological structure, as S-waves do not travel in fluids and can therefore help in exploring, for example, petroleum.

Fig. 2.10 Calculation of the epicentre distance and earthquake magnitude based on the body waves of the earthquake, based on Wicander and Monroe (2009) (see text for detailed description)

56

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Another large group of seismic waves are surface waves. These are the waves arriving at a particular point at the latest, where the particles move along a vertical ellipse in the direction of propagation (but in the opposite direction to the propagation). They usually produce the largest oscillations. The island of Heligoland (North Sea) is mentioned in connection with surface tremors because it was the site of the largest non-nuclear detonation of thousands of tonnes of Second World War munitions in 1947. The propagation of the seismic waves generated by the explosion was measured with 18–20 instruments, making it the first scientifically designed measurement of wave propagation.

2.2.2 Measuring the Location and Magnitude of an Earthquake Epicentre Based on the knowledge of the propagation of the waves presented, it is possible to determine the quake’s location in the interior of the Earth (hypocentre) and across the surface (epicentre), the latter being the area where the most significant damage occurs. Different methods are known to calculate the epicentre location. Data from several stations measuring the seismic waves are needed to determine the epicentre. Only a very rough estimate of the location can be obtained from data from a single station. The exact arrival times of the P and S-waves recorded by the seismographs at the stations must be known for the measurement. For example, Fig. 2.10 shows a difference of 24 s between the arrival times of the S and P-waves, which indicates a distance of 215 km between the measurement point and the epicentre. Suppose we can perform this calculation using at least three measurement points. In that case, we can mark the most probable location of the epicentre at the intersection of the circles around them (see epicentrum, foldrenges.hu). The magnitude of an earthquake is usually given by two specific parameters. The first is the (destructive) impact on the wildlife/living environment and infrastructure (typically buildings). The related Mercalli–Cancani–Sieberg scale (MCS), based on empirical data, has a centuries-old history. It classifies the consequences of earthquakes into 12 categories, ranging from the imperceptible (Not felt/Category I), through the strong impact (e.g. chimney falling; Category VI), to the catastrophic, total damage (Category XII). Essentially based on this system, the European Macroseismic Scale (EMS), also with 12 divisions and similar content, has been developed and used in European countries since 1992 (see foldrenges.hu). The quake’s magnitude can be expressed as the intensity of the effect on the living and non-living environment. Another system devised by Richter expresses the magnitude of a quake in energy (or can be converted into energy). The calculation procedure is illustrated in Fig. 2.10. The magnitude (M) of the earthquake can be determined by calculating the distance from the epicentre on a logarithmic scale and based on the maximum amplitude, as shown here in a nomogram structure. For magnitude values, 1 unit, for example, represents a tenfold difference between

2.2 The Earthquake Hazard

57

the step from 2 to 3 (because the scale is exponential), but if this is converted to (released) energy, the step is 32 times greater per unit (Hyndman & Hyndman, 2017; foldrenges.hu). The magnitude (ML) can be interpreted in several ways. The traditional Richter calculation uses the following formula: ML = log A + 2.56 log D−1.67 where A is the amplitude of the measured P-wave in micrometres and D is the distance in km between the epicentre and the recording (this can be used up to a distance of about 600 km and underestimates the magnitude significantly for larger quakes (M > 8)). In addition, the magnitude can be calculated separately for more distant quakes, or it can be calculated from the physical size of the fault generated during the earthquake and the amount of energy released as a seismic wave. Among the largest earthquakes, the magnitude of the T¯ohoku quake that struck Japan in 2011 and caused damage in Fukushima was 9.1. The eruption of the Krakatoa volcano had a similar magnitude of about 56 billion kg of explosives, while the 1960 Chilean quake was equivalent to the explosion of more than 3000 billion kg of explosives (Fig. 2.11).

Fig. 2.11 Relationship between the magnitude of some typical earthquakes and the accompanying energy release. Source USGSgov

58

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2.2.3 The Frequency of Earthquakes and Their Regional Aspects Several databases are available to analyse the annual occurrence of earthquakes. Almost all countries have seismographs capable of measuring earthquake acceleration in three directions, and countries operate networks of seismographs. Thus, the epicentre of each quake and the magnitude of the quake can be precisely determined from the recorded waves. In several countries, these data are available in real time. Even on a global scale, the USGS (2020) records the location and hypocentre of all quakes larger than 2.5 M on a map (a few minutes after the quake). Similarly, the European-Mediterranean Seismological Centre provides global data on earthquakes greater than 2.0 M, covering one year (EUEQ). The speed of data supply is shown by the fact that at the time of writing these lines (at 13:58 on 17 May 2020), the data of the 2.0 M quake that occurred in Nevada at 13:44 on the same day and the 5.0 M quake that occurred in Tonga at 13:49 were already available. Several automatic seismographs also detect earthquakes in the Carpathian Basin, and the data are automatically processed and published online. Quakes of much smaller magnitude are typical, although undetectable movements below 1.5–2 M are also common. The perceptible ones are between 100 and 120 per year, with only four or five earthquakes reaching a magnitude sufficient to cause minor damage, while strong, very damaging earthquakes with magnitudes of 5.5–6.0 occur every forty to fifty years (foldrenges.hu). A wide range of archival data is available to analyse the number and characteristics of earthquakes. Therefore, a lot of information is known. The two sources in Table 2.3 rely on the same database of the US Geological Survey, so the differences are due to the length of the period considered. The table shows that still-perceived tremors occur on an hourly basis and are mainly related to different types of tectonic plate movements. It is difficult to say from this whether the number of detected quakes is high, but it can be concluded that it is possible to prepare in good time for earthquakes resulting in high human and material losses so that the social consequences can be reduced. Table 2.3 Observed frequency of earthquakes on Earth Average M

Average annual occurrence between 1990 and 2010

Great

+8

1

Major

7–7.9

15

String

6–6.9

134

Moderate

5–5.9

1319

Light

4–4.9

13,000 (estimate)

Minor

3–3.9

130,000 (estimate)

Very small

2–2.9

1.3 million, 150 per hour (estimate)

Source eqstats and Keller and DeVecchio (2016)

2.2 The Earthquake Hazard

59

The largest earthquakes of the last hundred years can be linked to tectonic plate boundaries (see Fig. 2.2). More than 10,000 strong earthquakes exceeding 6.0 M have been recorded in the last 100 years. According to archival data, the 20 largest earthquakes of the last century were all greater than 8.4 M. The largest to date was the 9.5 M as mentioned earlier quake in Chile in 1960. Still there were also earthquakes with serious consequences in the last decade: in Chile in 2010 (8.8 M), in Sumatra in 2012 (8.6 M) and in Japan in 2011 (9.1 M) (major earthquakes). In the last case, not only the earthquake, which occurred about 100 km off the coast of Japan, but also the resulting tsunami wave caused serious damage. The obvious question is whether these data might indicate a possibly significant change in the number of earthquakes (eqstats). The long-term time series data suggest that the change in earthquake frequency is probably random and that the value of the changes so far is part of the normal fluctuation (Herman et al., 2015). The perception that the number of earthquakes has increased may be because the flow of information has accelerated significantly in recent decades, and the population has also increased in potentially affected areas. However, there is no geophysical cause that would change the frequency of earthquakes. The question that people are asking is also about the future number and predictability of earthquakes. The long-term answer is known because the movement of the tectonic plates varies over millions of years. For example, the African Plate has been approaching the Eurasian Plate at a rate of around 4–10 mm/year for tens of millions of years, one consequence of which was the disappearance of the Tethys Ocean (replaced by the Mediterranean, which is no longer an ocean floor). The Mediterranean region, stretching from the Azores through Anatolia to China, is known to have a system of faults, fractures and tectonic trenches that have been well-defined earthquake sites in the past (Fig. 2.12, Herman et al., 2015; Pollitz et al.,

Fig. 2.12 Location of the Anatolian fault and the associated major earthquakes marked with an asterisk and the year of occurrence (based on Stein et al., 1997; USGeosci)

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2014). In the longer run, the Pacific Plate is also predicted to be associated with the currently emerging faults and earthquake nests related to tectonic systems (Zhang et al., 2018).

2.2.4 Impacts of Earthquakes 1.

Social Impacts

Earthquakes are one of the natural hazards that cause the most casualties. From 2008 to 2017, there was an average of 26 major earthquake events per year, while in the last 20 years, there were 563 major earthquakes (major in terms of human and financial impacts) recorded. Between 1998 and 2017, records show that 125 million people were affected and 724,234 deaths were reported (CRED, 2019; Wallemacq et al., 2018). These quakes represent more than half of all-natural hazard casualties. The number of casualties is not necessarily (and only) related to the magnitude of the earthquake but the condition of the environment of the affected population (Table 2.4). The fatal earthquake on record occurred in 1566 in Shaanxi, China. The quake devastated a zone of more than 600 km and caused the deaths of up to 60% of the population of some provinces. The reason for this large number is that the majority of the population lived in multi-storey cave dwellings (yaodongs) carved out of loess cliffs in a tradition dating back thousands of years. These collapsed, killing more than 800,000 people. Recent calculations have estimated the quake at 7.9 magnitudes and classified it as a category XI earthquake (EMS). Although Table 2.4 Eleven earthquakes that claimed the most lives Year of earthquake

Location

Estimated death toll

Estimated magnitude

1556

Shaanxi (China)

830,000

8.0

2010

Haiti

100,000–316,000

7.0

1976

Tangshan (China)

Officially 255,000

7.5

1920

Kansu (China)

273,400

7.8

526

Antiochia (Byzantine Empire)

250,000–300,000

7.0

115

Antiochia (Roman Empire) 260,000

No data

1138

Aleppo (Syria)

7.1

230,000

2004

Indian Ocean (Indonézia)

227,898

9.1–9.3

1303

Hongdong Mongol Empire (China)

200,000

8.0

856

Abbasid Caliphate (Iran)

200,000

7.9

1780

Tabriz (Iran)

200,000

No data

Source usgsregional, archivdata; iris; damaging earthquakes, usgsdata

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China recorded earthquake hazards as early as 132 AD, this disaster illustrates the limitations of preparedness. In addition to the immediate short-term effects on people, earthquakes also have long-term effects, including homelessness, water scarcity, social insecurity and related social consequences (Bryant, 2005). The social consequences depend highly on economic opportunities, especially in countries with lower economic capacity. It is a negative trend that, although there are numerous state responsibilities, ranging from deforestation to ensuring the stability of slopes, many of the adverse consequences stem from the state’s declining role in damage control and an increasing number of people being driven towards private insurance (Wisner et al., 2012). 2.

Economic Impacts

The financial damage caused by earthquakes goes beyond the damage and destruction of infrastructure; it can lead to everything from the closure of businesses to the withdrawal of investment and, finally, to the inability to function the entire economy. Between 2008 and 2017, the direct and indirect financial damage caused by earthquakes was the third highest after windstorms and floods, causing billions of US dollars’ worth of damage. Some countries were particularly severely affected: in Armenia, for example, the damage amounted to 3.5% of the country’s annual GDP, while in Haiti, it was 17.5% (CRED, 2019). Over the past twenty years, the damage caused by earthquakes was estimated to be 661 billion dollars, which is about a quarter of all-natural damage (Wallemacq et al., 2018). Of course, when you consider that the 2011 T¯ohoku earthquake east of Japan itself caused $228 billion in damage to the Fukushima nuclear power plant, the high damage value is understandable. It is considered the most damaging of all-natural hazards (MURe). 3.

Environmental Impacts; Relationship with Other Natural Hazards

Similarly, to other natural hazards, earthquakes can trigger new hazards and other processes. Examples include tsunamis, discussed in detail later in this chapter (see Sect. 2.3), or landslides, which are the most common consequences of tectonic faults and can occur in multiple waves (Keller & DeVecchio, 2016). A very specific consequence is the liquefaction of the surface (thixotropy), a phenomenon where loose sedimentary layers lose their stability and act as fluid due to earthquakes typically greater than 5.5 magnitude, leading to the collapse of entire building blocks (Earle, 2019). The orographic consequence associated with major earthquakes can be a rise in the surface (up to 10 m), which can accelerate the risks associated with increased erosion, while the subsidence of the surface can increase the area and level of floods and can alter the coastline. In addition, changes in groundwater levels (e.g. lower groundwater levels) can cause serious ecological damage, for example, in coastal areas. There are also environmental consequences when, because of an earthquake, electricity and/or gas lines break, leading to a fire hazard.

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2.2.5 Mitigating the Impacts of Earthquakes and Responding to Hazards There are several solutions and suggestions to reduce the impact of earthquakes, both at the community and individual level, due to the significant human and economic damage. It is no coincidence that this is the most important goal of earthquake management, and this compilation aims to support this goal. The methods and proposals available are very diverse. On the one hand, they can be grouped according to whether these procedures should be implemented before, during or after the event. This compilation focuses on the activities proposed to be carried out before the occurrence of a hazard, while the tasks to be carried out during and after the occurrence of a hazard are summarised in Sect. 1.5. The methodological and theoretical basis of the preparations also aims to ensure that the affected community is prepared in some way to mitigate the effects of the hazard/disaster. Although long-term forecasts of this kind do not directly help people in a given region, adverse effects can be mitigated by preparing for such events. Therefore, the continuous monitoring of quakes is necessary. 1.

Earthquake Hazard Mapping

It is essential to delineate and map the areas affected by earthquake hazards based on available information in the preparatory phase. An earthquake hazard map, which can be produced following the USGS methodology, indicates the probability of aboveaverage earthquake intensities on a 50-year average. The propagation velocity and its acceleration value (relative to g) are considered to determine the magnitude of an earthquake. For example, Fig. 2.13 shows the probability of the acceleration of the predicted event exceeding the frequency value measured over the last 50 years (the standard timescale for determining the average value). In the case of the figure, an acceleration of about 3.5 m/s2 represents about 34% of the value of g. The damage caused by earthquakes depends on several geological and geophysical factors in addition to velocity, but this is the logical basis for the earthquake hazard map (USGS9). The frequency of earthquakes overtime is regulated by Poisson’s law, which can be used to find the annual exceedance rate over fifty years. Most systems use this to determine the expected occurrence of an earthquake hazard. Thus, earthquake hazard mapping is not just a record of a state or past events but also a forecast (deterministic for frequent earthquakes, otherwise mostly calculated with a probabilistic model). The calculation requires the use of several basic pieces of information, such as data from past earthquakes. Future earthquake hazard values need to be mapped based on the baseline data and the model used (e.g. NSHM—National Seismic Hazard Model in the USA). The factors hindering the propagation of earthquakes (e.g. petrological composition) need to be recorded and how the magnitude of the earthquake varies over distance (Keller & DeVecchio, 2016). Values and parameters calculated according to similar relationships are also used to produce relevant maps for other countries. For most regions, such information

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Fig. 2.13 Acceleration of 3.5 m/s2 causes an increase in g of about 34% (must be calculated with a value of 9.81 cm/s2 ). Source USGS9

is available independently. For example, this data is also available separately for each state in the USA, not only for the whole country (see Earthquake Hazards). Figure 2.14 shows the earthquake hazard at EU NUTS3 resolution at the regional scale. The highest earthquake hazard values are in the southeast of Europe, Greece, Romania and Italy. This fact is explained by the microplate fault system detailed in Sect. 2.2.1. The same principle of the general method has been used to develop earthquake hazard models for other regions. The earthquake hazard map of the Carpathian Basin (Fig. 2.15) shows the low-intensity seismic movements of the last decades but does not indicate large-scale plate boundary transform faults. According to its geological characteristics, the basin is at low risk. 2.

Global Earthquake Model (GEM)

Over 90% of earthquake victims in the last 50 years have come from developing and poorer developing countries. At the same time, developed countries accounted for almost two-thirds of the damage costs, while only a few per cent of the victims were from these countries. These data underline the important fact that if the right information on earthquakes is available, numerous mitigation measures can be taken in advance, and human lives can be saved. One of the essential pieces of information for taking preventive measures is to know the spatial variations of the earthquake hazard. An example is the USGS earthquake hazard map described earlier. Such information is particularly important for less developed countries, which lack the resources to measure earthquake hazards and risks. Thus, the Global Earthquake Model (GEM), which is the first digital earthquake hazard and risk map of the world, was developed at the suggestion of the OECD

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Fig. 2.14 Potential earthquake hazard of European regions, classified into five categories. Source Espon (2004)

(Pagani et al., 2018). The GEM can provide particularly important information for regions severely affected by earthquakes, providing a basis for increasing earthquake safety, reducing the physical consequences and financial impacts and accelerating reconstruction (Fig. 2.16). The Global Earthquake Model is a risk model developed by international organisations and private companies in 2007 (GEM; MunichRe, 2017). It aims to produce and continuously update an earthquake hazard map for all countries, enabling them to estimate the potential for damage, the effectiveness of mitigation measures and the increase in safety.

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Fig. 2.15 Earthquake hazards in Hungary. Source seismology.hu

Fig. 2.16 Global earthquake hazard map of the Earth (Pagani et al., 2018)

The data from the Global Earthquake Model can be compared globally with the number of people living in an earthquake-prone area, their economic potential and the relative cost of recovery or insurance concerning the region’s GDP. As about 2.7 billion people live in earthquake-prone areas, this population figure also justifies the development of GEM, which provides information that can be used to plan prevention measures more easily (Shi & Kasperson, 2015).

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Earthquake Prediction

Due to the propagation speed of seismic waves and the uncertainty of earthquake occurrence, only short-term forecasts could play a role in earthquake predictions. An essential condition for successful prediction is accepting that the preconditions can be considered an important basis for the event’s occurrence. Such preconditions could be, for example, the widening of cracks and faults (e.g. by GPS measurements), changes in the speed of seismic waves or even a logical sign might be a decrease in groundwater levels or the release of radon gas. The movement of the surface, its rising and subsiding spots and changes in slope are often investigated as possible preconditions. In the past, the unusual behaviour of certain animal species, especially in Japan and China, was also analysed. The significant increase in the number of foreshocks and small quakes also seems significant. In other words, many signs suggest that they can be used to predict quakes with certainty. However, the process is influenced by several factors, and these predictions only show a measurable relationship for individual segments. A good example of this uncertainty is the prediction of the February 1975 Haicheng (7.4 M in China) earthquake, analysed in great detail by experts. Although there were several simultaneous predictions, many forecasts were considered to prepare for the quake, for example, by ordering the evacuation of the settlement of a hundred thousand inhabitants (Wang et al., 2006). However, the uncertainty of the forecasts is illustrated by the fact that a year later, a magnitude 7.6 earthquake struck the Chinese city of Tangshan without warning, killing at least 255,000 people, according to the news. According to Uyeda, Japan did not accept that the predictions as a prerequisite for an earthquake would provide credible information and instead sought to improve seismology infrastructure (Uyeda, 2013). This approach, typical since the 1960s, only changed short-term forecasting after the 1995 Kobe and 2011 T¯ohoku earthquakes. In the USA, for example, a GPS of more than 200 sensors located along the St. Andrew fault in Los Angeles, which is highly sensitive due to its high population density, monitors changes in the fault system, which is only one of the signs of a potential earthquake. Although it is impossible to say exactly where and how big an earthquake is likely to occur, there are other ways of estimating an earthquake’s local and temporal probability beyond the warning signs. These include, for example, the analysis of past earthquakes to provide more accurate information on expected plate movements. Some monitoring systems analyse the frequency of smaller faults along the main faults, which can predict the location and time of a future earthquake. More recently, an attempt has been made to estimate the threshold of energy accumulation based on the seismicity gap. This approach assumes that if an active fault zone is quiescent for a longer period, tension accumulates there and is resolved in a quake after a threshold point. It is also possible to calculate the return period of an earthquake (for a given time interval) on a probabilistic basis and therefore estimates the probability of reoccurrence (again using the example of Los Angeles, for example, a return period of 22 years was calculated after the 2004 earthquake: Hyndman & Hyndman, 2017).

2.2 The Earthquake Hazard

4.

67

Early Warning Systems

One of the most effective means of reducing the undesirable effects of natural hazards is early warning systems. In the case of earthquakes, this is a rather limited method, although it is used in several countries. The underlying idea is based on the different speeds of earthquake waves and radio waves. The first earthquake waves to arrive, the P-waves, cause less damage than the S-waves, which have half the speed (but still a few km/s). This difference gives a few seconds of preparation time depending on the distance. Calculations by the USGS suggest that at about 300–500 km from the epicentre, approximately 50 s are available to act. On the other hand, seismic waves are generally of lower speed than radio waves (on which the warning can be transmitted), so an average of 30–50 s is available for warning altogether (USGS9). This difference is very short, even if today, ambulances, fire brigades, etc., are automatically alerted based on the detections. In most countries affected, national programmes to manage earthquake hazards are completed. In these programmes, mitigation actions are based on the impacts or modelled risks of measured earthquakes (see GEM). A common one is to use the HAZUS model, which considers dozens of other factors in addition to the magnitude of the earthquake (FEMA, 1999). This multidimensional model can also be interpreted as a kind of cost–benefit analysis. 5.

General Earthquake Mitigation Tasks

Education about the dangers and consequences of earthquakes and personal preparedness is a well-defined task in many countries. Information can be provided to potentially affected people, but the basic effects of an earthquake can be explained, and people can be motivated to reduce the possible consequences or take personalised action. Regular information should be provided as widely as possible on the ways and means of dealing with the hazard, the objectives to be achieved and the methods used. Earthquake recovery usually involves significant financial damage. Therefore, ensuring earthquakes separately in affected areas is common (but not common enough). Indeed, most homes must have home insurance, but this does not usually cover the full cost of earthquake damage. For this reason, “investing” the additional cost of property insurance can be a significant help, particularly in affected areas. However, a combination of the last modification of infrastructure, buildings and human preparation can significantly reduce damage. In California, for example, predictions for the next thirty years give a 99% probability of earthquake values above 6.7 M and a 46% probability of over 7.5 M so that earthquake insurance may be particularly appropriate in this state (Keller & DeVecchio, 2016). 6.

Individual Preparations for an Earthquake

Often, many people at risk of earthquakes suffer from a lack of information. Although individuals could take certain precautions on their own, they do not make any prior effort to reduce earthquake hazards. The Pareto principle is cited as an example, which states that in the case of earthquakes (and other hazards), only 20% of the

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earthquakes cause 80% of the consequences. Thus, for example, the events with an 80% probability of occurring should be prepared for rather than the unlikely events. These data also underline the importance of prior action, which can essentially be summarised by the goals of gathering as much useful information as possible about the hazard process, having an individual plan to reduce the consequences as much as possible (from escape to survival) and making all possible extra preparations. In many countries, numerous lists have been drawn up for earthquake preparedness, detailing the steps that should be taken in advance. The very simply worded 80–100 item checklist generally focuses on three objectives: to be able to survive in one’s own home without outside help for two weeks, to be able to leave one’s home (prepared) in a very short time and to be able to get to one’s home or safety as soon as possible after the disaster (emer1; emer2; emer3). The available English and German descriptions give very detailed advice on what to do if you are outdoors (e.g. move away from buildings, power lines, road signs and traffic lights) or on the road (e.g. do not park under trees, overpasses or bridges, stop during the quake). At the same time, if you are indoors, you should stay in slightly more sheltered, structurally safer places when experiencing an earthquake. All this does not exempt you from modern building design. In Japan, for example, buildings are divided into different “generations” depending on when they were built. Earthquake-resistant building structures (e.g. columns and walls) can absorb part of the seismic movements, cushion the effects (e.g. reduce the intensity by 70–80%), or built-in seismic isolation structures can reduce the intensity of the vibrations buildings by up to a quarter. As a result of their mandatory use in Japan, the magnitude of damage to buildings is extremely low, despite the strong earthquakes (see japaneq). Professional, theoretical studies on earthquake vulnerability can be used in the preparatory phase of earthquake responses before an earthquake occurs. These results may provide useful information for the population affected but can also be considered in the development of building regulations and standards. Important data are thus available for the construction of infrastructure elements and for spatial planning in general. From an economic point of view, these data can be used as essential information for calculating insurance fees, for example. Damage to infrastructure is costly, and businesses may temporarily lose their ability to generate income. At the same time, businesses often do not do all they can to mitigate the impact of earthquake hazards in advance (FEMA, 1999).

2.2.6 Some Infrastructural Aspects of Mitigating Earthquake Impacts In the preparatory phase, many investment tasks may need to be carried out that could also significantly reduce the impact of earthquakes. The most well known are those related to construction. The severe aftermath of the Tokyo earthquake of 1923 and the California earthquake of 1933 led to building regulations requiring a new

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type of performance-based engineering. The main idea was that buildings should be designed and constructed in the most resistant and safest way concerning earthquakes (Wisner et al., 2012). Many examples of its use can be cited; for example, in Japan, buildings can withstand quakes above magnitude seven without major damage. Of course, this requires considerable public support, which recognises the importance of building design while accepting that a more earthquake-proof construction method is costlier. However, it is still less than if it were done as a retrospective correction. The design and construction of buildings are therefore carried out based on building types, which, although they differ from one country to another due to different regulations, are logically identical. The earthquake resistance of the 32–36 types of buildings covered by the building regulations is interpreted separately (Wisner et al., 2012). This modern building practice is not always implemented because some authors argue that earthquakes affecting old buildings sometimes cause fewer casualties than those affecting new ones (Keller & DeVecchio, 2016). The essential infrastructure, access routes and service systems are important for industrial, commercial and residential buildings, but so is their location. Most plans achieve this by drawing up spatial zones. The location of critical infrastructure elements (e.g. hospital, school, fire station, shelters, communication system) in particular and the assessment of their necessity and capacity may be part of the preliminary action tasks. These carry important information since, for example, the status of the communication system is crucial when it comes to providing rapid and credible information to those available to respond to the alert so that they can take the necessary action in the few dozen seconds available before the earthquake.

2.3 The Tsunami Hazard—Seismic Sea Waves A tsunami is a specific, low-frequency natural hazard associated with a rapid and significant rise in ocean water levels. The tsunami phenomenon is most associated with Japan, hence its name, meaning “harbour wave”. It is also often referred to as a tidal wave, although it has nothing to do with tides.

2.3.1 Tsunami Occurrence A tsunami can be caused by several factors (NOAA). Earthquakes are undoubtedly their most common cause, so most literature includes them among the geophysical hazards. Some even treat tsunamis as a consequence of earthquakes. Other authors point out that several factors play a combined role in forming tsunamis, classifying the phenomenon as a hydrological hazard (Gebhardt et al., 2017). Even so, the most common cause of tsunamis is earthquakes, which can be caused by the subduction of tectonic plates or their displacement along a fault, as shown in Sect. 2.1.1 (Fig. 2.17). The crustal motion can cause the ocean floor to rise with the water (1a), causing the

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Fig. 2.17 Process of tsunami wave generation due to earthquakes, where arrows indicate sea-level change (own compilation)

sea surface to depress (1b), forming a displaced wave of water that rises and then forms waves as gravity tends to reach equilibrium in both directions (2) (Hyndman & Hyndman, 2017). Understandably, the height of a tsunami depends on the intensity of the quake, so for example, a magnitude eight earthquake can generate waves as high as 15 m. So, the essence of tsunami wave formation is the displacement of a large volume of water associated with this vertical movement. In general, an earthquake of at least 7.5 M can create enough space for a tsunami to form. Tsunami formation can also be linked to volcanic eruptions. This process is also associated with a significant displacement of water. Either large amounts of volcanic material are released into the atmosphere (e.g. by an eruption), and the space is taken up by water, or the volcano displaces water as it rises from the sea. However, the consequences of submarine volcanic eruptions are less well understood (although such an effect can be assumed in this case). A good example of the first tsunami caused by a volcanic eruption was the volcanic eruption on the Greek island of Santorini between 1650 and 1550 BC (Photo 2.5). Therefore, the resulting tsunami reached the island of Crete, not only destroying coastal settlements and infrastructure but also reducing the intensity of solar radiation over a greater distance due to the release of dust into the atmosphere, and the cool weather severely limited agricultural production, with serious health and humanitarian consequences. Consequently, the Minoan culture on the island of Crete was destroyed by around 1500 BC. Similar consequences were expected when the Indonesian volcano Krakatoa erupted in 1883. In that case, the island’s explosion released 18–20 km3 of volcanic material into the upper atmosphere, where it formed a dust cloud that persisted for years, causing a similar effect on the climate and resulting in the same consequences as in the previous example (in addition to the deaths of hundreds of settlements and more than 35,000 people). The process was more likely to have been similar. In this case, the volcanic material was also released into the sea during the various eruptions, displacing seawater and triggering a tsunami. This 30–40 m high tidal wave hit the coast of Sumatra, 40 km away.

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Photo 2.5 Archipelago of Santorini remained after the volcano had exploded (author’s photo)

Landslides are the third cause of tsunami occurrence. These, however, are mostly localised in the coastal zone of seas and lakes and are often triggered by an earthquake (Yalçiner et al., 2003). Such a surface mass movement was triggered by a 7.8 M earthquake in Alaska’s Lituya Bay in 1958. This movement caused a large amount of material from the former glacier wall to slide into the glacially formed bay, triggering the largest tsunami known to date, reaching a height of 524 m (see mega-tsunami). Landslide processes may also occur below sea level (submarine landslides), although little is known, especially their effects. One of the best documented is the 1929 slip of the periphery of the Grand Banks submarine plateau in Newfoundland, Canada. This slip was also triggered by an earthquake (7.2 M), and the 8–10 m tsunami wave reached Portugal, some 400 km away, and the west coast of Africa seven hours later (Tuttle et al., 2004). Another type of tsunami formation is associated with larger extraterrestrial (meteorite) impacts. Impacts of objects up to 1 km in size are rare, occurring once every 100,000 years (see Chap. 6). In such a case, when a tsunami is formed, the asteroid penetrates 4–5 km deep into the crust to form a deep hole that can absorb water, and then, with a downward mass movement, the hole is filled in, and the water is squeezed out, creating the potential for a tsunami to form (Hyndman & Hyndman, 2017).

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2.3.2 Hydrometric Characteristics and Movement of a Tsunami Wind-generated waves reach a depth of 10–30 m, are 2–10 m high and have a wavelength of 1–2 km and a propagation speed of 20–40 km/h. In the case of tsunamis, on the other hand, the entire body of water moves, with an amplitude of only 0.4– 2 m, but a wavelength of 100–300 km and a propagation speed of 500–800 km/h (Bárdossy, 2006). The parameters that are most often considered in the hydrometric assessment of the tsunami hazard are wave height, flow velocity, wavelength and wave period length. The wave amplitude of a tsunami is small, 1–2 m, in open ocean areas but can be several times larger in the epicentre of an earthquake or the vicinity of landslides. Therefore, the tsunami hazard is not located in open water but in coastal regions, where the wave rises higher as the currents slowing towards the coast are superimposed on each other. On average, the wave height can be 10–15 m depending on the topography. The explanation for this is that in shallower waters, the wavelength decreases, but the volume of water in the wave remains the same. The speed of the waves in a tsunami varies significantly with depth. In deep oceans, long wavelength motion can reach speeds of several hundred kilometres per hour (500–1000 km/h), while in shallower waters, the tsunami slows down due to friction (Fig. 2.18). Many√methods can calculate the speed (Phuong & Truong, 2012). The simplest estimate is gD, where g is the gravitational constant and D is the water depth in m. The height of the wave is used as the primary basis for calculating the intensity of the tsunami, which is also considered to be similar to the 12° EMS scale used for earthquake environmental effects (ITIS-2012 in Lekkas et al., 2013). Here, the Fig. 2.18 Relationship between tsunami wave speed and water depth (L—wavelength)—own sketch

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“height” of the tsunami at the nearest shore, calculated as a log2 function, gives values of 2.8 and 5.5 m, as well as 11 m, etc., due to the wave superimposition (Katsetsiadou et al., 2016). In addition to intensity, wavelength is also a characteristic parameter. These are different from the short waves generated by wind, which have a wavelength of 100–200 m. Tsunami’s wavelengths can reach hundreds of km, those generated by earthquakes 20–300 km, while tsunamis generated by landslides have a much shorter wavelength (ranging from 100 m to 10 km). Because of the great wavelength, the tsunami loses little energy in its motion, so it travels at high speeds in very deep water and can cover great distances at the speed of an aeroplane (Fig. 2.19). A tsunami can also travel thousands of kilometres because the long wavelength of the wave causes little attenuation, which means little energy loss. The speed of the tsunami slows down to below 100 km/h as it approaches the shallow coast. Its wavelength decreases to about a tenth of its original length (below 10–20 km), while its amplitude increases greatly. This process is the background to the destructive effect of the tsunami reaching the coast. The regions that are the most vulnerable to tsunamis are mainly the Pacific coast: Alaska and the north-western Pacific region, the Japanese islands, the Indonesian archipelago and southwest Africa (NOAA2). In these well-defined coastal areas, the tsunami return period is historically estimated to be around five hundred years (NOAA3).

Fig. 2.19 After the 2011 earthquake in the T¯ohoku region, the tsunami demolished Sendai town and spread across the Pacific Ocean. The maximum expected wave height in the ocean was about 120 cm, but it was several times higher on the coast. Source Media Commons

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2.3.3 Consequences of a Tsunami, Environmental and Social Damage On the one hand, tsunamis cause damage through the large volume of water and debris they carry. In recent centuries, the destruction of tsunamis related to earthquakes has claimed the most victims (Table 2.5). In various databases (e.g. emdat.be, munichre.com), tsunamis occur together with earthquakes or volcanic activities, so regional damage alone cannot usually be extracted from these databases. Tsunamis occurring on their own (other than those attributed to seismic and volcanic causes) have caused only a few major casualties in a small number of places and on a small number of occasions. However, earthquakes and sometimes accompanying tsunamis have caused the most deaths in this century, as coastal areas are generally densely populated. Therefore, better data can be obtained for a single year or event. For example, in 2018, twenty major incidents were recorded using a combination of earthquakes and tsunamis, two of which resulted in serious human and infrastructure losses (CredCrunch54, 2019). The most substantial damage was caused by an earthquake near Celebes (Sulawesi, in Indonesia), with an estimated magnitude of 7.5 M, triggering a mudflow, followed some 20 min later by a 4–6-m-high tsunami (Sassa & Takagawa, 2019). The death toll was 4340, making it the largest natural disaster of its kind on a global scale in the last five years (2015–2020). The tsunami warning system was operational, although it predicted a hazard with a smaller height. The tsunami devastation caused tens of thousands of buildings to suffer very significant damage and a further 30,000 to suffer moderate damage, mainly in the city of Palu (Indonesia). In the same year, in December 2018, a volcanic eruption in the Sunda Strait in Indonesia (between Java and Sumatra) triggered a tsunami, resulting in 453 deaths. The population was not warned because the tsunami had not been triggered by an earthquake. Table 2.5 Deadliest tsunamis in the last three hundred years Year

The tsunami trigger site

The tsunami occurrence site

Cause of tsunami

Number of victims

1755

Lisboa

Caribbean

Earthquake (≥9 M)

~20,000

1883

Krakatoa

Sumatra–Java

Volcanic eruption

~36,000

1960

Chile

Hawaii

Earthquake (9.5 M)

61

1964

Alaska

Alaska, California

Earthquake (9.2 M)

160

1993

Sea of Japan

Okushiri Island, Japan

Earthquake (7.8 M)

120

2004

Sumatra

Indonesia

Earthquake (9.1 M)

230,000

2011

Pacific Ocean

Japan

Earthquake (9.1 M)

20,000

Source tsunami

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Fig. 2.20 Cross section of the tsunami reaching the flooded area. Source sccoos

Although the history of tsunamis is most closely linked to Japan, the most memorable tsunami disaster in recent centuries occurred in the Indian Ocean: 230,000 people, including many tourists, died in Thailand and surrounding countries at Christmas 2004. A 9.1 M earthquake triggered the tsunami. Although the people living there were no strangers to the phenomenon, its magnitude was devastating, and the region’s early warning system was not yet in place. Among the damage caused by tsunamis, the well-documented tsunami off the east coast of Japan in 2011, following a 9.1 M earthquake, was a notable example, with subsequent measurements showing that it reached heights of up to 38 m in some places and caused severe damage even on the other side of the ocean in Chile (Fig. 2.19). In some places, the water flooded the mainland to ten kilometres (Mori et al., 2011), devastating buildings and infrastructure (Fig. 2.20). Among the environmental consequences of tsunamis, those related to flooding and erosion should be considered in particular (Keller & DeVecchio, 2016). However, the secondary effects of damage to the gas and water systems in a residential area, such as contaminated water, are also important. Contaminated water creates the potential for a range of waterborne diseases, from cholera to other bacterial diseases. Analyses of the 2004 tsunami in Indonesia and the 2011 tsunami in Japan showed that the tsunamis caused extensive damage to local populations of various coastal organisms (e.g. snails) and that coastal ecosystems had to regenerate (Miura et al., 2017).

2.3.4 Mitigation Options for the Effects of Tsunamis Preparations must be made to mitigate the effects of this specific flooding, in particular, to protect human life before the tsunami occurs. The theoretical preparation includes identifying the tsunami propagation path, gathering relevant information (e.g. infocenter, risk assessment), building a detection network, identifying critical locations, planning optimal land use for protection, designing escape routes, etc. Practical tasks, all of which can support the reduction of environmental impacts, include

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the establishment and operation of an early warning system, the implementation of protection facilities and the operation of an effective communication channel. It is not easy to separate tasks that need to be done beforehand from those that require immediate action, which is made more difficult by the short reaction time, but it also highlights the key role of prior action. Early warning of the event’s occurrence also helps reduce the impact of tsunamis. However, predicting an earthquake, a landslide or a volcanic eruption is very uncertain, so there is a time window between tens of seconds and a few minutes from the epicentre to predict the possible triggering of a tsunami; therefore, continuous monitoring is necessary. A well-functioning communication system and a wellfunctioning early warning system are needed to provide warnings in the very short time available. The global scale system was set up in 2003 and is now operated by 26 countries under NOAA’s leadership; its deployment gained real momentum after the 2004 tsunami that caused more than 200,000 deaths. The forecasting system includes sensors fixed to the ocean floor and 45 floating buoys (in the foreground of vulnerable coastal areas). These measure the passage of surges with an accuracy of cm by measuring the changes in the pressure of the water above them and transmitting the data to the buoys floating on the surface, which in turn transmit the data to satellites (see SNAMChile). This data set is matched to NOAA’s tsunami platform. It can predict tsunami passage along the affected coastlines and take the necessary actions and warnings on the spot. Communication is also an essential aspect of this method, i.e. that the immediate warning should provide credible and easily accessible information on the extent of the expected hazard. A tangible element of tsunami protection can be the construction of protective barriers. However, it is debatable whether a protective wall should be built or, if possible, whether it would be better to support the relocation of residents. Some argue that it would be ineffective to build barriers because it is difficult to calculate the maximum height of the flood (even if one does not have to prepare for a maximum tsunami height of 500 m). The floodwater often bypasses the barrier and threatens the land behind it. This type of protection was first used after the tsunami disaster in Japan in 1896. If a protective wall must be built for protection during the preparation phase, the question is what length it should be and how high it should be (Photo 2.6). Tsunami hazard is often considered in land-use planning. Using zonal logic in land-use planning, woody vegetation is proposed to cover coastal areas, thus increasing surface roughness and wave energy absorption. For a similar purpose, denser vegetation cover can be planned in the hinterland areas away from the coast towards the mainland. A tsunami can also cover these inland areas, so increasing the intensity of the surface cover seems less effective, and the falling trees in the form of floating debris can only increase the destructive effect of a tsunami reaching the land.

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Photo 2.6 Section of the 25-km-long protective walls built after the 2011 tsunami struck Fukushima (photo: Fukushima)

2.4 Natural Hazards Caused by Landslides, Mass Movements A slope is one of the basic landforms most often treated as a stable structure. However, this chapter exhibits that sloping surfaces are also subject to dynamic change, affecting the surface (e.g. soil erosion) and the deeper layers. These dynamic processes are mainly associated with steep, strongly inclined free surfaces or the convex upper sections of slopes (Keller & DeVecchio, 2016). Here, the material forming the slope is being redeposited, with different types of dynamic mass movements, and its energy is provided by gravity. While mass movements do not account for the worst losses, CRED data show that between 1998 and 2017, they caused 18,414 casualties, affected around 5 million people and caused billions of dollars in damage (CRED, 2018b). The term landslide is often used to describe the hazards caused by mass movement on a slope, sometimes involving a large aggregate (in many works of literature, the term has a narrower meaning). The term “landslide” is not good for this purpose because, whether its cause is considered from a geological or geomorphological point of view, the “landslide” itself is only one type of slope movement. These processes occur in various environments, from steep to gently sloping hillsides and often below the water surface (e.g. on the ocean floor). The primary drivers of mass movements are gravitational force and the weight of the moving sediment, but other factors also influence slope stability. In many cases, these movements can be triggered by well-defined causes (e.g. rainfall, earthquake, anthropogenic effects), which generally either increase the weight of the slope or increase its steepness.

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2.4.1 Some Types of Landslides Mass movements are defined as processes triggered by gravity directly (and indirectly by wind, water, etc.) and cause rock, debris or soil to move down a slope. If we consider a sloping surface and the effect of precipitation running down it, then logically, linear and sheet erosion that erodes the material of the slope would also fall into this category. However, soil erosion caused by water and wind typically affects the upper layers of the soil, generally acting as a slow process (see Sect. 4.5 for a detailed analysis). The case of the frozen subsoil is a little more complex. Processes belonging to the group of mass movements involve the downslope movement of entire sediment layers and blocks. Depending on the type of movement, they are usually episodic (e.g. rockfalls or landslides in mountainous areas), less frequently periodic (e.g. toppling); and sometimes occur at higher velocities (e.g. avalanches) than soil erosion, which is sometimes almost continuous and slower depending on rainfall. A specific feature of slope processes is that, overall, soil erosion removes much more material than other types (e.g. falls, slides), but the large mass of material moved at once can cause significant damage that is difficult to manage. Within mass movements, landslides are the easiest forms to identify: a rupture surface (e.g. a layer of clay or gravel) on which the upper layer of material is moving. Slope processes can be divided into three broad categories according to whether the moving mass behaves solid, rigid or plastic. Rockfalls and topples develop on steep slopes and involve free-fall-like movement of loosened rock fragments, and they often have serious consequences (Table 2.6). The process also occurs periodically on the steep river and coastal slopes where lateral erosion has steeply undermined the banks and the coastline. About four-fifths of all slope mass movement events involve some type of landslide (Glade et al., 2006; USGS4). The initiation of movement requires Table 2.6 Main types and characteristics of different slope mass movements Type

Cause of movement

Duration and speed of occurrence

Material involved in the movement

FALLS: rockfall, toppling, avalanche

Earthquake, gravitational force along shear zones

From periodic to episodic, velocity: 10–100 km/h

Boulders and blocks

SLIDES: landslide

Activation of rupture Episodic, often surface, gravitational periodic, mainly force, suitable lithology seasonal, velocity: 1–100 cm/day

Colluvium, blocks, a mixture of different layers

FLOWS: mudflow, soil flow

Oversaturation, persistent rain, gravitational force

Mainly seasonal, Slope sediments, soil, velocity: 1–100 cm/s precipitation

SLOPE DEFORMATION: soil creep

Gravitational force

Seasonal, velocity: mm–cm to year

Source Own compilation from opengeology

Mixed slope sediments

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rupture (sliding) surface created by shear stress or rupture (due to a decrease in the shear strength of the slope material, an increase in the shear stress of the material or a combination of the two), but the characteristics of the movement (e.g. depth, extent, velocity) are controlled by the slope steepness and gravitational force, in addition to lithological and hydrological factors. Several classifications of landslides are known, but the most used are those based on topographic features. Among others, rotational slides occur on an arched rupture surface, while the translational landslides have distinctive planar surfaces of weakness such as a fault, joint or bedding plane. It often forms at the boundary between loose sedimentary layers (e.g. loess), which often dries out and moves along an underlying rapture surface, such as a saturated clayey sliding surface (Fig. 2.21; Gebhardt et al., 2017; USGS4). In the middle of the Carpathian Basin, where the Danube runs from north to south, the western bank’s 50–60 m thick loess poses a serious landslide hazard (translational slide) (Mez˝osi, 2012). Table 2.6 provides a much more detailed classification than the morphological types, but the most common method is to categorise the forms into three or four groups, as it is indicated in the table. The formation of the processes indicated for the types is discussed in the following section. In addition to the fact that gravity is the basic driving force in all cases, the types are influenced by several factors from lithology to morphology. A characteristic of rockfalls is that they are almost free-falling, but apart from the less frequent large falls, they generally cause minor damage. The most common and thus the most dangerous type of mass movement is the landslide on a mountainous area where the destruction is mainly caused by a large amount of material aggraded at the bottom of the slope. The slowest process is the (soil) creep, mainly characteristic of frozen areas and common in the Pleistocene. Flows of mainly mud and soil are connected to the increasing number of flash floods in recent decades. Although rock and mudflows in dry and wet environments are classified into different categories for classification purposes, their complexity means that there is no significant physical difference between them (Hyndman & Hyndman, 2017; Keller & DeVecchio, 2016). The typology of slope mass movements is complicated because that avalanche can be included in this classification. In their mechanism, they can be related to landslides and falls, and the term is used not only in connection with snow and ice, but also

Fig. 2.21 Rotational slide (a) and translational slide (b). a 1: Rupture surface; 2: bedrock; 3: debris slump; b 1: water-permeable layer; 2: sliding plane; 3: clay; 4: debris slide (Pécsi, 1991)

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with mud and rocks (USGS2). The name avalanche itself comes from the Latin word labina (meaning landslide). It is most associated with snow because people are using high mountain areas more and more intensively (e.g. for transport, sports). Depending on the condition and stability of the snow, the snow mass can move accordingly. If, for example, a lot of snow mixes with a lot of air, it will start downhill as powder snow and can reach speeds of up to 300 km/h. In any case, there must be a sliding layer, a shear surface, along which the movement can start. Typically, a slope of 30–40° is required to trigger the movement (as slopes are generally stable up to 30°). A lot of snow, more than 30–40 cm thick, the resulting tensile and compressive tensions, strong winds or extreme cold can cause the snow mass to become unstable and start moving. Even though avalanche risk started to be analysed in detail only in the last hundred years (it was not previously considered a hazard because of the smaller mountain population), avalanches with devastating effects and sometimes high numbers of victims were recorded in historical times too. Examples include Hannibal’s campaign against Rome (218 BC), during which an avalanche in the Alps killed some 18,000 Punic soldiers, or the avalanches in the Alps (Kitzbühel) caused by artillery fire during the Second World War, which claimed tens of thousands of victims. Today, despite the very serious construction and operation of warning systems, in the Alps alone, 20–50 people are killed by avalanches every year, the most serious being the 2017 accident in Farindola (Italy), in which 29 people died (avalanche).

2.4.2 Physical Background of Mass Movements The physical background of the movement on a slope is described by the relationship between the moving weight on the slope and the force of gravity (Fig. 2.22; De Blasio, Fig. 2.22 Forces involved in slope movements (explained in the text, after Muttnyánszky, 1981)

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Fig. 2.23 Principle of shearing—explanation in the text (after Muttnyánszky, 1981)

2011; Sidle & Ochiai, 2006). Movement is essentially a displacement of material that occurs due to the shear forces that drive movement and the resisting forces that hinder it. In the case of no friction, the weight of the body (G) can be divided into two components: the forces F 1 , parallel to the slope/shear plane, and the forces F 2 , perpendicular to it. These can then be calculated as follows: F 2 = G cos α and F 1 = G sin α (α—the angle of the slope). In the case of friction, the mass G, which in this case could be a block of soil or rock, is at rest, and in equilibrium, the forces F 1 (driving) resulting from the motion and T (impeding) resulting from the friction can be equal, and their relationship can determine the extent of the motion (Glade et al., 2006). However, motion can occur due to gravitational effects and for structural reasons. The most frequent of these is shear, where the sheer force causes the sediment strata to slide over each other. The basic equation for shear is τ = V /A, where the resulting shear stress (τ ) is the product of the shear force V and the cross section A. In anybody under load, where stress is induced at its points, it is possible to find planes where shear stress (F) occurs (Fig. 2.23).

2.4.3 Causes of Mass Movements Mass movements on slopes are triggered by the change of the slope equilibrium from stable to unstable. The stable equilibrium of slopes can be altered by a few natural and anthropogenic effects, such as the incision of a stream or artificial road into the slope, which increases the angle and height of the slope, the inundation of the area with water, which increases the weight of the slope, or the removal of vegetation from the surface, which reduces the stability of the strata. The previous section discussed that the forces acting on the slope are determined by the angle and the weight on the slope. An increase in either the slope weight or the slope steepness means an increase in shear stress, which in turn can weaken stability (Hyndman & Hyndman, 2017). Both natural and anthropogenic factors can increase the steepness of the slope. Natural causes include, for example, soil erosion, the incision of a watercourse, the collapse of underground passages or volcanic eruptions, while the most common anthropogenic causes are mining, or construction works on a slope.

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Earthquakes often cause the destabilisation of the slope and the initial start of movement with an amplitude greater than 4 M. In addition, the energy released during volcanic activity can also trigger mass movements. Loose sediments (e.g. ash) formed and deposited during volcanic activity can also initiate dangerous debris flows when heavy rainfall occurs. But persistent or heavy rainfall can also be a significant trigger for mass movement; the first technical question in the analysis of landslides is often the assessment of surface and subsurface water activity. The saturation of the subsoil with moisture can increase naturally and thus significantly increase the risk of many mass movements. For example, landslides develop when rainwater or meltwater infiltrates into deeper layers or when large amounts of water flow below the surface due to artificial causes such as a burst water pipe. Some of the slides caused by rainfall can evolve into a shallow, fast-moving debris flow or silt flow containing water and sediment, the extent of which is influenced by other factors such as the inclination of the slope. Infiltration can increase pore water pressure (e.g. aquifer recharge during wet seasons or rainwater infiltration) and hydrostatic pressure in cracks and fractures, contributing to slope processes. For mass movements, not only the orographic characteristics of the slope, which in addition to the height and angle of the slope are also included in the relief of the terrain, but also the sedimentary structure of the slope and its characteristics are important. The mineral composition of the layers forming the slope, the cementation of the grains, the solidity of the layers, the degree of permeability or the presence of layers that may represent poor stability of the sediment block by conducting water or possibly creating a sliding surface may be important factors influencing slope mass movements. In general, vegetation in the functioning of geoprocesses is determined by the combined effects of orography, soil and climate. Still, the role of vegetation is important for slope stability for several other reasons too. For example, plants moderate the impact of intense rainfall, provide more opportunities for the infiltration and evaporation of precipitation, thus reducing the magnitude of runoff that causes erosion. They increase the cohesion of the slope material, thus stabilising the slope against slope mass movements. The release of slope mass movements can be exacerbated by anthropogenic activities such as deforestation, surface construction and urbanisation in general, mining, and earthworks that alter the shape and stability of the slope. Mass movements appear to be associated with many processes, from earthquakes to heavy rainfall, which can partly trigger these processes and partly have a devastating effect on themselves. These causes are generally independent of each other and, unlike other natural hazards, do not usually form a chain in which one hazard prepares the way for another. There are, however, cases where mass movement triggers another hazard. It is the case, for example, when a landslide blocks a valley and results in a flooding of the river, or when it affects a mountain reservoir and the water topping over the dam destroys the settlements in the floodplains in a flash flood. This event happened in 1963 at the Vajont Dam (Italy) in a narrow but deep valley, when material sliding into the reservoir caused the water in the reservoir to overtop the dam, destroying the village of Longarone in the Italian Alps (Telbisz, 2010). In addition to minor earthquakes, the cause may have been the significant artificial retaining

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of water that helped form the sliding surface and the resulting loss of valley-side support with increased pore pressure and weight. In general, it can be concluded that the combined effect of intense rainfall, extreme orographic slope conditions and shear-prone sediments can significantly increase the risk of mass movement.

2.4.4 Spatial Occurrence of Mass Movements On a global scale, mass movements occur most frequently in mountainous areas with large differences in topography, e.g. in the Andes in South America and the Himalayas in Asia. This sensitivity is also illustrated by a map of the mortality risk of mass movements, based on values from 1981 to 2000 (Fig. 2.24); projected onto a grid, it estimates the environmental risk posed by slope mass movements based on mortality data from previous years. The largest known mass movement formed on the edge of Norway’s continental shelf about 8200 years ago. This submarine mass movement is the so-called Storegga Slide, which displaced about 3500 km3 of material, resulting in a very large tsunami with a height of 10–20 m. The most serious consequence of the event was the destruction of the then inhabited Doggerland, a land bridge connecting Britain, Denmark and the Netherlands in the southern part of the North Sea (Fig. 2.25). The largest submarine landslide is the Agulhas movement in South Africa, estimated to be about 20,000 km3 , which occurred about 2.5 million years ago.

Fig. 2.24 Spatial mortality risk of mass movements associated with high mountains is well illustrated on a global scale. Source Dilley et al. (2005) and EMDAT (2019)

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Fig. 2.25 Area affected by the Storegga submarine slide. The blue dots show the location of tsunami deposits or other evidence on the tsunami, the numbers indicate the former elevation of the deposits above sea level, and the red dots indicate the analysed sites of tsunami deposits (after Bondevik et al., 2003)

2.4.5 Consequences of Mass Movements The number of hazards caused by mass movements between 1998 and 2017 is about the same as the number caused by extreme temperatures and droughts (CRED, 2018b). On a global scale, the number of people at risk is modest compared to other risks, amounting to around 5 million. However, this is not accurately recorded because landslides and other mass movements are included in separate categories. At the same time, the number of victims of silt flows and mudflows combined with flash floods is mostly associated with flood events. The direct and indirect impacts of mass movements are most often measured considering the consequences on living and non-living environments. Among the elements of the living environment, the number of casualties indicates the severity of the hazard, which is uncertain due to the often-problematic classification of events, often due to their complexity (Table 2.7). For example, the 1999 landslides and mudslides that devastated Vargas (Venezuela) had more casualties than the twentyyear cumulative data of CRED (2018b). Still, it was difficult to separate mudslides and flash floods in this case because of their frequent combined occurrence.

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Table 2.7 Fatal mass movements of the last century Date

Number of victims (people)

Location of the event

Mass movement type

19.05.1919 ~5100

Kelud (Indonesia)

Lahar (hot volcanic debris saturated with water) over a distance of 185 km

16.12.1920 ~200,000

Gansu province (China)

Multiple landslides after an 8.6 M earthquake

10.01.1962 ~4000–5000 Ranrahirca (Peru)

An avalanche of ice and rock triggered by an earthquake that affected eight municipalities

03.10.1963 ~2500

Longarone (Italy)

A landslide collapsed into the reservoir behind the Vijont Dam, and the overtopping water destroyed the settlement in the Piave Valley by a massive and fast flood (Telbisz, 2010)

31.05.1970 ~22,000

Yungay (Peru)

The Ancash earthquake in Peru caused an avalanche of debris and rocks with a speed of more than 500 km/h, killing most of the inhabitants of the settlement

13.11.1985 ~23,000

Armero (Colombia)

Lahar, the eruption of the Nevado del Ruiz volcano produced a hot pyroclastic flow that melted mountain glaciers and created a lahar. Debris flows and mudflows killed most of the inhabitants of the town of Amreo

14.12.1999 ~30,000

Vargas Landslides caused by heavy rainfall, debris and silt (Venezuela) flow several metres high (Vargas)

Source Hövelmann (1997) and USGS3

Most of the mass movements recorded in the last decade were mud and silt flows combined with flash floods. The mass movements that claimed almost a thousand lives in Brazil (Rio de Janeiro) in 2011 and more than a hundred in Pune, India, in 2014 were partly caused by heavy rainfall and partly by intensive deforestation. In the USA, the 2014 landslide in Oso, Washington, killed 43 people and buried numerous houses. Rainy weather is thought to have been the cause, but experts could not predict the formation of a sliding surface on gravel and clay (Photo 2.7). Similarly, the 2016 mud avalanche and mudflow in Java (Indonesia), which killed 31 people, was caused by heavy rainfall, as was the 2017 mudflow and landslides on the valley edges in Colombia, which destroyed the town of Mocoa and killed around 330 people. The landslides and mudflows in Sierra Leone in 2017, with around 400 fatalities, highlight the prominent role of anthropogenic impacts: dense, poorly regulated development, unorganised settlement patterns, poor infrastructure and significant deforestation of peripheral areas all reduced the stability of the slopes, and the average rainfall of 3000 mm together with the pronounced topography only increased the likelihood of the occurrence of mass movements on the vulnerable slopes. According to the most recent data, in 2020, landslides and mudflows caused by rainfall on the island

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Photo 2.7 Abbotsford landslide 10.08.1979—Dunedin City (NZ). Source creativecommon

of Kyushu (Japan) caused dozens of deaths and billions of dollars in damage (June 2020). The growing population of the Earth is increasingly at risk of mass movements, as society occupies more and more areas previously declared to be hazardous from this point of view. For social and economic reasons, some groups of the population are forced to occupy unfavourable slopes or unsuitable for building and, by settling there, expose themselves to increased risks of landslides. In general, mass movements affect small areas, but they can impact the natural environment, changing its morphological and ecological character. Research has shown that mass movements can damage forests and grasslands, as well as wildlife habitats and that habitats are easily destroyed through the anthropogenic mediation of the processes that trigger them. Since the direct effects of landslides do not affect a large area, flora and fauna in the affected area can regenerate relatively easily, as they can repopulate from surrounding areas. In the longer term, mass movements can also sometimes have a positive ecological impact on or improve the status of certain fish and wildlife habitats (USGS). The most common consequences for the non-living environment are damages to the built infrastructure, typically industrial, commercial and residential buildings. The problem with this is that the downward movements can last for a long time and that it is sometimes difficult to determine the end of the process, as subsequent minor movements are common. Because of this particularity, the recovery of the damage may also take considerable time. Many of the consequences of landslides can affect the transport and communication network, as damage to roads and railways often impedes the functioning of the wider region.

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2.4.6 Hazard Mitigation and Some Issues of Protection The management of mass movements, like that of other natural hazards, is about reducing the impact of the process. These can be achieved in a well-defined system. The causes, velocity and potentially destructive effects of different mass movement processes can vary widely, so, understandably, there is no universally accepted system for their management. Several tasks need to be carried out in advance to reduce and possibly prevent impacts, such as recording status, mapping areas affected by mass movements, setting up a monitoring system in movement areas and operating forecasting and warning systems. Based on this information, protection measures can be taken according to the different types of movement hazards. The establishment and operation of communication are an essential task, which is also important in the preliminary phase, not only for (early) warning systems.

2.4.7 Initial State, Monitoring and Mapping of the Process General knowledge of the state of the factors involved in the process is required before the event causing the landslide hazard, including the characteristics of the topography, the rocks constituting the surface, their sensitivity to mass movements, the stability of the system and the combination of factors contributing to the movement (e.g. sensitive sediment, dangerous inclination, exposed surface, the volume of potentially mobile material; USGS). These data can serve as a basis for mitigation decisions, helping to identify potentially high-risk locations for mass movements. One way to do this is to operate a monitoring system. There are, of course, simple signs that can be observed in the field that may indicate surface movement. Examples include particularly wet ground, cracks in the ground, changes in slope inclination (measured by the displacement of fixed rods), undulating surface, changes in fence lines, tilting of telephone poles, fences and supporting walls. For the observation and monitoring of movements, the data of which also serve as a basis for movement prediction, digital tools are now widely used rather than field observations. These sensors can be connected to previously known sliding surfaces, which can become active again. Measurements of precipitation, soil moisture and groundwater pressure and sliding acceleration can provide essential data for this purpose. In addition to the various field sensors that collect data, satellite radar and optical remote sensing instruments are available to measure surface deformation to an accuracy of a centimetre (Casagli et al., 2016). The extensive use of devices allows near real-time detection and data transmission. However, the data in the earlier Table 1.3 show that this speed does not always help because mass movements have very different rhythms (Landslide Hazards). There are very limited ways to prevent or avoid mass movements; however, their impact can be reduced. This desirable objective is achieved by collecting historical hazards in a database as part of the preparations. This database has been built up

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over many years in most countries and often includes historical data (Raška et al., 2014). In most countries concerned, databases of past landslides are available at the geological services in many places, and maps of mass movement hazard areas of varying vulnerability to movements are also available (Fig. 2.26). Traditionally, mass movement hazards have been recorded based on experience and data from previous movements, supplemented by factors such as slope angle, surface and subsurface hydrology or the characteristics of the rocks forming the slope (e.g. permeability). Based on these factors, slopes can be divided into sections according to hazard categories covering periods of decades (Chacón et al., 2006). Without an accurate assessment and measurement of mass movement hazards, no credible protection can be provided. Knowing the locations of the most frequent landslide hazards does not necessarily indicate the greatest mass movement risk; it is more helpful to identify potentially hazardous locations. On a European scale, two basic models are commonly used for areas at risk of mass movement (Jaedicke et al., 2014). One is an expert-based empirical model, and the other is a statistical model. Both are based on applying a combination of key environmental factors (e.g. slope, lithology, soil moisture, vegetation cover) and triggers (e.g. extreme precipitation, seismic activity). At the European scale,

Fig. 2.26 Probability of mass movement hazard occurrence in the USA, projected on an ArcGIS basis. Source USGS8

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Fig. 2.27 Due to precipitation and seismic triggers, the ICG and JRC models show that landslide hazards are particularly prevalent in the Mediterranean region (after Jaedicke et al., 2014)

the Mediterranean region is the most affected territory in precipitation and seismic triggers (Fig. 2.27).

2.4.8 Mass Movement Prediction Predicting the start of mass movements is not an automatic safeguard against this hazard. Especially because these processes have very different velocities, in some cases, early warning is not feasible because of the rapid onset of movement, and only the outcome can be recorded. More than two-thirds of mass movements are various types of slips, where forecasting provides more or less preparation time for partial protection of values. Early warning systems for mass movements can be produced based on data and tools collected by field monitoring and remote sensing devices. Different models have been developed to incorporate the movement triggers. For example, continuous rainfall measurements, soil water content and water pressure predict rainfall-induced movements (Baum & Godt, 2010). This forecast is based on the cumulative rainfall threshold (available for most of the USA, but also calculated from monitoring data in

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other areas) and exceedance data of intensive rainfall duration threshold, combined with soil moisture status (USGS4). Early warnings contain specific information on the areas affected by the hazard and the likelihood of occurrence. These warnings are particularly important, for example, in the case of snow avalanches in areas used for skiing or transport. In the Alpine countries and North America, services with considerable capacity help prevent avalanche risk. Complex warning systems can detect an avalanche within a short time and can immediately and automatically block off areas at risk (e.g. blocking roads and railway lines with barriers). Avalanche prediction has five to six levels, depending on the expected severity of the event. In Switzerland, for example, in the most severe extreme situation (category 6), several avalanches of up to 10,000 m3 are expected, which threatening roads and settlements in the valleys (see avalanchedanger).

2.4.9 Some Elements of Protection Against the Effects of Mass Movements A wide range of mass movements is known, so a general protection rule for specific types can only be given broadly. For example, in general, construction should be avoided in sloping areas if possible, and the slopes should be used so that their stability is not reduced. It is usually important to drain groundwater and manage soil moisture to prevent the formation of a rupture surface in the slope. Different well-developed protection techniques are known for different types of mass movements (USGS5). Accordingly, the protection procedures can be grouped based on slope movements. For example, rockfalls can be controlled by covering the slope with nets or rock anchors, anchoring the blocks with cables, or controlled blasting. The classic protection method against landslides is to build retaining walls or displace sediment prone to movement, reducing the weight on the slope. In the case of soil and mudflows, a typical defence is to divert their trail. The stability of slopes and debris retention are often achieved by increasing vegetation cover. Other approaches of protection distinguish between geometrical, hydrological and technical solutions. Geometric protection, for example, involves modifying the profile of the slope by moving the bottom of the slope further away, thus reducing the slope angle at the bottom of the slope by displacing material or by terracing, but also by reducing the weight of the material by displacement. The placement of infill (support) material at the base of the slope can also reduce the slope angle or act as a support. Hydrological protection includes activities related to water control and drainage. Draining water and reducing infiltration are effective tools because they increase the stability of the layers and reduce the weight of the sliding mass. Technical solutions include devices that connect rock blocks, such as pins, anchors or bolts, to stabilise rock surfaces.

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2.4.10 Communicating the Hazards Associated with Mass Movements When communicating the hazards associated with mass movements, it is advisable to use general risk procedures to prepare for the hazard. These questions should include providing information and recommendations to those affected on a professional basis for health, economic or social purposes. These actions can help make decisions for protection purposes, and the competent authorities can issue warnings or alerts. They may take the form of written, verbal or visual statements on the extent of the risk, its temporal and spatial extent and the wording of which should be appropriate to the severity of the hazard. The information should clarify the estimated extent of the hazard, its spatial extent, the likelihood of occurrence and the potential impact on infrastructure (e.g. networks, buildings) in the case of surface destabilising events. This information is traditionally used to update the potential hazard based on static hazard map estimates and monitoring data (EGUGA, 2017). Accessibility of the affected area is also an important criterion for disaster response and prevention.

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by using radar and optical remote sensing: Examples from the EC-FP7 project SAFER. Remote Sensing Applications: Society and Environment, 4, 92–108. Cashman, K. V., Sparks, R. S. J., & Blundy, J. D. (2017). Vertically extensive and unstable magmatic systems: A unified view of igneous processes. Science, 355, 1–40. Chacón, J., Irigaray, C., Fernández, T., & El Hamdouni, R. (2006). Engineering geology maps: Landslides and geographical information systems. Bulletin of Engineering Geology and the Environment, 65, 341–411. https://doi.org/10.1007/s10064-006-0064-z De Blasio, F. V. (2011). Introduction to the physics of landslides. Springer Dordrecht Heidelberg London New York. ISBN 978-94-007-1121-1. https://doi.org/10.1007/978-94-007-1122-8 Dilley, M., Chen, R. S., Deichmann, U., Lerner-Lam, A. L., Arnold, M., et al. (2005). Natural disaster hotspots. A global risk analysis (p. 148). The International Bank for Reconstruction and Development, The World Bank, Columbia University. http://documents1.worldbank.org/curated/ en/621711468175150317/pdf/344230PAPER0Na101official0use0only1.pdf Earle, S. (2019). Physical geology. Thompson University. https://opentextbc.ca/geology/chapter/ 11-4-the-impacts-of-earthquakes/ Gebhardt, H., Glaser, R., Radtke, U., & Reuber, P. (Eds.). (2017). Geographie. Springer Spektrum. Glade, T., Anderson, M. G., & Crozier, M. J. (Eds.). (2006). Landslide hazard and risk (p. 824). Wiley. Harangi, S. (2011). Vulkánok. A Kárpát-Pannon térség t˝uzhányói (p. 440). Geolitera (Hungarian). Herman, M. W., Hayes, G. P., Smoczyk, G. M., Turner, R., Turner, B., Jenkins, J., Davies, S., Parker, A., Sinclair, A., Benz, H. M., & Furlong, K. P. (2015). Seismicity of the Earth 1900–2013, Mediterranean Sea and vicinity (US Geological Survey open-file report 2010–1083-Q, scale 1:10,000,000). https://doi.org/10.3133/ofr20101083Q Horwell, C. J., & Baxter, P. J. (2006). The respiratory health hazards of volcanic ash: A review for volcanic risk mitigation. Bulletin of Volcanology, 69, 1–24. Hövelmann, K. (1997). Das Buch der 1000 Katastrophen (Vol. 34, pp. 135–143). Loewe Verlag. ISBN 3-7855-3123-0. Hyndman, D., & Hyndman, D. (2017). Natural hazards and disasters (p. 560). Cengage Learning. Jaedicke, C., Van Den Eeckhaut, M., Nadim, F., Hervás, J., Kalsnes, B., Vangelsten, B. V., Smith, J. T., Tofani, V., Ciurean, R., Winter, M. G., & Sverdrup-Thygeson, K. (2014). Identification of landslide hazard and risk ‘hotspots’ in Europe. Bulletin of Engineering Geology and the Environment, 73, 325–339. https://doi.org/10.1007/s10064-013-0541-0. https://flore.unifi.it/ret rieve/handle/2158/899720/29621/Jaedicke%20et%20al%20BEGE%202014.pdf Katsetsiadou, K. N., Andreadakis, E., & Lekkas, E. (2016). Tsunami intensity mapping: Applying the integrated Tsunami Intensity Scale (ITIS2012) on Ishinomaki Bay Coast after the megatsunami of Tohoku, March 11, 2011. Research in Geophysics, 5(1). Special issue on Mega Earthquakes and Tsunamis. https://doi.org/10.4081/rg.2016.5857 Keller, E., & DeVecchio, D. (2016). Natural hazards (p. 554). Routledge. Lekkas, E. L., Andreadakis, E., Kostaki, I., & Kapourani, E. (2013). A proposal for a new integrated Tsunami Intensity Scale (ITIS-2012). Bulletin of the Seismological Society of America, 103(2B), 1493–1502. https://doi.org/10.1785/0120120099 Lockwood, J. P., & Hazlett, R. W. (2010). Volcanoes: Global perspectives (p. 552). Wiley-Blackwell. Loughlin, S., Sparks, S., Brown, S., Jenkins, S., & Vye-Brown, C. (Eds.). (2015). Global volcanic hazards and risk. Cambridge University Press. https://doi.org/10.1017/CBO978 1316276273. https://www.cambridge.org/core/books/global-volcanic-hazards-and-risk/7653B9 CA75E2F32A81CE5B7110BEF8AB Mez˝osi, G. (2012). Environmental capabilities, hazards and conflicts in Hungary (p. 214). University of Szeged. ISBN 978-615-5106-01-9. Miura, O., Kanaya, G., Nakai, S., Itoh, H., Chiba, S., Makino, W., Nishimura, T., Kojima, S., & Urabe, J. (2017). Ecological and genetic impact of the 2011 Tohoku Earthquake Tsunami on intertidal mud snails. Scientific Reports, 7, 44375. https://doi.org/10.1038/srep44375

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Wallemacq, P., UNISDR, & CRED. (2018). Economic losses, poverty and disasters 1998– 2017. https://doi.org/10.13140/RG.2.2.35610.08643. https://www.researchgate.net/publication/ 331642958_Economic_Losses_Poverty_and_Disasters_1998-2017 Wang, K., Chen, Q.-F., Sun, S., & Wang, A. (2006). Predicting the 1975 Haicheng earthquake. Bulletin of the Seismological Society of America, 96(3), 757–795. https://doi.org/10.1785/012 0050191 Wicander, R., & Monroe, J. S. (2009). The changing earth: Exploring geology and evolution. Brooks/Cole. Wisner, B., Gaillard, J. C., & Kelman, I. (Eds.). (2012). Handbook of hazards and disaster risk reduction (p. 880). Routledge. ISBN 10 0415523257. Yalçiner, A. C., Pelinovsky, E. N., Okal, E., & Synolakis, C. E. (2003). Submarine landslides and tsunamis (p. 328). Kluwer. Zhang, Y., Goebel, T., Peng, Z., Williams, C. A., Yoder, M., & Rundle, J. B. (Eds.). (2018). Earthquakes and multi-hazards around the Pacific Rim (Vol. I, p. 262). Springer. https://doi.org/10. 1007/978-3-319-71565-0

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Chapter 3

Meteorological Hazards

Abstract The consequences of meteorological hazards include an increase in the number of heatwaves, extreme storms, climate extremes in general and changes in hydrological processes. The chapter summarises many types of meteorological hazards and their negative consequences. These increasing numbers of hazards are grouped into three categories: extreme temperature events (e.g. cold and heatwaves), intense wind events (tropical and temperate cyclones) and extreme events associated with convective atmospheric motions (e.g. thunderstorms, extreme winds, dust and sandstorms). Climate change is undoubtedly a key driver of these often-extreme processes. One of its most characteristic features is the increase in temperature and the transformation of precipitation patterns. Still, the measurable consequences of heat and cold waves, changing wind and precipitation patterns can also cause serious environmental, health and financial problems.

3.1 Extreme Meteorological Events A group of meteorological hazards (cold and warm temperature waves) presented here is discussed in the context of climate change in several books cited in the literature. Climate change is undoubtedly one of the main drivers of this hazard, it can mobilise meteorological processes, but it also affects many other events (Burt, 2007). However, these are most likely to be the most serious environmental and health problems of the twenty-first century (Watts et al., 2017). Increasing temperatures and changes in precipitation patterns are one of the most characteristic features of climate change, but heat and cold waves, changing wind and precipitation patterns are also measurable consequences of climate change. Consequences of climate change include the emergence of heat and cold waves, fogs, extreme storms and, in general, an increase in climatic extremes and changes in hydrological processes. The emergence of heatwaves is only one aspect of climate change, including the increase in extremes.

© The Author(s), under exclusive license to Springer Nature Switzerland AG 2022 G. Mez˝osi, Natural Hazards and the Mitigation of their Impact, https://doi.org/10.1007/978-3-031-07226-0_3

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3.1.1 Heatwaves A heatwave is the occurrence of a significantly above-average daily mean temperature that persists for an extended period. It may be mistakenly thought that this natural hazard is not a major concern in terms of mortality, biosphere condition or financial damage. As a natural hazard, there is little that can be done to reduce its impact (Photo 3.1). However, these statements are not correct; one only needs to think of the 2003 heatwave in Western Europe, which lasted 18 days and claimed 15,000 lives in Paris and 70,000 across Europe (Robine et al., 2008). The heatwave in Russia lasted for 49 days in 2010, claiming 10,000 victims in Moscow and 55,000 nationwide. People consider a heatwave as an environmental nuisance rather than a health hazard. Yet, this slow process carries serious risk, with heatwaves causing more deaths than floods, tornadoes and hurricanes together (Hyndman & Hyndman, 2017). Therefore, the health impact is the primary focus of attention among the various consequences of heatwaves and justifies a people-oriented approach to the topic. Several methods are used to assess and calculate heatwaves, the most obvious of which is the length of the extreme temperature and its extent, which can be used to estimate the severity of the heatwave. These results are essential for deciding on the action to reduce the impact. Of the methods, the Australian calculation is used by others, although the most common is to use national systems (Heatwave, 2013). The key element of most of them is the extra heat produced over three days, calculated as the difference between the three-day average values and the corresponding average mean temperature for the years 1970–2000. The Australian model uses this extra heat to determine the heat stress (EHI: excess heat index), which is calculated using the following formula:

Photo 3.1 Picture was taken at the hottest point on Earth in Death Valley (USA). Here, 54.4 °C was measured in 2020, which is the highest temperature credibly recorded (photo: van Leeuwen & Tobak, 2017 – http://www.geo.u-szeged.hu/images/death_valley.jpg)

3.1 Extreme Meteorological Events

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Fig. 3.1 Heatwave EHF (grey line) and three-day average mean temperature values (blue line) based on the 2003 European events, using Paris as an example (based on Heatwave, 2013; Nairn & Fawcett, 2015)

EHI = (Ti + Ti+1 + Ti+2 )/3 − (Ti−1 + · · · + Ti−30 )/30, where T i is the daily average temperature (measured from two datasets in Australia) and EHI is the anomaly of the three-day actual temperature relative to the previous month’s data. This value is normalised and converted to a factor (EHF = excess heat factor) and is a good indicator of the intensity and duration of heat stress. Figure 3.1 shows the relationship between the EHF and the three-day average mean temperature during the major European heatwave in 2003. For each of the solutions used to analyse the data, there are threshold values, and once these are exceeded, different types of actions are initiated. Such threshold values exist in the framework of the World Meteorological Organization (see WMO) or in the framework of the EHF calculation described above (Nairn & Fawcett, 2015). There are regularly measured parameters that provide approximate information on the state of the heatwave, but these can provide data at very different scales and timescales. Figure 3.2 shows the temperature variation on a global scale of the extreme indices based on the NOAA database. The database provides a striking illustration of the trend in temperature increases over the last decades, which may increase the frequency of heatwaves. The StatWorld database had provided data on temperature change by country and region since 1734 when measurements began. The relevant EU database, or more precisely its database collection, makes data available at the level of daily extremes and provides information on the calculation method used (Fig. 3.3). The climatological background for the development of heatwaves is the anticyclonic situation. In such cases, the clockwise movement of air masses near the surface has a weak suction effect on the air mass above. Thus, a moderate downward flow prevails, which in summer ensures dry air, uninterrupted sunshine and

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Fig. 3.2 Global-scale surface temperature change in August compared to 1880, before intensive industrialisation, based on NOAA data (Global Climate Report, 2019)

Fig. 3.3 Extreme climate data in European databases (cut-out from Temperature Indices)

thus high temperatures. Due to the high daytime and night-time temperatures, the accumulated heat load cannot be released during the night. This condition can last from a few days to a few weeks, allowing heatwaves to develop. This high-pressure anticyclone, which often covers most of Europe, also prevents moisture-bearing cyclones entering the Carpathian Basin. Of course, such an anticyclonic situation can also occur in winter, meaning humidity, fog and persistent dry cold weather. During anticyclonic conditions, air pollutants, mainly related to human activities (e.g. fossil-based energy production, transport), can accumulate due to low air movement, significantly degrading air quality. 1.

Some Spatial and Temporal Characteristics of Heatwaves

Climate change, primarily rising temperatures, has a major role in the development of heatwaves and in controlling their intensity and frequency. The press often (and increasingly) reports on the victims of heatwaves, for example, the heatwave in June– July 2019, which broke the absolute maximum temperature record in France (28 June 2019) by 46 °C, and one-third of the country’s 600 measuring points recorded peak temperatures at the end of July. According to the reports, there were “only” 1500 victims then due to good preparedness (Urfi, 2019). July 2019 was the hottest month

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Fig. 3.4 Annual total number of heatwave days of 27 °C between 1901 and 2015 (based on Lakatos et al., 2015)

on Earth since records began in 1880 (WMO). Looking back, according to the press (FAZ, 23.7.2018), 2018 was a “turbo summer”. Spatially, the extent and intensity of heatwaves in most parts of Europe, Asia and Australia have increased in line with rising temperatures (IPCC, 2014). In addition, there are, of course, areas that have shown more intense and longer heatwaves (e.g. Southern Europe, West Africa). The Carpathian Basin has also typically experienced a significant increase in heatwaves over the last thirty years. Many regional scenarios predict a 20–70% increase in the country between 2021 and 2050 due to climate change (Bartholy & Pongracz, 2010; Fig. 3.4). Various impacts of climate change are analysed in a separate chapter (Chap. 7). Temperature alone does not express the fact that it carries a health risk. In other words, for instance, a daily average temperature of 30 °C means very different things, for example, at 40 or 80% humidity. Therefore, several approaches combine air temperature and humidity in the assessment. The resulting heat index (Anderson et al., 2013) is typically used in Anglo-Saxon areas (Fig. 3.5) but is sometimes constructed as a function of dew point and temperature (humidity index). 2.

Effects of Heatwaves

Natural hazards do not occur isolated, as the occurrence of one hazard can often stimulate the development of other natural hazards, but their magnitude is not easily quantifiable. For most natural hazards, protection and mitigation of unwanted impacts are complicated by a system of interlinked processes. The impact of heatwaves can be summarised as an increase in the vulnerability of the human environment, which is assessed in terms of human exposure by addressing three issues. These summarise the impacts in the context of exposure in terms of a more natural condition, and from a human perspective, in the context of vulnerability, which primarily carries social and economic parameters, as well as adaptive

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Fig. 3.5 Hazard categories based on mean temperature and humidity. Source Heat Index

capacity (Pálvölgyi, 2013; Uzzoli et al., 2019). The results of the assessments can be particularly useful for the spatial aspects of mitigation. In the Carpathian Basin and Hungary, heatwaves represent a particular and increased vulnerability in more than half of the country, mainly in the central, eastern and southeastern parts (hohullam1). Addressing the emergence and impact of heatwaves received attention after the fatal heatwave in Europe in 2003. These impacts, particularly those related to health, have to be highlighted, more so because many people consider extreme temperature events to be the most important health risk in the Carpathian Basin at present. In several countries, the excess mortality during heatwaves ranges from 11 to 35%, but the data also show that temperature extremes are a very important environmental factor affecting health. Heat-related illnesses can be attributed to varying degrees of disruption of the thermoregulatory system of the human body (Nairn et al., 2018; Páldy et al., 2018). The disease starts with the activation of the sympathetic nervous system, and a subsequent change in the direction of dehydration can lead to the formation of thrombosis. This situation particularly affects older and less resilient age groups. It is no coincidence that the results on EHF calculation are primarily medical and have been published in such journals (Langlois et al., 2013). Over the past ten years, daily mortality in Hungary has increased by an average of about 15% during heatwave days, and excess

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mortality caused by heatwaves, which repeatedly occurred between 2013 and 2017, ranged from 20 to 1740 people/year. The health impact of heatwaves can be particularly important in larger cities, where their size can also contribute to the development of a specific urban climate and the associated urban heat island (UHI) effect. In this process, temperatures can be up to 6–10 °C higher in inner areas than in peripheral zones. The UHI may differ between winter and summer conditions, but their formation is typical. Their excess thermal energy is partly because urban buildings and dark asphalt absorb heat and therefore cool down slowly at night and the heat effects from car traffic and air conditioning (Hyndman & Hyndman, 2017). The intensity of the urban heat island could rise even higher with climate change as temperatures rise and the urban population grows (54% of the population now lives in cities, but the population flow to cities is increasing). Therefore, urban environments’ health and economic impacts are even more significant (Brian, 2017). Among the economic impacts, the first to be mentioned, in addition to lifethreatening and human health impacts, is the reduction in productivity (Tobias & Diaz, 2014). According to US data, heatwaves and hot days can reduce economic productivity by a quarter (Kiersz, 2019), with the impact on wheat and maize yields in agricultural areas being particularly pronounced. In fact, temperature and moisture stress are responsible for about 80% of the reduction in yields. Depending on the climatic conditions of a particular region, of course, these crops can be very sensitive to heat and humidity conditions during the growing season. In some places, heat stress (possibly combined with drought) can lead to very severe yield losses (Mez˝osi et al., 2016). Climate change maintains and may intensify these consequences, which is why in the longer term, it is worth reconsidering land use and cultivation technology in several areas, since, for example, adjusting the temporal sequence of wheat production (bringing it forward) may also mean a smaller increase in yields. As part of the adaptation, one should consider the possible slow phasing out of certain crops (or varieties) or consider the use of varieties. For example heat and drought-tolerant wheat varieties give a more reliable yield but much lower yields. Of course, there are economic consequences that many people regard as positive, such as an increase in domestic tourism, an increase in the consumption of soft drinks or an increase in GDP due to a significant increase in electricity consumption. An undesirable consequence of heatwaves can be the occurrence of infectious diseases or illnesses with symptoms of intoxication. According to the WHO, contaminated water or food, which can accompany heatwaves more frequently, is a decreasing but unresolved problem in several regions. The hazards typically associated with heatwaves are the separately discussed prolonged periods of drought and shorter fire events and their activation periods. Three components are required for a fire to start: heat for ignition, raw material, i.e. combustible material and the presence of a medium that feeds the process, primarily oxygen, which some refer to as the “fire triangle” (Keller & DeVecchio, 2016). In the case of fires, the heatwave is not the primary element; it does not usually trigger the burning process, which is largely due to human intervention, but the trigger can also be a previously reported meteor strike or lightning. When approaching the spread

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of fire from a geo-environmental perspective, i.e. when determining which areas are at serious risk, it is customary to consider not only the temperature (here, the dryness is important) but also the vegetation and orographic conditions (which can accelerate the spread of fire). According to the types of fire, a distinction is usually made between surface fires (which affect the grass and shrub layers) and canopy fires, which cause the most severe damage. Photo 3.2a, b show the MODIS image of smoke from a fire in the central part of the Carpathian Basin in 2012. Increasing soil erosion susceptibility and critical air quality as a consequence of fires require active protection and special management for rehabilitation. Fire smoke exacerbates poor air quality due to heatwaves (it is no coincidence that car traffic is often restricted). 3.

Heatwave Mitigation, Responses to Heatwave Hazards

As previously described, in response to the significant health and environmental risks posed by heatwaves, most countries have warning systems in place, and several Photo 3.2 a Satellite image of the north-northwest spread of smoke from the 2012 forest fire in Bugac (Central Hungary). b Juniper area destroyed by the 2012 forest fire in Bugac (Central Hungary). Source Szatmári et al. (2016)

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countries have also established comprehensive early warning systems. Meteorological forecasts are available everywhere, so there is a way of predicting heatwaves that do not occur within a long-time horizon. Climate data for these are obtained from the relevant climate service providers. These forecasts can be used as a basis for analysis and action to reduce the impact of the heatwave hazard. An example is the issuing of warnings. These values are often classified as a yellow or red alert for daily average temperatures above 25–27 °C, but this varies from country to country, as does the calculation of the daily average. The health thresholds for heat stress are set at 32 and 38 °C, which is, of course, not a mean temperature value. Hungary has a three-stage heat warning system (Páldy, 2013). The first (informative)-stage criterion is that the daily mean temperature must reach or exceed 25 °C for at least one day (which implies a 15% increase in mortality). The first stage of the warning is based on a daily mean temperature of 25 °C for at least three consecutive days (or exceeding 27 °C for one day, which can imply a 30% increase in daily mortality). The next stage of the warning, a second-stage (orange) warning, is based on a daily mean temperature of 27 °C for at least three consecutive days (with a similar risk of mortality) (MET). In Hungary, the National Centre for Public Health (NNK) is responsible for informing those concerned about the extent of the warning. At the same time, the notification of the population and the preparation of the protection measures are now the responsibility of the local authorities. A key question is what can be done to reduce or mitigate the impact of a heatwave. In terms of timing, the tasks before the arrival of heatwaves are basically preparation. Here, the task could be to set up and operate a warning and alert system and ensure that it is regulated by legislation. Many countries have such systems in place and are in operation; in the aftermath of the 2003 European heatwave, France reduced the number of heatwave-related deaths by a tenth thanks to prepared prevention and information to the public. The key issue is to ensure that the right information is passed on to healthcare providers and local authorities with a legal obligation to act and the population affected (Uzzoli et al., 2019). It is advisable to assist in planning communication, contacting the local media, especially in evacuation, and preparing institutional heat plans. It is also important to document the consequences of heatwaves and the related activities in detail, as these can serve as lessons for better management of a next event (hohullam1). Reducing the impact of heatwaves is mostly a longer-term task. These tasks could include increasing (urban) forest cover, implementing thorough education and information programmes, or in the shorter term, improving air quality or providing cool places for the elderly and vulnerable (e.g. by organising volunteers to do this). Helping to empower civil society organisations or NGOs (e.g. local movements), decision-makers (e.g. strategic planners) and decision-makers (e.g. local authorities), representatives of the scientific community and national actors (e.g. in legislation) is a must.

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3.1.2 Cold Waves Cold airwaves are one of the less frequently mentioned types of natural hazards, as the analysis of their occurrence and, for the most part, their harmful effects are often neglected. Although this weather phenomenon significantly impacts humans and the economy, it is still not clearly explained by profession. More precisely, several elements related to this explanation are known and proven, but they do not form a coherent system. It is easy to understand why, in many countries, this phenomenon is therefore described in descriptive terms only. It is generally agreed that a cold airwave arrives from higher latitudes and rapidly intensifies as it enters the mid- and low-latitude regions. However, the definition is descriptive in this form: in the USA, for example, the term cold wave is used when the average daily mean temperature falls below −7 °C. Its duration and extent are categorised separately by the cold air outbreak (CAO) index (Smith & Sheridan, 2018). Using this logic, it is no coincidence that cold wave alerts in China are prepared in a breakdown, using the same logic as for heatwaves: red warnings are issued if minimum temperatures are expected to drop at least 16 °C within 24 h, and minimum temperatures are less than 0 °C; orange warnings if minimum temperatures are forecasted to drop at least 12 °C within 24 h (with similar minimum temperatures and wind conditions); yellow warnings if the drop reaches 10 °C; and blue warnings if minimum temperatures drop to at least 8 °C within 48 h and minimum temperatures are forecasted to be less than or equal to 4 °C (alertchina, 2018). One explanation for the formation of the cold wave is the presence of low-pressure cyclonic vortices over the polar regions (in the troposphere and higher in the stratosphere). In the troposphere, this low-pressure cold atmospheric formation of 1000– 1500 km is bounded at the margins by polar vortexes, called jet streams. This lowpressure polar region traps the cold, high-mass air at the poles (Fig. 3.6). The functioning of the system is essentially controlled by the air pressure differential. Due to the nature of the jet stream, it varies in a meandering fashion, allowing larger and very cold air masses to enter regions to the south, such as the USA or Europe, and in turn, allowing extra warm air masses to enter the Arctic regions. According to many, in the long term, the weakening of the polar jet stream is caused by climate change, which increases its meandering, and this may explain that while several continents are experiencing cold waves and exceptionally cold temperatures, hot temperatures in the north are setting records (NOAA, 2019). The weakening effect of the lowpressure circumpolar vortex, the jet stream (prevalent mainly in winter months, but affected by climate change), allows warm air masses to push deep north and cause extra heat, such as on Svalbard (Spitzbergen) in 2018 and 2020. Another explanation is that the persistent cold waves are caused by extraterrestrial processes, the most common of which is a lack of sunspot activity. Historical sources show that during the Maunder Minimum (1645–1715), only 16 sunspots appeared in 71 years, while none appeared during the 116 years of the Spörer Minimum (1402– 1516). These cases can indeed be paralleled and placed in the climate disruption phase of the Little Ice Age (circa 1280–1860). However, this seems less and less

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Fig. 3.6 Polar vortex and its associated air flows. Source NOAA (2019)

a suitable justification, because on the one hand, the relationship between sunspot activity and the temperature still needs to be further clarified, and, on the other hand, they represent very different timescales. Cold waves are events of a few days or a few weeks, whereas sunspot activity can impact an annual scale. The third explanation for the formation of cold waves is that very large amounts of dust and ash released into the atmosphere by volcanic eruptions prevent irradiation, which results in cooling. This effect was spectacularly illustrated, for example, by the 1816 Icelandic volcanic eruption, which caused a “year without a summer” in France and had severe agricultural consequences. This link was suggested much earlier, and one of its bases may have been the prolonged cold wave of 1709. At that time, the Baltic Sea froze over for four months, similar to the Amsterdam canals or the Ebro River, and Venice was a place to skate and not travel by gondola. In the years before that, several volcanoes erupted, such as Teide, Santorini, Vesuvius and Mount Fuji in 1707, followed by Asama and Fournaise in 1708, the atmospheric dust from which may have caused the weaker irradiation. The specific causes and the extent to which they may have caused the cold wave are still under debate. Cold waves are a regular occurrence, with high-intensity events occurring every two years. The question may be how predictable this atmospheric phenomenon is. It depends essentially on meteorological forecasting, which today provides data with reasonable reliability over 10–14 days. It can be concluded that the forecast of cold waves is better in the winter period. Still, the determination of the beginning and end of the waves using historical events is of low reliability (Lavaysse et al., 2019). The formation of cold waves may be altered by climate change as the stability of the polar currents decreases, forming larger waves and extending deeper into higher and lower latitudes.

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The impact of cold waves on human life is nowhere near as great as that seen with heatwaves. There is evidence that mortality increases at low temperatures, but little is known about the wider effects of cold waves (Ryti et al., 2016). According to data from reinsurer Munich Re, the cold wave in 2006 claimed the most victims in Europe between 1980 and 2012 (790 people). Eastern Europe and Russia were also significantly affected by this cold wave. The cold environment requires higher calorie intake and can cause health problems (e.g. fever, tracheitis, apoplexy, asthma, myocardial infarction; see also Rocklöv et al., 2014), although it is easier to adapt to than prolonged heat. Exposure to cold affects fewer people globally, as relatively fewer people live in latitudes affected by such hazards. When estimating the economic consequences of the hazard, it is worth highlighting those cold waves to a large extent increase the demand for electricity and fuel, while, at the same time, electricity generation is disrupted for most hydroelectric power plants due to the freezing of the water needed to generate hydropower. Icy weather caused by cold waves can adversely affect traffic and transport. Munich Re estimates the direct financial loss caused by the cold wave that hits the UK in 2010 at around e2 billion, compared with an estimated e1.3 billion for the December 2009 cold wave that affected northern regions of Europe from the Netherlands to Poland. In the USA, the cold wave caused serious damage in January 2014, with a value of around $2.5 billion (costofweather, 2015). Cold waves can cause severe damage to vegetation, especially in the early and most vulnerable stages of growth, resulting in significant yield losses. In comparison, there is very little evidence of a beneficial effect of cold waves on the thermal balance, which can help to maintain the ecological balance of nature. While satisfying the concept of natural hazards, the cold wave is difficult to fit into a chain that would carry the mobility of other related hazards. However, in the context of climate change, we see more evidence that cold (and heat) waves will become more frequent than at present, appearing further north and south and increasing in severity (Szalai, 2016).

3.1.3 Fog Hazard Fog is a type of precipitation of water vapour or mist in the atmosphere, and in this respect, its formation is like that of clouds, but the process takes place in the air layer above the ground. The humidity of the cooling air is converted into very fine spraylike water droplets, which are suspended in the air because of their lightweight. The real danger is the haze, which can severely reduce visibility, which is not only one of the most important features of the hazard; its definition also includes a degree of visibility below 1 km (Fog, 2019). Fog formation requires an adequate water vapour content in the air, condensation nuclei on which water molecules condense and a modest air movement. Air saturation is key to its formation because fog can form when it no longer holds moisture and condenses (köd, 2019). Essentially, it is the combination of the above factors that

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determines the different types of fog (Samson & Ahrens, 2011). Radiation haze is formed when the air cools down, as it can carry less water vapour, which then appears as fog. Such cooling can occur (especially) on cloudless nights when radiation cools the surface and the air. In the case of advection fog, the temperature can also cool below the dew point when cooler air passes over the surface. Even small differences in topography can be expected to cause cold air to flow down a slope and form a so-called slope fog at the accumulation site (Kaltluftabflussmodell, 2005). Fog can also form when there is excess moisture in the air (e.g. due to different land use and thus different heat and water contents of surfaces), and then fog can form even at lower cooling temperatures. Hazardous Effects of Fog and Their Mitigation When we examine the impact of natural hazards, we look primarily at the damage they cause to human life and health. Compared to other natural hazards, the impact of fog is modest, but together with the environmental damage it occasionally causes, it can create a critical situation. When analysing its impact, the occurrence of fog is not the real danger because it is difficult to “compete” with the annual 200 foggy days in Northeastern Canada (about 20–40 foggy days/year in Europe). Rather, it is the combination of foggy conditions with poor air quality that can cause a critical situation. In other words, it is not only the density of the fog (e.g. drastic reduction in visibility) but also the emission of pollutants (e.g. SO2 , combustion products) into the atmosphere that can cause severe effects. The combination of fog and air pollution caused serious problems in London as early as the 1200s, but a major disaster only occurred in 1952 because of fog and smoke. After Second World War, poor-quality, high-sulphur coal burning, increased car traffic and fog had a suffocating effect on transport and social events (e.g. schools and cinemas were closed). As a result of the suffocating smoke, hundreds of thousands of people suffered from mild to severe respiratory illnesses, while the death toll was estimated at between 6 and 12 thousand (Bertus-Barcza, 2006). As a result of this event, regulations were introduced to control the number of pollutants released into the air, reducing the risk of smog. A smog alert system was developed and has since been implemented in many countries. Compared to previous years, air quality has improved in England, so there are fewer smog alerts. From the point of view of health, an important question is when fog turns into smog. In the twentieth century, smog was a mixture of smoke and fog. Today, this term has been extended to include ground-level ozone and other pollutants as constituents of this mixture. (Ground-level ozone itself can cause serious health problems.) Certain organic compounds and nitrogen oxides react chemically with sunlight to form ozone. The formation of smog is related to the amount of traffic, but other pollutants from factories and power plants can also accelerate its formation. As well as adversely affecting vegetation, smog can attack the lungs when it enters the airways, causing serious respiratory diseases and neurological damage. Several settlements have monitoring systems and a database of air quality data to predict this atmospheric hazard, which can be used as a basis for protection. The smog alert is

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based on the concentration of air pollutants (e.g. nitrogen dioxide, sulphur dioxide, ozone, particulate matter) measured by these networks. An informative or alert stage is imposed if three consecutive one-hour averages of the concentrations of air pollutants measured at three stations at the same time or, in the case of particulate matter (PM10), two consecutive 24-h (calendar day) averages exceed the informative or alert thresholds set in the regulation (see ÉMI-KTVF). The issuing of a smog alert is the responsibility of local authorities in Hungary. Fog can also cause environmental problems when it appears on its own. Dense fog can be dangerous for driving, shipping and air traffic, i.e. for commuters, mainly because of a significant reduction in visibility. Fog can lead to numerous traffic accidents every year. In addition, tiny liquid water droplets in fog can freeze instantly on exposed cold surfaces if the surface temperature is below freezing point. It is a serious reason for caution because of the risk of slipping. It is also worth mentioning the phenomenon of acid fog, which fortunately is slowly being forgotten, and which has caused considerable damage to vegetation. The use of more modern techniques has reduced the concentration of SO2 and NO2 in the atmosphere, thus reducing the possibility of acid fog. When mitigating the effects of fog, existing recommendations to reduce speed, increase visibility and personal protection against smog should be considered first and foremost.

3.2 Tropical and Temperate Cyclones and Related Phenomena, Hazards The similarity between tropical and temperate cyclones is that they rotate anticlockwise in the northern hemisphere and have low-pressure values in their centres. The differences are partly due to their size, with tropical cyclones ranging from 500 to 1500 km in diameter and temperate cyclones being larger, ranging from 2000 to 3500 km. Their different formation explains the absence of climatic fronts in tropical cyclones compared to temperate cyclones. The central part of the latter, as mentioned above, is dominated by cool air due to its formation, while tropical cyclones are 10–12° warmer than their surroundings in this zone (tropicalcyclonelecture).

3.2.1 Tropical Cyclones Tropical cyclones form over the oceans between latitudes 5 and 20°. They form when the ocean surface temperature is above 26 °C, from where the warm, moist, humid air rises to high altitudes and spreads out across the tropospheric boundary. As the rising air cools, the moisture slowly precipitates, and the system releases latent heat. The Coriolis force causes the atmospheric system to rotate anticlockwise. In the centre

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Fig. 3.7 Schematic structure of a tropical cyclone, side view (arrows indicate the direction of air movement). Source tropical cyclone

of the system, as in tropical cyclones, an “eye” can form with a diameter of several dozen km, separated from the rising air by a pronounced cloud wall (Fig. 3.7). In this zone, the winds blow downwards, the air pressure is very low (870–960 hPa compared to the average of 1000 hPa), and the air temperature is 10–12 °C warmer (which is normal for this type of descending air mass). By absorbing moisture from these surrounding areas, cyclonic clouds bring heavy rainfall (Keller & DeVecchio, 2016).

3.2.2 Main Characteristics of Hurricanes and Typhoons Two typical forms of tropical cyclones are hurricanes, which form over the Atlantic Ocean, and typhoons associated with the Pacific Ocean. These have the highest wind speeds at the edge of the cloud wall. Hurricanes are classified according to their wind speed on the Saffir-Simpson hurricane wind scale (SSHWS), which is more empirical, with wind speeds below 60 km/h being classified as atmospheric depressions, below 119 km/h as tropical storms and only speeds above 120 km/h being classified as hurricanes. These are divided into five categories according to the magnitude of the maximum wind speed, which also indicates the magnitude of the potential damage (Table 3.1). Hurricanes and typhoons generally travel northwards from their point of origin over the oceans at a low (and mostly not self-sustained) speed of about 30–40 km/h and can pick up energy and moisture over warm seas so that the excess energy absorption can cause wind speeds in the cloud wall to reach up to 250 km/h, compared to calm conditions in the central part. Around half of tropical storms become hurricanes or typhoons, with around 45 and 25, respectively, each year.

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Table 3.1 Wind speed scale associated with Saffir-Simpson scale for hurricanes Category Sustained wind speed (km/h) Examples of expected damage 1

119–153

Minor damage: possible damage to roofs and gutters of well-constructed houses; the triggering of landslides on waterlogged slopes, the breaking of tree branches, damage to overhead power lines and the resulting power cuts lasting up to several days

2

154–177

Moderate damage: major roof damage to well-built houses; landslides, trees with shallow roots uprooted, blocked roads, widespread power blackouts for several days or weeks

3

178–208

Significant damage: severe damage to well-built homes and their foundations; numerous fallen trees; many blocked roads; power blackouts; and water shortages for days or weeks

4

209–251

Extensive damage: severe damage to well-built homes: loss of roof structure; most trees are falling: power lines being torn down, roads impassable, power blackouts for weeks or months

5

>252

Catastrophic damage: well-built homes destroyed (walls collapsing), trees are falling, power lines torn down, roads blocked or washed away, water pipes failing, power outages for weeks or months

Source https://www.weather.gov/mfl/saffirsimpson

1.

Geographical Location

As noted, hurricanes are typically generated in the Caribbean Atlantic, while typhoons are typically generated in the Western Pacific. There is a slight difference in the time of their occurrence, as both occur in the summer months, hurricanes often in the second half of the season, but typhoons tend to occur in the first half of the summer. Tropical cyclones, and more recently temperate cyclones, are named. In contrast, hurricanes were originally named after the saints’ days, in line with the Caribbean and Central American traditions, and then given first names. Of course, hurricanes and typhoons are not of equal intensity. Their impact made Hurricane Katrina in 2005, which reached Category 5 intensity over the Gulf of Mexico, as did Sandy in 2012 or Andrew in 1992, particularly memorable. Katrina slowed down as usual over land, lacking the warm temperatures and moisture fuelled by seawater, so it could not sustain its energy and weakened first to a Category 3 hurricane, then to a tropical storm and finally died. Of all typhoons, Haiyan (Yolanda), which hits the Philippines in 2013, was the most active with a Category 5. The typhoon threat also affects several other areas ranging from the Japanese islands to the Asian Pacific region (Hyndman & Hyndman, 2017).

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Fig. 3.8 Fatalities and financial damage caused by hurricanes in the USA (after NOAAgov)

2.

Some Environmental Impacts of Hurricanes and Typhoons

These tropical cyclones are the most severe natural hazards globally in several areas. Coastal areas are particularly vulnerable, where, in addition to high wind speeds and heavy rainfall, they can also cause significant flooding. Once they reach the coast, hurricanes or typhoons can create a storm surge of 6–8 m high, affecting coastal areas of up to a length of 80–120 km. For example, Hurricane Katrina flooded New Orleans, which was otherwise mainly below sea level, with a population of over 500,000 originally, but which fell to 200,000 due to the storm and has now grown to over 400,000 due to intensive reconstruction work. The change in the number of casualties and the value of the financial damage caused by hurricanes affecting the USA is shown in Fig. 3.8. The typhoon surge that hits Haiyan (Philippines) extended deep into the mainland, claiming a total of 6340 lives and causing more than 650,000 people to lose their homes. It also illustrates the high vulnerability of these lowlying, densely populated coastal regions to certain natural hazards. Therefore, it is understandable that 85% of deaths are caused by natural hazards, and 39% of total economic losses occurred in those regions of Asia where a large percentage of the population live. Hurricanes and typhoons can cause significant damage, mainly on islands and on the continental perimeters, i.e. in densely populated areas (hurricane, typhoon). Accordingly, in the southeastern coastal region of the USA, higher risk locations are identified by the return period of hurricanes over the last 100 years (Fig. 3.9). For the “hot spots” thus identified (e.g. Florida, Texas, Mississippi estuary), it is particularly appropriate to prepare in advance, i.e. to develop detailed plans for flood protection, evacuation or technical facilities (e.g. a shutdown plan, considering the oil platforms of the Gulf of Mexico) (Fig. 3.10). The violent winds of hurricanes and typhoons are not the only causes of damage, although their speed alone can have serious consequences. The strength of the winds determines the wave height due to storm surges, which can be as high as 8–10 m (e.g. in Bangladesh or Australia) and can flood large land areas. It is illustrated that while an average wind speed of 40–50 km/h can generate waves of 2–2.5 m, a

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Fig. 3.9 Hurricane return period based on historical NOAA data. Source nhc

Fig. 3.10 Paths of Hurricanes Katrina and Rita related to oil and gas platforms in the Gulf of Mexico. Source US Dept. of Interior

100 km/h wind can generate 9–10 m. Wind-generated storm surges can significantly and effectively transform coastal areas through erosion. However, the extent of the damage depends on several factors, such as water depth, the run of the shoreline relative to the wind direction, the material and morphology of the coast. Although natural hazards caused by tropical cyclones can cause a wide range of damage directly related to human life and properties, they can also pave the

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way for other hazards: coastal hazards (see coastal hazards; coastal erosion), floods, landslides, heavy thunderstorms. Compared to other hazards, these are less likely to occur in chains. Concerning climate change, most authors predict an increase in the intensity of tropical cyclones rather than an increase in their numbers, but further measurements are needed to establish a plausible trend (Hendricks et al., 2019). 3.

Mitigation of Impacts

Tropical cyclones cannot be stopped, so reducing their wide-ranging impacts should be the task of protection. Two logical groups of problems should be solved to do this target. Those belonging to one of them aim to prepare for the event before it happens. For example, informing the affected population, developing a protection strategy, preparing an evacuation plan, setting up infrastructure to protect against the impact (e.g. the Dutch Maeslantkering’s protection against the storm surge; see later: Fig. 7.11). The other group could include continuous data provision and an early warning system since a few days’ warning can significantly help prepare for the hazard. Several systems are available in the USA or Canada (for hurricanes: Fig. 1.9).

3.2.3 Temperate Cyclones A temperate cyclone is formed at the boundary of cold and warm climatic air masses with different densities (along the so-called polar front). The formation process starts with fluctuations in the air masses, with the warm air pushing in towards the cold (see metnet). This process leads to a pressure drop in the central part of the cyclone due to the convergence, congestion or forced upward flow of air. This convection is the source of the winds associated with temperate cyclones. In temperate cyclones, unlike tropical cyclones, there are atmospheric fronts, of which the cold front has a higher speed (40–60 km/h) than the warm front (30–40 km/h), so that when the latter is caught up, cold air fills the cyclone, and thus, the central part carries cold air. Temperate cyclones are large-scale atmospheric formations with diameters of 2000–3500 km, which can produce large amounts of intense precipitation in a short period associated with cold frontal thunderstorms, but at a magnitude lower than tropical cyclones. Temperate cyclones have an average lifetime of one week (4– 9 days), but they are typically more active in the winter half of the year, unlike tropical cyclones. A good example of this is the Cyclone Ciara (temperate cyclones are now also named), which reached Eastern North America and Western Europe in February 2020, filling the Gulf of Mexico with high moisture air and causing large temperature differences. The strong flow caused significant wind and rainfall damage. During Cyclone Ciara, wind gusts over 150 km/h were recorded in the UK (with similar values recorded in Tyrol, Austria), and rainfall in Wales was 177 mm in 24 h. The storm also caused significant storm damage in the Carpathian Basin, with strong southwesterly winds of over 100 km/h, causing the water level of Lake Balaton

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to shift, creating a flooding difference of almost one metre between the southwest and northeast basins. On a regional scale, temperate cyclones in Europe play a key role in balancing the large temperature difference between the Atlantic and the central and eastern regions of Russia during the winter half of the year. Climate change is reducing these differences in this region, which may reduce the occurrence of large windstorms. Windstorms associated with cyclones across the European continent, and the thunderstorms and downpours they generated, caused significant damage. Cyclone Kyrill in January 2007 alone caused a financial loss of e5 billion in the EU, with 46 reported injuries (Fig. 3.11). In Asia, in 2015, the damaging effects of Cyclone Pakistan caused 45 deaths and more than 200 injuries. In October 2019, Cyclone Kyarr, which affected the Eastern Arabian Peninsula, Southern Pakistan and India, moved slowly in a SE direction but with wind speeds sometimes exceeding 200 km/h, making it the most severe storm in recent years. No damage information has been released so far. Cyclones are essentially related to processes similar to convective air currents, which will be discussed in the following chapters. The result (e.g. rain, thunderstorms, windstorms) is similar, but the processes that form them are different (see AIR Worldwide, 2015; Frame et al., 2017).

Fig. 3.11 Major windstorms across Europe between 1998 and 2009. Source EEA (2010)

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3.3 Extreme Climatic Phenomena Associated with Convective (Vertically Mixing) Air Mass Movement 3.3.1 Thunderstorms A thunderstorm is an extreme atmospheric phenomenon characterised by a strong convective (upward) airflow and accompanied by strong lightning activity and is therefore also characterised by its lightning frequency (see next section). The upwelling creates storm clouds (cumulus, cumulonimbus). The speed of the upwelling is so high that the size of the raindrops falling from them can reach the theoretically possible maximum of 6–8 mm. As the droplets move up and down due to convection and repeatedly reach heights of 6–8 km and freeze due to their surroundings, they can become larger and larger, leading to the appearance of hail. The precipitation intensity can be high during downpours, but thunderstorms are not always accompanied by precipitation, sometimes only by lightning. However, thunderstorm clouds can produce up to 20–30 mm of rain in a short period, but much higher values have been recorded, with rainfall exceeding 50 mm in a short period. The logical order of thunderstorms, flash floods and erosion is associated with the process and its consequences. The data on impacts are different globally than what we have seen in ourworldindata.org/natural-disasters and emdat.be databases, analysed earlier in Sect. 1.1. However, phenomena such as lightning or tornadoes cause, on average, about the same number of deaths as floods over 30 years. They also cause huge losses, and therefore, the use of the term natural hazard is justified in their case. In case of thunderstorms, the primary hazard is lightning, as described in the next section, and thunderstorms can be accompanied by strong winds, which can cause minor damage to infrastructure and vegetation. Over the last three decades, thunderstorms have increased in intensity in both Europe and North America, which has meant an increase in losses of various kinds. Severe thunderstorms can occur in many places, but to reduce the impact of the phenomenon and reduce losses, it is recommended to identify areas where the probability of thunderstorms is higher. Most thunderstorms occur in the equatorial belt on a global scale, where one or two are recorded daily (Keller & DeVecchio, 2016; Fig. 3.12). The greatest damage associated with thunderstorms is the wind that develops in supercells. The rotating updraft in a moist, warm atmosphere and the associated low-pressure structure is also known as a mesocell. The swirling upward rotational motion can occur at high wind speeds, often resulting in a tornado (or tuba). In future, higher temperatures and a more humid atmosphere caused by climate change could lead to an increased risk of thunderstorms. This process will mean increased damage in Europe and North America, for example, because buildings

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Fig. 3.12 Annual average density of thunderstorm-related lightning strikes per km2 . Source GlobalFrequency

and other infrastructure are particularly vulnerable to damage during heavy thunderstorms. The related prevention measures should be adapted to the pattern of thunderstorm hazards.

3.3.2 Lightning Lightning is particularly common during thunderstorms, which is essentially an extraordinary short circuit connecting two points of different potential. When there is no metal-to-metal contact between them, the air is the conductor, through which the short circuit, a spanning, occurs, requiring a voltage of about 320 V. This is the fundamental cause of the formation of lightning. However, its types are affected by many other environmental factors. A very old typology is used to distinguish between linear lightning (zigzag), surface lightning (between thunderclouds and the surface) and ball lightning, which travels slowly but causes great damage by burning (Rakov & Uman, 2007; Photo 3.3). The lightning “discharge” is accompanied by very high voltages (many tens of millions of volts) and currents (10 thousand amperes), which are millions of times higher than the values normally used in everyday life. Lightning can also occur when a cumulus cloud develops into a cumulonimbus cloud. Observing and recording lightning is not very complicated, and most national meteorological services measure and map it. Lightning can now be monitored online, e.g. Fig. 3.13 shows the spatial distribution of about 40,000 lightning flashes in Europe in 48 h, with the area units classified according to the number of lightning flashes recorded at a rate of 40 flashes/minute (e.g. 0–40 flashes/pixel). Lightning can also be tracked globally online (see Blitzortung.org). The question arises why lightning mapping is useful and how much lightning falls within a natural hazard scope. On the one hand, the answer may be that

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Photo 3.3 Linear lightning (photo: vonalasvillam)

the knowledge of this event, which is always accompanied by thunderstorms, can increase predictability, preparedness and safety. In addition, this phenomenon can be dangerous for humans; for example, in the USA (2018), the number of victims was comparable to that of tornadoes, hurricanes or windstorms (Fig. 3.14). Even a millionth of the energy released during lightning is dangerous for the human body, and the health effects depend on the current intensity and transit time through the body. In the case of a lightning strike, a very short time (a fraction of a second) but a very high current must be expected, at which the muscle spasm induced can be fatal. The number of deaths caused by lightning in Great Britain is low due to the low intensity of thunderstorms: on average, there are 0.05 deaths per million inhabitants (Elsom, 2001). However, a single case can also carry great involvement (BBC, 2019a). With great uncertainty, the global estimate of deaths resulting from lightning strikes is around 2000 per year, but this figure often has unrealistic estimates (Holle, 2008). The risk of lightning increases air humidity, surface contamination and the socalled peak effect. The resistance of dry skin is about 100,000 , compared to 5000  for wet skin, i.e. the moisture on the skin reduces the resistance to one-twentieth. In the risk of being struck by lightning, it is necessary to avoid elements that give rise

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Fig. 3.13 Lightning observed in Europe between 10 and 12 December 2019. The colours show the number of flashes that occurred in the pixel area during the two days analysed. Source onlinevillam

to a “peak effect”, such as protruding sharp objects or trees in flat areas, which have a higher charge density and therefore a higher electric field strength in the vicinity.

3.3.3 Extreme Rain, Freezing Rain, Snow, Blizzards and Snowstorms Depending on other environmental elements, the type and amount of precipitation in the form of water vapour in the atmosphere is undoubtedly an important feature of a region’s climate. The precipitation formation process is triggered by the cooling of the atmosphere, which can then become saturated. The condensation of water first appears in the form of small droplets. The smallest particle diameter element of falling precipitation is low-intensity drizzle, which can merge into larger-grained but similarly liquid rain. Under extreme rainfall, the maximum daily amount is given in mm (index used in meteorology: RX), and extreme intensity is measured by the ratio of the amount of rainfall and the number of rainy days (index: SDII). Largediameter water droplets formed in a violent updraft (convection) can take the form of

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Fig. 3.14 Number of victims caused by natural hazards. Source National Weather Service

high-intensity showers (which can produce large amounts of precipitation in a short period: the island of Reunion, which recorded a peak of 1830 mm of rain in 1 h in 1952, is the world record holder for rainfall in an hour). Precipitation can also take other forms, such as ice or snow crystals. Thus, in the case of snowfall, the crystals are also solid and, depending on the temperature, can form a regular hexagonal shape. Of these types of precipitation, hail is the most likely to cause damage to agricultural areas or infrastructure. Hailstones can be larger than 5 mm in diameter. The growth of hailstones is since, in thunderstorm clouds, the water content in the very strong updrafts results in the growth of these ice particles, which fall to the ground in a solid state when they are too large to be held in suspension by buoyancy. Although it may not cause major natural damage, freezing rain can cause serious difficulties. It is formed when warm air is above the lower cold layers of air, and the rain that forms here freezes near the ground, even freezing to any exposed objects on the ground. A wide range of transitional forms are known, from snow through sleet to graupel (see National Meteorological Service—Országos Meteorológiai Szolgálat). Non-falling precipitation types (e.g. dew, frost or rime ice) appear on the surface of objects near the surface, such as plants. Our previous understanding was that rain itself was not directly considered a natural hazard. The rain does not directly cause disasters to human health, life or infrastructure. However, rainfall that provides extra volume can, like the natural hazards described above, trigger associated processes that meet the definition of a natural hazard in all respects. Such processes may include floods, flash floods or the

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Fig. 3.15 BBC news report on the rain hazard in Japan in summer 2019. Source BBC (2019b)

occurrence of landslides. These processes are discussed in separate chapters because of the effects of extra rainfall. In everyday communication, however, the extra rain is described as a natural hazard, which may have required, for example, the evacuation of thousands of people (Fig. 3.15). However, the rainfalls reported in the media were not extraordinary, as the heaviest rainfall was recorded in 1861, when 26,470 mm of rain fell in Cherrapunji, India, during the monsoon. From floods that can endanger human lives to flash floods, heavy rains can also cause serious damage to infrastructure. The significance of these effects explains why these extra rainfall events that trigger secondary processes are studied in great detail worldwide. Concerning heavy rainfall, the main questions are: how much rain falls in a given circumstance, what are the conditions under which heavy rainfall occurs and what is the nature and extent of the damage it can cause? Because of this approach, the amount and intensity of precipitation are measured primarily. Hence, a close relationship is assumed between the magnitude of the extra rainfall and the extent of the damage. The first weakness of this relationship is that it is difficult to quantify the amount of precipitation accurately spatially, and this uncertainty is difficult to measure and reduce. The measurement of rainfall is point-based, and it is problematic to derive spatial data from discrete mathematical values of precipitation (Blanchet et al., 2019). It can be done using kriging or multivariate regression, but the relationship between statistical results and the physical processes under extreme precipitation is not yet clearly understood. Moreover, there is no precise theoretical understanding of the physical processes involved in heavy rainfalls (Carrega, 2004). Heavy rainfalls can be generated by different types of storms, from tropical cyclones to convective systems. Still, the number of types is greater than this, as the source and extent of extra-large rainfall vary from mountainous to inland continental and monsoon regions. In other words, the occurrence of these precipitation

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events is strongly dependent on the climatic range, which determines the amount and intensity of rainfall on a magnitude scale. On the physical side, it can estimate the severity and extent of the impact. It is also true even though the exceptional intensity of rainfall is typically concentrated in small areas (which is why it is difficult to give a regional assessment). Accordingly, very different extreme values can occur, and therefore, the concept of extra rainfall is assessed very differently in different regions. In the southern hemisphere, in New Zealand (in addition to the frequency of occurrence), heavy rain occurs when more than 50 mm falls in 6 h or more than 100 mm in 24 h (see NZraindanger). They judge the severity of the rainfall based on the expected occurrence and consequences. In the Swiss example, very different values are used due to the large differences in topography: a daily rainfall of 30 and 100 mm on the northern and southern exposed surfaces of the Alps, respectively, indicates only a modest hazard, compared to 80–120 mm/24 h and >160 mm/24 h which are considered as severe (see CHraindanger). According to the Hungarian assessment system, 20, 30 and 50 mm of rain falling in a short period represent the severity threshold values (see HUraindanger). These are the increments for intense rainfall, but in the event of a downpour, defined as a rainfall event (usually lasting 30–60 min, but up to 2–3 h), the amount of rainfall will exceed 25–30 mm. The EU also supports some regional (e.g. Interreg) and research (e.g. Clarity CSIS) projects, which mean hazard mapping in this respect. The measurements are based on high precipitation amounts, but the studies are always based on the resulting hazards (e.g. floods, flash floods) (see Interreg, Clarity). Climate change is expected to increase the number of extra precipitation events. According to most (regional) climate models, the most important element in this system is not the quantitative change in precipitation because the annual amount of precipitation does not change significantly, at least in Central Europe. However, there is variation within the year, with precipitation generally increasing by about 20% in the winter and decreasing by the same amount in the summer. The number of rainy days is predicted to decrease, implying an increase in intensity to the previous finding that helps the development of extreme values. While scientific understanding of the processes responsible for heavy rainfalls continues to improve, several challenges are associated with forecasting where, when and how much rainfall will occur (Ceresetti et al., 2012). Another question to be addressed for the future is whether there is a physical explanation for the occurrence of such statistically extreme events. In addition, these extra precipitation events are small in area and short in duration, making them difficult to predict and limiting the ability of numerical models to represent or predict the location and intensity of precipitation (National Weather Service; Schumacher, 2017). Responses to the threats posed by heavy and abundant rainfall can be summarised as preparation and precautions. In the longer term, better and more accurate precipitation hazard mapping can prepare by setting up the technical (measurement network, including radar technology) and methodological (statistical, including the management of inhomogeneous precipitation data) backgrounds. For shorter periods, the operation of alarm and warning systems is the most obvious solution. These systems are applied for extra meteorological values that

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could threaten living or non-living values in most regions and are usually available. It is internationally accepted to use yellow-orange-red colour codes to indicate danger. At the first (yellow) level, intense thunderstorms can result in large amounts of rainfall exceeding 25–30 mm per day over a small area. The second level (orange) is usually intense, with localised occurrences of more than 50 mm of rainfall. The level of warning varies from country to country; for example, in Hungary, there is no red level for downpours (but there is, for example, a yellow level with roughly the same amount of rainfall occurring over a short period). Still, for thunderstorms, there is (HUraindanger). Two limitations of rainfall forecasting are worth highlighting: the regional and intensity uncertainties of this point variable and the highly divergent nature of the signals from one region to another. Efforts to mitigate the effects of hail and hailstorms have been made since the Middle Ages. People in Europe tried to reduce the impact of hail by ringing bells or firing cannons. Protection is still an important (financial) part of agriculture today. Financial protection is an important issue because aerial, rocket or ground generator methods are usually expensive to invest in and maintain, so they are best used where hail protection pays off (e.g. protection of vineyards or orchards). Rocket control is based on the introduction of, for example silver iodide in acetone into the airspace where hail is likely to occur, and these particles attract water particles, creating numerous tiny ice grains which melt more easily as they move towards the ground. Such systems are also in operation in Hungary, for example, in Baranya County, where more than 200 automatic hail protection installations have reduced the area affected by hail and, despite the sometimes e20/ha protection costs, can result in significant savings (Molnár, 2016). Transport and especially aviation are also affected by the effects of hail. In this case, the use of early warning systems helps to prevent it (such as the METAR system for aviation).

3.3.4 Tornadoes A tornado is an air vortex with a few hundred metres or less cross section, resulting in significant consequences. Its formation is associated with updrafts (convection) and is related to the thunderstorm cloud. This whirlwind is relatively short-lived but can be very destructive. A key element in its formation is updraft, which can be caused by a conflux due to strong sunshine, topography or the appearance of a cold front or by wind shear. On the other hand, if the wind direction varies with height, the eddies can form due to wind shear. A supercell (“rotating thunderstorm”) can form with this rotation. In this case, the updraft lifts the air to a height of 10 km, where the intense (west–east direction) jet stream has a strong suction effect over the cell. The pressure difference between the cloud interior (low pressure) and its surroundings also helps the vortex form (Montz et al., 2017; NOAAtornado). Tornadoes are always associated with intense storm cells due to vertical air movements. In a tornado, the vortex reaches the ground surface—if not, it is called a tuba.

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Photo 3.4 Lightning and tornado in Hitting, North America (photo: Pexels, ralph-w-lambrecht)

Despite the studies, there are still a lot of questions to be answered about the exact cause of tornadoes (Bryant, 2005; Tornado Project Online, 2015). The size of the tornado funnel is a few 100 m, while the path taken by the vortex is usually a few km long (Photo 3.4). Many such tornadoes are known, usually of short duration, a few hours at most, but the vast majority of them are of low activity and cause little damage. These storms occur worldwide but are mainly concentrated in the temperate zone between latitudes 20 and 60° north and south of the Equator, so there are three to four hundred in Europe each year. The critical issues for the type and impact of tornadoes are wind velocity, the length of the path travelled by the vortex motion and the width of the funnel and for the damage they cause, the extent of the injuries and damage they cause. Concerning the parameters of tornadoes, the difficulty is to measure them. Large tornadoes can have multiple suction eddies, which have lower pressures that are difficult to measure and, consequently, even higher wind velocities. This high wind speed can reach up to 500 km/h on the outer wall of the funnel (Fig. 3.16). To classify tornadoes, the Fujita scale is used to match wind velocity and damage (Table 3.2). This scale starts from E0, indicating light damage and the lowest wind speed (105–137 km/h), while E5 indicates very serious damage and wind velocities above 322 km/h. Within each category, images of typical damage are used as a reference for observers (Fujita; Tornado Project Online, 2015). Tornadoes can occur at any time, but they are more frequent from the beginning of the warmer seasons, linked to the northward shift of the jet streams in spring. This position brings extreme weather systems closer together, pushing storms northwards

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Fig. 3.16 Measurements refer to the rotational speed of all vortices (A and C) and the forward speed along the ground (B). On the outer edge, the forward speed (~80 km/h) is combined with the tornado rotation speed (~160 km/h) and the suction vortex rotation speed (~160 km/h) (after Montz et al., 2017)

and increasing their number. The combination of extreme and variable wind speeds and wind direction can significantly contribute to tornadoes’ impact. The destructive power of tornadoes is further enhanced by the strong suction effect of the air funnel reaching the surface and the destructive effect of the dust and debris circulating at high speed (Table 3.3). The question in damage management is the usual one: what interventions can be used to reduce the impact (if we cannot talk about prevention)? This project can be done by taking useful preparations at home, at work or when travelling, for which many simple safety tips have been compiled (Tornado Project Online, 2015). On the other hand, there is a need to warn the public of the expected occurrence of severe thunderstorms with tornado threats, based on the professional basis of the weather forecasting agencies (NWF in the USA). The operation of tornado early warning systems dates back several decades, and the first in the USA was able to generate a forecast of about 10–15 min. Since then, significant technical and organisational advances (Doppler radar, new models) have at least doubled the warning time in numerous countries. Even so, it is clear that early warning can provide a very narrow time window for action.

3.3.5 Dust and Sandstorms A dust storm is formed in the context of a strong windstorm when large amounts of suspended solid minerals are transported in the air. There are three keywords in this interpretation, one of which is mineral, which also means that the particulate matter here is nothing other than, for example, cosmic or volcanic dust or possibly sea salt or smoke from an aerosol source. The other key issue is the mode of transport of

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Table 3.2 Enhanced Fujita scale using tornado wind speed and damagea Enhanced Fujita scale Wind speed (km/h) Potential damage F0 (weak)

105–137

Roofs can be damaged, gutters can fall down, tree branches can break off, and weak-rooted trees can fall. (Tornadoes that have no reported destruction are always considered F0)

F1 (moderate)

138–177

Roofs are torn up, doors are ripped off, windows are smashed, mobile homes are toppled

F2 (strong)

179–217

Roof structures are torn off, mobile homes are completely destroyed, large trees fall or are uprooted, small objects drift through the air, cars are lifted

F3 (significant)

219–266

Entire floors can disappear, major damage can occur to large buildings (e.g. shopping malls), train carriages can overturn, all trees in the path of the tornado can fall or break, heavier vehicles can be lifted and moved metres in the air

F4 (violent)

267–322

Buildings become level with the ground, with roof structures, wooden houses, vehicles and large objects constantly drifting in the air

F5 (devastating)

>322

Even multi-storey and reinforced concrete buildings collapse, and their pieces are scattered far and wide; heavy vehicles and their pieces fly hundreds of metres. Catastrophic destruction is everywhere (So far, a total of two F5 tornadoes has been recorded on the Fujita scale. The latest was in Parkersburg, Iowa, on 25 May 2008, which devastated half of the city)

a The

previous non-enhanced Fujita scale used wind speeds of 64–512+ km/h, and the enhanced one, mostly used since 2007, uses wind speeds of 105–322+ km/h, also divided into six categories Source Fujita Table 3.3 Damage caused by some tornadoes in 2011

Time

Number of fatalities

Damage caused (USD million)

Location

March

9

3500

USA

April

350

15,000

USA

May

176

14,000

USA

June

–

300

Denmark

September

1

300

Northern Europe

Source MURe (2019)

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the material. In Sect. 4.5, the compilation of the analysis of wind erosion shows the relationship between grain size, wind speed and the amount of material transported. It will also be seen that these materials can be transported in large quantities and over long distances. Depending on the size of the particles, the wind may transport the particles in a floating, bouncing or rolling motion. In the case of dust storms, it is called “floating transport”, and the World Meteorological Organization (WMO) formally interprets this process as one in which large amounts of dust entering the atmosphere reduce visibility to less than 1 km at eye level (1.8 m) (UNEP et al., 2016). In the event of a dust storm, the wind typically carries particles of about 0.05 mm in diameter, known as very fine sand or silt, depending on the grain size scale used. A third important issue in dust storms is the amount of transported material. The process is accompanied by medium and dry winds (40–100 km/h), but increasing wind speeds can significantly increase the amount of transported material. In terms of form, there is no strict distinction between sand and dust storms. The difference is that sandstorms transport larger grains that cannot be transported in a suspended manner due to their weight, so sand grains are typically transported by rolling and bouncing below 2 m in height. Therefore, it is understandable that they can move away from the source sand areas at a shorter distance, and the transported sand accumulates at the edge of the sand area. While a single major dust storm can transport up to 100 million tonnes of particulate matter over up to 1000 km, the transport distance for larger grain size sandstorms is only a few 10 km, but the amount of sand transported can be 2–3 billion tonnes per year. Sandstorms on Earth usually occur at low latitudes associated with deserts, i.e. sandstorms are essentially desert phenomena. On the other hand, dust storms are largely a product of arid areas with sparse vegetation and barren land, which provide a rich source of material for this process. The frequency map of dust and sandstorms over the last nearly forty years essentially outlines the areas that can be considered as sources (Fig. 3.17). The areas with the highest dust intensity (dust-producing),

Fig. 3.17 Estimates of dust storm frequency based on current synoptic weather data for the period January 1974–December 2012 (after Shao et al., 2013)

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where the material is produced partly by natural and partly by anthropogenic causes, are mainly located in the northern hemisphere: in the regions of North Africa, the Middle East, Southwest Asia and Northeast Asia, where both dust storm frequency and aerosol index (AI) values are the highest. The Sahara is undoubtedly the largest source of dust, the most important “hot spot”, with dust coming largely from natural sources (Feuerstein & Schepanski, 2018). It means billions of tonnes of minerals are blown and transported by wind from dry semi-arid areas every year. The North African areas where dust is blown out are responsible for 50–70% of global mineral dust production. Sandstorms are associated with desert environments and cannot move such distances. In the southern part of the Sahel, as well as in the Atlas Mountains and the coastal areas of the Mediterranean, dust blowing is of anthropogenic origin due to crop production and grazing. The sources of dust storms in the Middle East are of mixed origin, both natural and anthropogenic, while the dust in the Aral Sea is mainly of anthropogenic origin. The largest natural sources and important “hot spots” in Eastern Asia are in China, related to its basins and desert (UNEP et al., 2016; Zhang et al., 2016). The frequent dust and sandstorms in Central Asia are partly of natural origin and partly of anthropogenic origin due to the cultivation of sensitive soils. In North America, the greatest dust activity in the desert/semi-desert Great Basin region is of anthropogenic origin. Still, dust storms in the Prairie States are also notorious for causing significant damage in the 1930s, destroying the local economy and having major ecological consequences (Keller & DeVecchio, 2016). In the USA and Canada, this situation has been caused by severe drought and inappropriate agricultural practices (e.g. deep ploughing, efficient mechanisation and land use that increases wind speeds and vegetation clearance). The material from these dust sources can be transported by air masses over long distances of up to 10,000 km. Its effects affect the zone stretching from South America to Central Asia. Varga’s team presented the pathways of Saharan dust arriving in the Carpathian Basin and the extent of dust pollution (Varga et al., 2016) (see Fig. 3.18). The 2019 Saharan dust storm was particularly significant in the Carpathian Basin and across Europe. In this event, a southerly air current from Africa encountered a high-pressure air mass covering the central part of the continent and therefore

Fig. 3.18 Wind flow patterns at an altitude of 3000 m according to different Saharan dust event types (Varga, 2020)

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also diverted east–west, covering Europe with millions of tonnes of rock silt (Varga, 2020). Impacts of Dust and Sandstorms, Responses to Challenges Posed by Dust and Sandstorms, Trends in Changes Dust storms and dust deposition have a range of positive and negative environmental impacts, ranging from health effects to reduced crop yields and declining property values. Of these, the first to be highlighted are health impacts. Particularly in arid and semi-arid regions, the inhalation of fine particles can cause respiratory and infectious diseases or aggravate existing ones. It may result in increased mortality (EMDAT, 2019), and mortality rates are also very high at the global level due to premature mortality. Economic impacts include reduced crop yields, soil degradation or damage to infrastructure. In North Africa alone, dust storms cause financial losses of around $13 billion a year, while the damage caused by a single storm can also amount to hundreds of millions of dollars (World Bank, 2019). But in addition to economic damage, there is also often long-term environmental damage to vegetation or soil. Loss of surface vegetation results in increased exposure to wind, and intensive land use (e.g. vegetation clearance, deep ploughing) degrades the organic matter-rich soil layer near the surface, which plays an important role in maintaining soil stability and structure and reducing soil erodibility (UNEP et al., 2016). The transported dust covers very large areas. For example, dust originating in Africa can reach from the Amazon Basin to Florida (Keller & DeVecchio, 2016), and even the Hawaiian rainforest (UNEP et al., 2016), but has also been identified in many other locations. Its positive impact is that it can provide nutrients to terrestrial and ocean ecosystems, increase agricultural productivity and reduce the input of phosphorus into ecosystems. In general, it has a significant role in the terrestrial biogeochemical cycle. The input of dust into the climate system also alters the Earth’s radiation balance and can modify the effects of tropical cyclones (World Bank, 2019). An important goal for protection is to reduce the adverse effects of these dust storms. Today, the ability to predict sand and dust storms using sophisticated groundbased technologies, remote sensing data or a combination of these can significantly help. These methods offer the potential to develop and operate early warning systems. Over the last three decades, global annual dust emissions have increased by 25– 50%, partly due to land-use change and partly due to climate change (UNEP et al., 2016). Most of the value is due to climate change. A smaller proportion is due to anthropogenic effects, i.e. changes in land cover (but, dust storms can be prevented by abandoning farming or afforestation). Natural sources of dust have produced about three times as much as anthropogenic sources over the past 50 years. Over this period, there has been no significant change in dust storm activity in North Africa, the Middle East and South America, while the USA, Central Asia and Australia have seen significant increases. However, a calculation by Middleton (2019) shows a reduction in the number of dust storms in smaller sample areas in Africa. Future trends are difficult to predict with certainty, as climate change may affect different areas differently (mainly in terms of precipitation), but anthropogenic influences also point towards a reduction in dust formation.

3.4 Mapping and Forecasting Extreme Weather Events

131

3.4 Mapping and Forecasting Extreme Weather Events Extreme adverse weather events are predicted, collected, organised in databases and made available to users by several national and international organisations. Data on extreme climatic events (e.g. extreme temperatures, precipitation) are mostly collected at the national level, and this is also how hazards are forecasted. The aggregation of data for countries is ensured at the EU level by a dedicated database, and results for the status and forecasting of major meteorological (and other) hazards also exist at the EU level (e.g. drought or flood forecasts produced by the EU research institute in Ispra). What is missing is, for example, the aggregation of extreme climate events and their consequences. The European Severe Weather Database (ESWD) is a public database that describes and displays extreme weather events in text and on a map, daily for the EU (Fig. 3.19; Dotzek et al., 2009). These cover convective climate events such as whirlwinds, tornadoes, heavy rain, hail, snow or lightning, covering 11 categories in total (ESWD). The events are precisely defined, with their location given by latitude and longitude (usually with an accuracy of 700,000 people) during this period. The annualised data show a fluctuation in damage, while in 2018, 65 million people suffered from floods and 11,804 victims. The estimated damage was 131 billion US dollars (CRED, 2018a); the highest number of deaths was recorded in the 1999 floods in Venezuela (30,000 deaths), the 1980 floods in China (6200 deaths) and the 2013 floods in India (6000 deaths). The direct adverse effects of floods include, for example, the destruction of infrastructure elements or the cost of their reconstruction (e.g. buildings,

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transport routes). The extent of these damages is well documented in the EMDAT, CRED, NatCatService databases presented earlier. Still, the data may vary due to different interpretations of hazards and disasters (see Chap. 1.3). The most affected countries were in Asia, mainly China, India, Indonesia, Japan and Central America. These figures align with the areas affected by the 2018 floods (Disasters, 2018). Comparing the impacts on the living and non-living environment with the level of economic development (GDP per capita) in the 20-year data series, it can seem that countries with higher specific GDP suffered more significant material damage. At the same time, those with lower incomes were mainly affected by human life (Economic losses, 2019). Floods can also cause specific damage in coastal zones. Klaus Desmet and his co-authors predict that this could lead to a decline in GDP (and forced population movements) of several per cent per region over the coming decades (Desmet et al., 2018). There is a large literature on the direct, measurable impacts of floods, focusing mainly on the monetary material and immaterial losses in addition to the human impact. (However, few attempts have been made to quantify the positive impact of floods, although historically, for certain riverside societies, such as those along the Nile, Tigris or Euphrates rivers, which were also one of the cradles of population, the fertile soil-forming effects of floods were beneficial.) There is a similar difference of interpretation when assessing the direct intangible consequences. In addition to the damage to a much larger number of people, damage to cultural heritage and a substantial deterioration in the state of the ecosystem belong to these consequences. Floods also hurt mental health and human societies, but there is a lack of detailed studies and comprehensive evaluations on these issues. Flood risk management policy is hampered by the lack of a database that collects quantitative information on the wider health impacts of floods, even though these impacts can often have long-term and additional consequences. It is, therefore, no coincidence that affected people may see these health impacts as more important than financial losses (Fernandez et al., 2015). A good example of the indirect, tangible effects of flooding is the damage to the supply chain and the resulting damage. The 2011 floods in Thailand meant almost four months of outages in the supply of hard disc drives for computers from suppliers Toshiba, Western Digital (Bubeck et al., 2017). The vulnerability of these large chains and the serious, measurable economic damage they cause is illustrated by the 2013 floods in Europe forcing the closure of high-speed rail links in the regions of Berlin, Frankfurt am Main and Cologne. The relationship between flooding, its various health impacts and their severity is not yet well understood, but it is known that most of the physical health impacts occur in the weeks and months following the floods. These include infectious diseases caused by contaminated water or food, such as diarrhoea, cholera or hepatitis, which are more common in low-income countries (Hajat et al., 2005). However, psychological effects or other mental health disorders (such as post-traumatic stress disorder, depression and anxiety) can take years to develop (Lamond et al., 2015).

4.1 Flood Risk

147

4.1.5 Physical Consequences of Floods, Riverbed Formation The riverbed is expected to change relatively quickly when flooding occurs due to increased water discharge, higher water velocity and depth and higher gradients. Increased water volume has a greater erosion potential and can shape the riverbed. In the process, the river first picks up and transports fine and then coarser-grained sediment, but when the watercourse begins to subside and slow down, the coarser grains are deposited first. The above mentioned changes the morphometry of the river, for example, by cutting through a narrow bend, eroding sand- and gravel-bars and islands or creating bars along the riverbanks. As 1–10 mm of alluvium is deposited on the floodplain during a flood, the cross-sectional area of rivers is reduced, which means reduced drainage capacity (Nagy et al., 2017). Of course, the formation of a riverbed cannot only take place by flooding because the essential element of the form is always, simply put, the relationship between the water and the sediment it moves. Consequently, the significant incision can be measured in a lot of rivers today, despite the absence of bankfull or over-bankfull discharges. In several cases, this can be explained because there is less sediment to be transported. The river has energy left to deepen the bed (e.g. the Hungarian section of the Danube between Gy˝or and Budapest is incising to the sediment trapping in the reservoirs upstream). This deepening is also a good measure of the anthropogenic effects on the river, but it can also prevent water extraction and make bridges, for example, unstable.

4.1.6 Flood (Risk) Management and Mitigation The issue of flood management can be approached from several perspectives. Firstly, we can follow the same course for the hazards described earlier. Here again, the basic question is how and by what methods the extent of the hazard can be reduced. In this instance, relevant professional, technical, social and institutional responses to the flood hazards (as indicated in the previous points) must be provided. On the other hand, it is also possible to approach this question from the point of view of when and what action is needed to reduce the impact of the hazard in a reasonable time. These two approaches are combined in what follows. This approach may be a possible way of going beyond the usual proposals for dealing with floods and this type of hazard, which are generally true and acceptable: less sediment should be released into rivers, and the use of floodplains should be very limited, for example by moving all built structures out of them. For better flood management, the following tasks should be carried out before floods occur: • Calculation of the flood vulnerability of the area, for which very detailed methods were developed (Flood Resilience, Jongman et al., 2015). These questions largely

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Fig. 4.6 Regional extract of the flood risk exposure map. Source AQUEDUCT

•

•

•

•

cover the existence of plans, their consistency with other regulations, proposals for hazard mitigation, the existence of infrastructure and so on. Flood hazard mapping can also provide an appropriate professional response to the size and extent of the flood risk. Numerous countries also use hydrodynamic or LIDAR-based orographic mapping. A hazard map based on the Global Flood Analyser method, produced by the World Resources Institute with several collaborators, is shown in Fig. 4.6. In the model, which is essentially a demonstration model, the return period of flooding can be set (e.g. a return period of 100 years implies a probability of 1%), and the associated costs are estimated for a given year. In what follows, the conditions for a construction permit in some countries are described, including a demonstration of the flood hazard level of the parcel concerned. For several countries, an improved, higher resolution version of this model has been prepared (for the Carpathian Basin, for example, see Geoportal). The flood risk calculation is linked to the operation of complex hydrological monitoring networks (e.g. hydroinfo.hu), which, together with early warning systems (depending on the environmental status), can be considered as a relevant professional and institutional response to the hazard. Flood forecasts can provide probabilistic values for a few days or weeks for larger rivers, depending strongly on the type of flood, and are operational in most countries. In general, the planning of protection against emergencies and natural disasters and, in most cases, the preparation in the professional, infrastructural and organisational contexts are also among the preliminary tasks, which is also the response of society and the relevant institution to the flood event. Several solutions are known and used to reduce the impact of floods, all of which should be implemented in this preparatory phase: for example, raising flood protection dams, deepening the main riverbed, vegetation management in the floodplain, building emergency flood storage reservoirs, etc. Technical responses

4.1 Flood Risk

149

Fig. 4.7 To drain the floods more quickly, the meanders of the Tisza River (Hungary) were cut in several places, and a new bed was created, while the spreading of floods was prevented by the construction of flood protection levees (after Lászlóffy, 1982). A—artificial cut-off with the year of the cut; B—area prevented from flooding; C—levee built until 1860; D—levee built between 1879 and 1889; E—embankment section built after 1891; F—embankment abandoned after 1879; G—redundant levees, often create the framework of emergency reservoirs

include dredging (used in the Carpathian Basin since 1867) to increase the watercarrying capacity of the riverbed. An alternative means of flood protection, which must be implemented in advance, could be to divert a section of the watercourse into a new channel, regulate the river (Fig. 4.7) or build emergency reservoirs to store excess water or reduce the height of the flood level. Such emergency reservoirs have been built on the Seine since 1950, and five have been completed along the Tisza (Hungary) in recent decades, and five on the Yangtze so far, while the Yellow River floodwaters can be reduced using lakes (emergency reservoirs) around Wuhan, China. The continuous rise in water levels requires the regular raising of dams along the Tisza and its tributaries in Europe and on the certain Elbe or the Danube stretch. The question is: How far the dams can be raised to prevent rising floodwaters? The problem is that the rising flood levels increase the water pressure that the artificial embankment has to withstand and the occurrence of seepage under dams, which pose a significant threat to the stability of the dams. At the same time, the cost of raising the levees increases exponentially. It is more of a practical question that in this logical sequence, after each of the major floods on the Tisza (1876, 1895, 1930, 1970, 2001 and 2006), a decision was taken to raise the levees. Still, by the time it was completed, a new raising was necessary at some localities. This reason led to the construction of emergency reservoirs in several places (e.g. Tiszaroff, Tisza-Túr emergency reservoirs in Hungary).

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During a flood, protection is the primary task. During this response phase, technical, institutional and social tasks are typically required (see flood protection). One of the classic responses to flood risk was pumping, which was only possible along smaller watercourses and only after the technical conditions (e.g. steam engine) had been created. In lowland areas, a key element of protection is water drainage and the construction of dams and levees. The latter is often the key to flood protection. In the Carpathian Basin, a system of flood protection levees, built 100–150 years ago, along 3600 km of the Tisza River’s drainage system, provides safety for millions of inhabitants of some 400 settlements hundreds of thousands of houses and thousands of km of roads and railways. It is no coincidence that inspecting the condition of the levees and raising them in case of floods or increasing flood levels due to their confinement makes the regular raising of the barriers an important technical task. The expected deterioration of flood embankments built using old traditional technology, the sliding of the embankment material, the seepage through the dam and the loss of stability all require intervention. There are thousands of such precarious levee sections on the Hungarian levee failure of the Tisza, the weakness of which was brought to the surface by the floods, causing the dam in the Tivadar area (Upper Tisza, Hungary), which slipped in 2001, to have to be rebuilt. Work is still ongoing to raise some sections of the flood protection barriers. There are usually no flood protection levees in mountainous enclosed valleys. In such cases, mobile dams have been used successfully in many places since the early 2000s (from the USA to Germany) (Kádár, 2015; Pasche, 2005). In the case of a flood affecting a settlement, the respective mayor is in a decisionmaking position (in Hungary) and is able and entitled to decide on the possible emergency based on the professionally prepared results and the data of the early warning system. The mayor is also responsible for providing the name of the individual and organisation responsible for protection. Flood forecasts are of good quality in most countries, and this information is available to the public. Nevertheless, in this approach, the response is, on the one hand, both technical and engineering; on the other hand, managing and carrying out the administrative–institutional protection tasks: so that it is a social response to the emergency. Post-flood recovery involves technical and social tasks and related responses. A part of the social responses undoubtedly goes back to the period before the flooding. Indeed, securing the recovery costs and granting planning permission (or permission to build on large sites) often depend on institutional decisions. Insurance companies, for example, may later provide compensation or construction loans based on flood risk information, for which a flood risk map is a logical (and in some countries mandatory) source of data. In the USA, for example, this must be provided with any related federal loan application. Using the US example, the permitting process requires the identification of flood hazard areas, where permits are only granted if the flood hazard is below 1% (which is the flood elevation that recurs every 100 years). This type of regulation exists in other countries, of course, with the EU having adopted its Flood Risk Assessment and Management Directive under 2007/60/EC. In Hungary, too, the practice of flood risk management is fixed, covering risks affecting a property,

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151

human life, ecological status and cultural heritage and considering the related conflict locations (Risk Assessment, 2015). However, a societal response is more likely to be those systems that provide up-to-date, country-by-country information from scientific sources, as presented and allow for discussion (see ClimateChangePost). As with other natural hazards, floods can induce other processes, and together they can be integrated into a well-organised system. The interpretability of this sequence demonstrates (similarly to the hazards presented in Sects. 2.4 or 4.4) that one phenomenon is a kind of prelude to the occurrence of another. In this logical chain, precipitation triggers runoff (erosion), which generates (flash) floods, which can trigger slope mass movements (landslides), which can further increase the height and spatial extent of flooding.

4.1.7 Expected Trends in Flood Risk The future evolution of floods depends mainly on climate change. Its trend can only be estimated because it is influenced by numerous other factors, such as the human factor. It is no coincidence that the IPCC uses a range of scenarios. Due to the many factors of influence, current global flood risk forecasts are limited in their ability to integrate the combination of expected socio-economic development and climate change (Winsemius et al., 2016). Climate change-related climate variability is summarised in Chap. 7. On the natural side, changes in the extent and future magnitude of floods are mainly controlled because the atmosphere’s capacity to hold water increases with warming. Basically, due to the limited number of monitoring networks, the relationship between floods and larger-scale climate change can be inaccurately defined at regional scales. For Europe, it can be estimated from the database of historical floods and the modelled values of future changes that are typically increasing precipitation in the winter half-year may lead to increasing floods in north-western Europe, while mainly increasing evaporation may lead to decreasing floods in the medium and large catchments of Southern Europe, while decreasing snow cover and snowmelt due to warmer temperatures may lead to reduced floods in Eastern Europe (Blöschl et al., 2019; Fig. 4.8). Thus, large floods resulting from snowmelt and fed by the late spring precipitation maximum will be dispersed over time, and there will be less chance of large floods (Mez˝osi et al., 2013). Overall, the situation in Europe can be described as a slight increase (ca. 12%) in flooding in Central and Western Europe and a decrease (max. ~24%) in Eastern and Southern Europe. These results are very consistent with the figure (Fig. 4.5) resented earlier, showing the variation in annual river volumes over the last decades. Between 1980 and 2009, the number, frequency and magnitude of extreme floods increased globally, accompanied by an increase in the damage caused. It is generally estimated that a 1% increase in the area affected by flooding translates into a loss of around 2% of GDP (see European Commission, 2014). Flood risk can vary greatly from region to region. While Europe and the USA have seen the strongest increases in flooding over the past three decades, Brazil and Australia have seen the least increase

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Fig. 4.8 Flooding trends in Europe over the past five decades, in percentage (%)—colours indicate the magnitude of the expected change in flooding (based on Blöschl et al., 2019)

in flood risk (Berghuijs, 2017). In Russia, flooding has increased in the Asian part of the country, while flood intensity in the European part has decreased significantly since the mid-twentieth century (Frolova et al., 2017). However, the causes of shortterm variability or the physical explanations for long-term changes have not yet been explored sufficiently, as the drivers of these processes are very different. Accurate analysis and modelling of large and infrequent floods can be of considerable help in this forward-thinking. Models that integrate socio-economic, hydrological and climate scenarios exist for flood risk. If no action is taken to mitigate the impacts at the global level, these models estimate the damage caused by the hazards to be twenty times higher by the end of the century than today (Winsemius et al., 2016). The results of the models run on several natural (climate) and social (HadCM3 and SRESA1b) parameters suggest that by 2050, the 100-year maximum discharge could become twice as frequent. This flood hazard could affect 40% of the Earth, i.e. about 450 million people and about 430,000 km2 of land (Arnell & Gosling, 2016). Climate change particularly affects countries in South-East Asia (e.g. India, Bangladesh or Indonesia) and Africa, which are highly vulnerable to flooding, where low GDP also makes protection difficult. However, investing in flood management and improving adaptation are beneficial and profitable for countries with lower specific incomes and important for richer regions.

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153

4.2 Flash Floods Flash floods are a specific type of flood hazard and disaster. As small watercourses leave their beds, their discussion logically fits flood hazards. Still, the increasing frequency of flash floods and the growing extent of their damage justify a separate chapter. The natural hazard of floods is the most frequent in Europe today (CRED, 2018b; IPCC, 2018). Compared to the systems of floods (Sect. 4.1), flash floods differ from floods on larger rivers in intensity, size, duration, spatial extent and location and response to the hazard, although the damage caused is similar (Czigány et al., 2010; Economic losses, 2018; EMDAT, 2019). Flash floods are caused by the inability of the soil to absorb the large volume of water that is produced in a short period, so it flows down the slope and valley floor from the relatively steeply sloping catchment quickly, with a high discharge compared to the natural discharge of the stream and a lot of sediment. But its formation and impact are still a more complex issue, despite the simple definition used by NOAA. According to it, flash floods begin within six hours, often within three hours, following heavy rains (or other similar causes) (see NOAA NWS3). The onset and course of flash floods are influenced by several factors but are most often triggered by heavy rainfall or damage to dams built perpendicular to watercourses. Water flowing down at high velocities can also carry a lot of debris, so flash floods show a gradual transition towards debris and mudflow phenomena, which in turn are mass movements (Lorente et al., 2003), indicating that these floods are associated with significant sediment transport. Flash floods are also called pluvial floods, distinct from traditional fluvial floods. The distinction is understandable, but the name is poorly justified because it seems as if fluvial floods are not essentially caused by precipitation. One of the distinctive differences is the intensity of the flooding. In general, flood intensity expresses the amount of water that flows across the cross section of the riverbed/floodplain per unit time. Flash floods show much higher peaks in the discharge/time cross section (see Table 4.2), representing the runoff of large amounts of water in a short period. In addition to excessive precipitation, this is also since the surface is steep or covered with artificial material (e.g. buildings, asphalt) or has sparse vegetation. Hence, the potential for infiltration and sequestration of water is very modest. Deforestation in the drainage basin can increase runoff by 10%, but this can be much higher for flash floods. Artificial alteration of potential infiltration and runoff areas can increase flash flood risk, particularly in urban areas. In these areas, runoff is faster and therefore more powerful, and the damage is more severe due to limited infiltration (Photo 4.1a and b), which is why it is necessary to build and regularly maintain drainage systems with suitable cross sections in the affected settlements (Keller & DeVecchio, 2016; Vadillo, 2019).

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Photo 4.1 a Devastation of a flash flood (2005) in Mátrakeresztes, North-Hungary (Source viharvadaszok.hu). b Condition after reconstruction (2015) in Mátrakeresztes (own photo)

4.2.1 Spatial and Temporal Characteristics of Flash Floods Flash floods are not large and are associated with catchments averaging a few 10– 1000 km2 , but their formation is highly dependent on topography. Flash floods typically form in rivers’ upper, erosional reaches (Fig. 4.4: Zone 1). In addition to rainfall intensity, distribution and topographic parameters (e.g. slope gradient, valley density), the nature of flash floods varies sensitively depending on the type and

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155

thickness of the soil and, in particular, its water content. A moisture condition close to saturation in a given drainage basin facilitates rapid runoff, as infiltration is limited in such cases. Other important determinants are the type of land use, including the type and density of vegetation cover, the anthropogenic land cover and the presence of landforms that impede (e.g. field margins, forest strips) or facilitate (e.g. straight channels, perpendicular ploughing) runoff. At the drainage basin scale, these processes occur locally, mainly in the upper part of small catchments, in the erosion sections of watercourses. Globally, flash floods occur up to the 60° latitude, north of which (in this hemisphere), the risk is reduced, similarly to floods, mainly for climatic reasons. This situation is also reflected in the flash flood intensity index, although it mostly measures the natural conditions and consequences after the event (Schroeder et al., 2016). In Europe, south of the 60° latitude, the Mediterranean and Southern Europe are particularly affected by this risk. However, it is very difficult to conclude on such a large scale because the process is small in size (Anquetin et al., 2010). However, it is no coincidence that these areas associated with flash floods are analysed in the dozens of peer-reviewed papers published in the Journal of Hydrology in 2012 (Volume 394) and 2016 (Volume 571). The damage caused by the impact described later also typically occurs in areas with semi-arid climates. Flash floods do not necessarily require large rainfall events of many hundreds of mm. However, they are mainly associated with infrequent, high-intensity rainfall events (60–150 mm). Still, their development is influenced by topographic, soil, land use and anthropogenic (e.g. settlement, mining) conditions that support rapid runoff of rainwater. In Europe, there is a seasonal variation in the frequency of flash floods between the Mediterranean Sea and the Black Sea, which is characterised by a higher frequency of flash floods, and in the Mediterranean region (Marchi et al., 2010). According to this, flash floods are most frequent in autumn in the Mediterranean and AlpineMediterranean regions, while in continental mainland regions, they usually occur in summer. The occurrence of flash floods in the Carpathian Basin due to infrequent and extreme precipitation intensity is not always related to the observed early summer precipitation maximum in the region. Moreover, the latter is measured to be shifted (Parajka et al., 2010).

4.2.2 Effects of Flash Floods and the Damage They Cause Floods are the most common cause of environmental damage in Europe. Although flash floods tend to occur in small catchments, in Europe alone, they cause major losses in an average of fifty to one hundred cases per year and account for 70% of all flood-related deaths (Pino et al., 2016). On a global scale, a significant proportion of the 5,000 deaths a year linked to floods are attributable to flash floods (WMO 2019). Based on databases collected in nature (some of which are described in Chap. 1), half of the approximately 1,500 floods recorded since 1870 were flash floods (Paprotny et al., 2018). The fatalities occur mainly in the Mediterranean Sea countries, where

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coastal areas have a high population density due to urbanisation in recent decades. It is the cause why they are referred to as “urban flooding” when flash floods affect such populated areas. Almost 90% of flood victims in Spain are killed by flash floods (Journal of Hydrology, 2012, special issue). Flash floods have also become a frequent topic in the news due to the human and infrastructural damage caused (e.g. traffic disruptions, damage to buildings and other properties, disruptions to electricity, potable water supply and wastewater drainage) (FF1-4). Flash flood hazards are usually smaller, affecting catchments of a few 10–100 km2 , and thus, a detailed analysis is in principle possible. The difficulty is the larger number of catchments at risk. Several small drainage basins have now been analysed, and more comprehensive studies have been carried out (pl. Czigány et al., 2010; Anquetin et al., 2010; Lorente et al., 2003; Flash-floods-Europe, 2018). Petersen (2001) summarised the social, economic and environmental damage affecting many people. The IPCC provides information on flash floods for European countries based on data from the European Environment Agency and other data sources (EuropeFF, 2019). The financial damage to larger areas is not well known and difficult to estimate comprehensively without data (Economic losses, 2019). Excessive rainfall and its intensity are the main causes of flash floods, which cause the highest number of casualties. The highest fatality rate was caused by a flash flood in 1979 when the Machchhu River dam burst through the valley dyke near the Indian town of Morbi (Table 4.3). The flash flood-prone areas of Saudi Arabia and eastern Ethiopia are located at almost the same latitude and in a similarly semi-arid climate. The events with the highest casualties are included in the FFlist2019 collection. As an indication of the extent of the damage caused by flash floods, in Rapid City (USA), Table 4.3 Documented flash floods with the highest number of deaths Date of the event Number of victims Cause of the flash flood

Geographical location

11.08 1979

1,800–25,000

Dam failure due to excessive rainfall

Machchhu River, the town of Morbi (India)

25.11.1967

464

Excessive rainfall: about 125 mm of rain fell in 5 h

Lisboa (Portugal)

06.08.2006

350

Excessive rainfall

The city of Dire Dawa (eastern Ethiopia)

13.08.2006

125

Excessive rainfall

Omo River (eastern Ethiopia)

24.07.1982

299

Excessive rainfall: 187 mm of rain fell in 4 h

Nagasaki (Japan)

09.06.1972

238

Dam failure due to Rapid City, Black Hills excessive rainfall: 380 mm flood (USA, South Dakota) fell in six hours

25.11.2009

>100

Excessive rainfall

Jeddah (Saudi Arabia)

01.04.2013

101

Excessive rainfall

Buenos Aires Province (Argentina)

Source FFlist (2019)

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157

not only were around 1500 houses severely damaged but around 5000 cars were washed away. A flash flood was caused by a breach in the red sludge reservoir near Kolontar, which flooded several villages in 2010 and killed nine people.

4.2.3 Estimation of Flash Flood Risk The flash flood hazard map is produced partly for status determination and partly for planning and protective forecasting purposes. They can be prepared using different parameters depending on the purpose. One commonly used method is calculating flash flood potential, produced by the NWC (National Weather Centre) and NOAA (FFPI, 2006). In this method, the values of four parameters (slope gradient, vegetation density, land use and soil type) are treated as the values of a quadratic grid overlaid on the study area, and the maps are overlaid on each other using a simple GIS technique. The most important parameter is the slope gradient, which is weighted, but it is presented as an equally weighted parameter for simplicity in the example below. The values are grouped into four categories, and this is how the square is given its value. The second parameter considered is forest density, the third is land use, which in practice refers to the type of land cover (referring to its water retention capacity). The fourth parameter classifies the soil type, referring to the infiltration capacity of the soil based on its mechanical composition (Fig. 4.9). The potential hazard index of flash floods is also tested as an early warning system (2–3 days in advance) in several states (NWC). The problem with this approach is that the precipitation forecast is uncertain; recent radar technology analyses can only give a credible estimate of cloud saturation about half an hour before the event. The calculation used in Hungary uses fewer parameters, but their relationship to flash flooding is well documented (FFNWS). The calculation includes four categories Fig. 4.9 Flash flood index expresses the risk of a flash flood (NWC/NOAA) using the example of the Fork Virgin watershed (USA)

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Fig. 4.10 Spatial differences in flash flood risk concerning small catchments (Blanka and Mez˝osi, 2012)

for slope gradient (0 point: 30%), three categories for surface permeability for silt and clay content (1 point: 0–40%; 2 points: 40–80%; 3 points: > 80%) and three categories for forest cover (3 points: 0–20%; 2 points: 20–50%; 1 point: