Severe Convective Storm Risk in the Eastern Cape Province of South Africa
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SEVERE CONVECTIVE STORM RISK IN THE EASTERN CAPE PROVINCE OF SOUTH AFRICA A thesis submitted in fulfilment of the requirements for the degree of DOCTOR OF PHILOSOPHY of RHODES UNIVERSITY by DESMOND MARK PYLE November 2006 ABSTRACT This study investigates the temporal, spatial and impact characteristics of severe convective storm hazard and risk in the Eastern Cape Province of South Africa. Using historical data on severe convective storms dating from 1897, patterns of the hazard threat and risk to various geographic populations were investigated. A conceptual framework that emphasises the combined role hazard and vulnerability play in defining risk was used for the study. A methodology for ranking the severity of the storms in the historical dataset, based on recorded damage/impact, was specifically developed for the study. It is intended that this methodology will have a potentially wider application and may be adapted to a range of hazard impact and risk studies in South Africa and internationally. The study was undertaken within the context of the South African Disaster Management Act of 2002. Findings of the study show that severe convective storms can occur throughout the province, but there are clearly demarcated areas of higher frequency and concentration. The impact of storms is particularly severe on impoverished and vulnerable rural populations in the eastern parts of the province, where there is an urgent need for building capacity in disaster risk management. A major outcome of the study is the production of a severe convective storm hazard/risk map of the Eastern Cape, which it is hoped will be of benefit to a number of stakeholders in the province, particularly disaster management, but also the South African Weather Service, agricultural organisations, development/planning authorities, educational authorities and risk insurers. It is hoped that this map and the study in general will assist in guiding the operational responses of the various authorities, especially in terms of those interventions aimed at disaster risk reduction in the Eastern Cape. ii ACKNOWLEDGEMENTS I wish to express my sincere gratitude to my supervisor, Professor Kate Rowntree, for her support, advice and encouragement while completing this thesis. I am deeply grateful to the following persons who have also provided invaluable support and assistance during the past number of years: Dr Shamsuddin Shahid for GIS assistance (Figures 14-18; 25-29; 32-34; 36; 40-57). Mrs Susan Abraham for assistance in preparing the diagrams in this thesis (Figures 1-11; 13). Professor Etienne Nel for helpful comments and unfailing encouragement. Dr Matthew Gibb for assistance with the final editing and layout of this thesis. Ms Lisl Griffioen for proofreading this thesis. Mr Hugh van Niekerk and Mr Garth Sampson for climate information and technical advice from the South African Weather Service in Port Elizabeth. Finally, to my wife, Sue and my children, Andrew, Michael and Serena, who have endured many years of my research and writing with great forbearance. I would not have been able to complete this thesis without their selfless support and encouragement; this thesis is as much theirs as it is mine. iii TABLE OF CONTENTS ABSTRACT .................................................................................................................................... ii ACKNOWLEDGEMENTS ........................................................................................................... iii TABLE OF CONTENTS ............................................................................................................... iv TABLE OF TABLES................................................................................................................... viii TABLE OF FIGURES ................................................................................................................... ix ACRONYMS ................................................................................................................................. xi CHAPTER ONE: INTRODUCTION ..............................................................................................1 1.1 Background to the study.........................................................................................................1 1.2 Problem identification/definition ...........................................................................................2 1.3 Purpose, goals and objectives of the study.............................................................................3 1.3.1 Purpose ...........................................................................................................................3 1.3.2 Goals/broad objectives....................................................................................................3 1.3.3 Objectives .......................................................................................................................4 1.4 Limitations to the study..........................................................................................................4 1.5 Conceptual framework...........................................................................................................5 1.6 The structure of the study.......................................................................................................7 CHAPTER TWO: NATURAL HAZARDS, DISASTERS AND RISK..........................................9 2.1 Introduction............................................................................................................................9 2.2 The impact of natural hazards and disasters...........................................................................9 2.3 Natural hazards, disasters and risk: theoretical and conceptual frameworks and models....10 2.4 Key definitions.....................................................................................................................15 2.5 Summary ..............................................................................................................................17 CHAPTER THREE: SEVERE CONVECTIVE STORM HAZARDS..........................................18 3.1 Introduction..........................................................................................................................18 3.2 Classification schemes .........................................................................................................18 3.3 Severe convective storms: a problem of definition..............................................................19 3.4 Thunderstorm types and models of development ................................................................21 3.5 Thunderstorm hazards..........................................................................................................25 3.5.1 Damaging winds ...........................................................................................................26 3.5.1.1 Tornadoes ..............................................................................................................26 3.5.1.2 Downbursts, gust fronts, straight-line winds and derechoes .................................28 3.5.2 Hail ...............................................................................................................................30 3.5.3 Lightning.......................................................................................................................31 3.5.4 Flash floods...................................................................................................................33 3.6 Measuring intensity and severity of severe storms ..............................................................33 3.6.1 Tornado intensity..........................................................................................................33 3.6.2 Hail intensity.................................................................................................................35 3.6.3 Other intensity and severity indices..............................................................................36 iv 3.7 Trends in severe convective storm research.........................................................................37 3.7.1 International scenario....................................................................................................37 3.7.2 South Africa: background on severe storm incidence ..................................................38 3.7.3 Local response: A review of South African research in the field .................................40 3.7.4 A review of recent frameworks and methodologies in severe storm and hazards research..................................................................................................................................47 3.7.4.1 International...........................................................................................................47 3.7.4.2 South Africa ..........................................................................................................51 3.8 Summary ..............................................................................................................................55 CHAPTER FOUR: DISASTER RISK MANAGEMENT: INTERNATIONAL, AFRICAN AND SOUTH AFRICAN DEVELOPMENTS........................................................................................56 4.1 Introduction..........................................................................................................................56 4.2 International context and