IPCC_Managing Risks of Extreme Events.pdf - Climate Access

Chapter 4Changes in Impacts of Climate Extremes: Human Systems and Ecosystems4.1. IntroductionChapter 3 evaluates observed and projected changes in the frequency,intensity, spatial extent, and duration of extreme weather and climateevents. This physical basis provides a picture of climate change andextreme events. But it does not by itself indicate the impacts experiencedby humans or ecosystems. For example, for some sectors and groups ofpeople, severe impacts may result from relatively minor weather andclimate events. To understand impacts triggered by weather and climateevents, the exposure and vulnerability of humans and ecological systemsneed to be examined. The emphasis of this chapter is on negativeimpacts, in line with this report’s focus on managing the risks of extremeevents and disasters. Weather and climate events, however, can and oftendo have positive impacts for some people and ecosystems.In this chapter, two different types of impacts on human and ecologicalsystems are examined: (i) impacts of extreme weather and climateevents; and (ii) extreme impacts triggered by less-than-extreme weatheror climate events (in combination with non-climatic factors, such ashigh exposure and/or vulnerability). Where data are available, impactsare examined from sectoral and regional perspectives. Throughout thischapter, the term ‘climate extremes’ will be used to refer in brief to‘extreme weather and extreme climate events,’ as defined in theGlossary and discussed more extensively in Section 3.1.2.Activities undertaken as disaster risk reduction may also act as adaptationto trends in climate extremes resulting from climate change, and theymay thereby act to reduce impacts. Strategies to reduce risk from onetype of climate extreme may act to increase or decrease the risk fromanother. In writing this chapter, we have not considered these issues assubsequent chapters are dedicated to adaptation. Here, impacts areassessed without discussion of the specific possible adaptation or disasterrisk reduction strategies or policies evaluated in subsequent chapters.Examination of trends in impacts and disasters highlights the difficultiesin attributing trends in weather- and climate-related disasters to climatechange. Trends in exposure and vulnerability and their relationship withclimate extremes are discussed. The chapter then examines system- andsector-based aspects of vulnerability, exposure, and impacts, bothobserved and projected. The same issues are examined regionally beforethe chapter concludes with a section on the costs of weather- andclimate-related impacts, disasters, and adaptation.4.2. Climatic Extremes in Naturaland Socioeconomic Systems4.2.1. How Do Climate Extremes Impacton Humans and Ecosystems?The impacts of weather and climate extremes are largely determined byexposure and vulnerability. This is occurring in a context where all threecomponents – exposure, vulnerability, and climate – are highly dynamicand subject to continuous change. Some changes in exposure andvulnerability can be considered as adaptive actions. For example, migrationaway from high-hazard areas (see Chapter 1 and the Glossary for adefinition of the term ‘hazard’) reduces exposure and the chance ofdisaster and is also an adaptation to increasing risk from climateextremes (Adger et al., 2001; Dodman and Satterthwaite, 2008; Revi,2008). Similar adaptive actions are reflected in changes in buildingregulations and livelihoods, among many other examples.Extreme impacts on humans and ecosystems can be conceptualized as‘disasters’ or ‘emergencies.’ Many contemporary definitions emphasizeeither that a disaster results when the impact is such that local capacityto cope is exceeded or such that it severely disrupts normal activities.There is a significant literature on the definitional issues, which includefactors of scale and irreversibility (Quarantelli, 1998; Handmer andDovers, 2007). Disasters result from impacts that require both exposureto the climate event and a susceptibility to harm by what is exposed.Impacts can include major destruction of assets and disruption toeconomic sectors, loss of human lives, mental health effects, or loss andimpacts on plants, animals, and ecosystem services. The Glossary providesthe definition of disaster used in this chapter.Exposure can be conceptualized as the presence of human and ecosystemtangible and intangible assets and activities (including services) in areasaffected by climate extremes (see Sections 1.1.2 and 2.2 and theGlossary for definitional discussion). Without exposure there is noimpact. Temporal and spatial scales are also important. Exposure can bemore or less permanent; for example, exposure can be increased bypeople visiting an area or decreased by evacuation of people andlivestock after a warning. As human activity and settlements expandinto an exposed area, more people will be subject to and affected bylocal climatic hazards. Population growth is predominantly in developingcountries (Peduzzi et al., 2011; UNISDR, 2011). Newly occupied areasaround or in urban areas were previously left vacant because they areprone to the occurrence of climatic hazards (Handmer and Dovers,2007; Satterthwaite et al., 2007; Wilbanks et al., 2007), for example withmovement of squatters to and development of informal settlements inareas prone to flooding (Huq et al., 2007) and landslides (Anderson etal., 2007). ‘Informal settlements’ are characterized by an absence ofinvolvement by government in planning, building, or infrastructure andlack of secure tenure. In addition, there are affluent individuals pursuingenvironmental amenity through coastal canal estates, riverside, andbush locations, which are often at greater risk from floods and fires(Handmer and Dovers, 2007).Exposure is a necessary but not sufficient condition for impacts. Forexposed areas to be subjected to significant impacts from a weather orclimate event there must be vulnerability. Vulnerability is composed of(i) susceptibility of what is exposed to harm (loss or damage) from theevent, and (ii) its capacity to recover (Cutter and Emrich, 2006; seeSections 1.1.2 and 2.2 and the Glossary). Vulnerability is defined here asin the Glossary as the propensity or predisposition to be adverselyaffected. For example, those whose livelihoods are weather-dependent237