IPCC_Managing Risks of Extreme Events.pdf - Climate Access

Chapter 4Changes in Impacts of Climate Extremes: Human Systems and EcosystemsThe statement about the absence of trends in impacts attributableto natural or anthropogenic climate change holds for tropical andextratropical storms and tornados (Boruff et al., 2003; Pielke Jr. et al.,2003, 2008; Raghavan and Rajesh, 2003; Miller et al 2008; Schmidt et al.,2009; Zhang et al., 2009; see also Box 4-2). Most studies related increasesfound in normalized hurricane losses in the United States since the1970s (Miller et al., 2008; Schmidt et al., 2009; Nordhaus, 2010) to thenatural variability observed since that time (Miller et al., 2008; Pielke Jr. etal., 2008). Bouwer and Botzen (2011) demonstrated that other normalizedrecords of total economic and insured losses for the same series ofhurricanes exhibit no significant trends in losses since 1900.The absence of an attributable climate change signal in losses also holdsfor flood losses (Pielke Jr. and Downton, 2000; Downton et al., 2005;Barredo, 2009; Hilker et al., 2009), although some studies did find recentincreases in flood losses related in part to changes in intense rainfallevents (Fengqing et al., 2005; Chang et al., 2009). For precipitationrelatedevents (intense rainfall, hail, and flash floods), the picture ismore diverse. Some studies suggest an increase in damages related toa changing incidence in extreme precipitation (Changnon, 2001, 2009),although no trends were found for normalized losses from flash floodsand landslides in Switzerland (Hilker et al., 2009). Similarly, a study ofnormalized damages from bushfires in Australia also shows that increasesare due to increasing exposure and wealth (Crompton et al., 2010).Increasing exposure of people and economic assets has been the majorcause of long-term increases in economic losses from weather- andclimate-related disasters (high confidence). The attribution of economicdisaster losses is subject to a number of limitations in studies to date:data availability (most data are available for standard economic sectorsin developed countries); type of hazards studied (most studies focus oncyclones, where confidence in observed trends and attribution ofchanges to human influence is low; Section 3.4.4); and the processesused to normalize loss data over time. Different studies use differentapproaches to normalization, and most normalization approaches takeaccount of changes in exposure of people and assets, but use only limited,if any, measures of vulnerability trends, which is questionable. Differentapproaches are also used to handle variations in the quality andcompleteness of data on impacts over time. Finding a trend or ‘signal’in a system characterized by large variability or ‘noise’ is difficult andrequires lengthy records. These are all areas of potential weakness inthe methods and conclusions of longitudinal loss studies and moreempirical and conceptual efforts are needed. Nevertheless, the results ofthe studies mentioned above are strengthened as they show similarresults, although they have applied different data sets and methodologies.A general area of uncertainty in the studies concerns the impacts ofweather and climate events on the livelihoods and people of informalsettlements and economic sectors, especially in developing countries.Some one billion people live in informal settlements (UNISDR, 2011),and over half the economy in some developing countries is informal(Schneider et al., 2010). These impacts have not been systematicallydocumented, with the result that they are largely excluded from bothlongitudinal impact analysis and attribution to defined weatherepisodes.Another general area of uncertainty comes from confounding factorsthat can be identified but are difficult to quantify, and relates to theusual assumption of constant vulnerability in studies of loss trends.These include factors that would be expected to increase resilience(Chapters 2 and 5 of this report) and thereby mask the influence ofclimate change, and those that could act to increase the impact ofclimate change. Those that could mask the effects of change includegradual improvements in warnings and emergency management (Adgeret al., 2005), building regulations (Crichton, 2007), and changinglifestyles (such as the use of air conditioning), and the almost instantmedia coverage of any major weather extreme that may help reducelosses. In the other direction are changes that may be increasing risk,such as the movement of people in many countries to coastal areasprone to cyclones (Pompe and Rinehart, 2008) and sea level rise.4.5.4. Assessment of Impact CostsMuch work has been conducted on the analysis of direct economic lossesfrom natural disasters. The examples mentioned below mainly focus onnational and regional economic losses from particular climate extremesand disasters, and also discuss uncertainty issues related to the assessmentof economic impacts.4.5.4.1. Estimates of Global and Regional Costs of DisastersObserved trends in extreme impacts: Data on global weather- andclimate-related disaster losses reported since the 1960s reflect mainlymonetized direct damages to assets, and are unequally distributed.Estimates of annual losses have ranged since 1980 from a few US$billion to above 200 billion (in 2010 dollars) for 2005 (the year ofHurricane Katrina) (UNISDR, 2009; Swiss Re 2010; Munich Re, 2011).These estimates do not include indirect and intangible losses.On a global scale, annual material damage from large weather andclimate events has been found to have increased eight-fold between the1960s and the 1990s, while the insured damage has been found to haveincreased by 17-fold in the same interval, in inflation-adjusted monetaryunits (Mechler and Kundzewicz, 2010). Between 1980 and 2004, thetotal costs of extreme weather events totaled US$ 1.4 trillion, of whichonly one-quarter was insured (Mills, 2005). Material damages caused bynatural disasters, mostly weather- and water-related, have increasedmore rapidly than population or economic growth, so that these factorsalone may not fully explain the observed increase in damage. The lossof life has been brought down considerably (Mills, 2005; UNISDR, 2011).Developing regions are vulnerable both because of exposure toweather- and climate-related extremes and their status as developingeconomies. However, disaster impacts are unevenly distributed by type of269