IPCC_Managing Risks of Extreme Events.pdf - Climate Access

Changes in Impacts of Climate Extremes: Human Systems and EcosystemsChapter 4Box 4-2 | Observed and Projected Trends in Human Exposure: Tropical Cyclones and FloodsThe International loss databases with global coverage such as EM-DAT, NatCat, and Sigma (maintained by the Centre for theEpidemiology of Disasters, Munich Re, and Swiss Re, respectively) present an increase in reported disasters through time. Although thenumber of reported tropical cyclone disasters, for example, has increased from a yearly average of 21.7 during the 1970s to 63 duringthe 2000s (see Table 4-1), one should not simply conclude that the number of disasters is increasing due to climate change. There arefour factors that may individually or together explain this increase: improved access to information, higher population exposure, highervulnerability, and higher frequency and/or intensity of hazards (Dao and Peduzzi, 2004; Peduzzi et al., 2009). Due to uncertainties in thesignificance of the role of each of these four possible factors (especially regarding improved access to information), a vulnerability andrisk trend analysis cannot be performed based on reported losses (e.g., from EM-DAT or Munich Re). To better understand this trend,international loss databases would have to be standardized.Here for both tropical cyclones and floods, we overview a method for better understanding these factors through calculation of pasttrends and future projections of human exposure at regional and global scales. Changes in population size strongly influence changes inTable 4-1 | Trend in tropical cyclone disasters reported versus tropical cyclones detectedby satellite during the last four decades. The reported disasters as a percentage of thenumber of countries hit by tropical cyclones increased three-fold. Note that ‘best trackdata’ generally comprise four-times daily estimates of tropical cyclone intensity andposition; these data are based on post-season reprocessing of data that were collectedoperationally during each storm’s lifetime. Source: UNISDR, 2011.Number of tropical cyclonesas identified in best trackdata (average per year)Number of countries hit bytropical cyclones as detectedby satellite (average per year)Number of disasters triggeredby tropical cyclones asreported by EM-DAT (averageper year)Reported disasters as apercentage of number ofcountries hit by tropicalcyclones1970 - 79 1980 - 89 1990 - 99 2000 - 0988.4 88.2 87.2 86.5142.1 144.0 155.0 146.321.7 37.5 50.6 63.015% 26% 33% 43%exposure to hazards. It is estimated that currently about 1.15billion people live in tropical cyclone-prone areas. The physicalexposure (yearly average number of people exposed) to tropicalcyclones is estimated to have increased from approximately73 million in 1970 to approximately 123 million in 2010(Figure 4-1; Peduzzi et al., 2011). The number of times thatcountries are hit by tropical cyclones per year is relativelysteady (between 140 and 155 countries per year 1 on average;see Table 4-1 (UNISDR, 2011).In most oceans, the frequency of tropical cyclones is likely todecrease or remain unchanged while mean tropical cycloneContinued next page____________1 This is the number of intersections between countries and tropical cyclones.One cyclone can affect several countries, but also many tropical cyclonesoccur only over the oceans.125,95068,0004,8702,610NORTHAMERICAAverage Physical Exposureto Tropical CyclonesAssuming Constant Hazardin thousands of people per yearin 2030in 1970Circles are proportionalto the number of persons affected10030CENTRAL ANDSOUTH AMERICA3,4901,910ISLANDSIndian Ocean, Pacific Ocean,Caribbean and other IslandsAFRICA2,280500ASIA10050AUSTRALIANEW ZEALANDFigure 4-1 | Average physical exposure to tropical cyclones assuming constant hazard (in thousands of people per year). Data from Peduzzi et al., 2011.240