Population exposure to precipitation extremes in the Indus River Basin at1.5℃,2.0℃and 3.0℃warming levels

Adverse effects of extreme events are the major focus of climate change impact studies.Precipitation-related extremes has substantial so-cioeconomic impacts under the changing climate.Quantifying population exposure to precipitation extreme is the fundamental aspect ofpopulation risk assessments in the climate hotspot of Indus River Basin.This study investigates the population exposure to precipitation ex-tremes at 1.5℃,2.0℃,and 3.0℃global warmings in the Indus River Basin using daily precipitation data,and projected population undershared socioeconomic pathways(SSPs).The IntensityeAreaeDuration method was applied to detect the extreme precipitation event by tracingthe rainstorm process,calculated based on five downscaled and bias-corrected Global Climate Model(GCM)outputs from Coupled ModelIntercomparison Project Phase 5(CMIP5)under four Representative Concentration Pathways(RCP2.6,RCP4.5,RCP6.0,and RCP8.5).Theexposure of the population is finally estimated by combing SSP1 with 1.5℃,SSP2 with 2.0℃,and SSP5 with 3.0℃warming levels.Resultsshow that warming over the Indus River Basin is projected to be higher than that of the global average.Both the extreme precipitation events andpopulation exposure are projected to increase with warming level.With regard to the reference period(1986e2005),the frequency,duration,andimpacted area of extreme precipitation are projected to increase by 13.2%,7.4%,and 1.6%annually under 1.5℃in the Indus River Basin,respectively.Whereas,an additional 0.5℃and 1.5℃warming can lead to further increase in the frequency of 16.6%,17.3%,as well as theduration of 8.6%,12%,and areal coverage of 2.1%,5.3%,respectively.The population exposure to extreme precipitation is projected to increaseby 72.4%,122.7%,and 87.6%,respectively,at SSP1 with 1.5℃,SSP2 with 2.0℃and SSP5 with 3.0℃warming levels compare to thereference period.The demographic change is responsible more for the tremendous increment of population exposure in the Indus River Basin.Ifthe population was held constant to the level of 2010,the increase of population exposure would be 4.4%,8.8%,and 17.6%,respectively,at1.5℃,2.0℃,and 3.0℃warming levels.Spatially,the prominent increment of population exposure is projected in the central and southwesternIndus River Basin.This study highlights that limiting the increase of temperature to 1.5℃can substantially reduce population exposure toextreme precipitation events in the Indus River Basin,compared to an additional warming.Simultaneously,urge paid to formulate policies onpopulation growth to reduce future exposure.