Projection Of Future Drought Changes In Arid Regions Of Asia In The Context Of Global Warming

Drought has become a major threat to local sustainable development in dryland Asia,one of the largest grassland ecosystems in the world.However,empirical or science-based evidences about the extent of drought changes and the future trends of these changes in dryland Asia are variable and incomplete.In this study,we first investigate the historical variations in drought conditions in dryland Asia,measured by drought intensity and arid area,using three widely used drought indices(i.e.,the Palmer Drought Severity Index(PDSI),the Standardized Precipitation Index(SPI),and the Standardized Precipitation Evapotranspiration Index(SPEI)).Then,we take advantage of Bayesian model averaging(BMA)to reproduce the future drought conditions under two representative concentration pathways(RCP2.6 and RCP4.5)from the Coupled Model Inter-comparison Project Phase 5(CMIP5)earth system models.The PDSI,SPI and SPEI illustrate that dryland Asia has experienced an overall drying trend and an expansion of arid areas over the last 100 years(1901-2016).Both temperature and precipitation are projected to increase under both 1.5? and 2.0? warming scenarios compared with the values from the reference period(1986-2005).The projected drought conditions in the 1.5? and 2.0? warming scenarios will worsen,especially across Kazakhstan.We found that the drought condition under 2.0? warming conditions will not be as severe as that under the 1.5? warming conditions due to the mitigating effect of the projected precipitation increase under RCP2.6 and RCP4.5.Meanwhile,we applied an ensemble of the 12 latest model simulations of the Coupled Model Intercomparison Project Phase 6(CMIP6)to assess future drought conditions until 2099 in Northwest China,as inferred from the PDSI.Future drought conditions were projected under three climate change scenarios through the combination of shared socioeconomic pathways(SSPs)and representative concentration pathways(RCPs),namely,SSP126(SSP1-RCP2.6,a green development pathway),SSP245(SSP2-RCP4.5,an intermediate development pathway),and SSP585(SSP5-RCP8.5,a high development pathway).For 2015?2099,drought severity showed no trend under SSP126,in contrast,for the SSP245 and SSP585 scenarios,a rapid increase during 2015-2099 was observed,especially under SSP585.We also found that the drought frequency in Northwest China under SSP585 was generally lower than that under SSP126 and SSP245,although the drought duration under SSP585 tended to be longer.These results call for short-term and long-term mitigation and adaption measurements to drought events in dryland Asia.