Assessment Of Simulation Capability And Projection Of Drought Over China Based On CMIP6 Global Climate Models

Based on CN05.1 observation grid data and Coupled Model Intercomparison Project Phase 6(CMIP6)model simulation data,the study comprehensively evaluated the simulation capability of CMIP6 models for selfcalibrating Palmer Drought Severity Index(sc PDSI),temperature and precipitation in China,and projected the change characteristics of sc PDSI,temperature,precipitation,runoff and soil moisture under SSP1-2.6,SSP2-4.5 and SSP5-8.5 scenarios in China in the 21 st century,and analyzed the uncertainty of CMIP6 future projection and the causes of the drought changes in China in the 21 st century.The results show that the capability of CMIP6 models for temperature in China is the best,followed by precipitation,while its ability to simulate sc PDSI is weaker than the first two,but the multi-model ensemble of sc PDSI can effectively improve the simulation performance.The temporal trend of sc PDSI shows a slight increasing trend under SSP1-2.6 scenario(0.03/10 a)and a decreasing trend under SSP2-4.5 and SSP5-8.5 scenarios,of which the trend values are respectively-0.07/10 a and-0.11/10 a.The temperature in China in the 21 st century shows an increasing trend in both annual and four seasons,and the annual mean temperature increases by 2 ℃,3 ℃ and 6 ℃ under three emission scenarios at the end of the 21 st century,respectively.The spatial distribution pattern of temperature is rising trend over China,with the SSP5-8.5 scenario showing an apparently higher trend than the SSP1-2.6 and SSP2-4.5 scenarios.For precipitation,the annual average precipitation in China in the 21 st century is also rising,and the trend of SSP5-8.5 scenario(2.73 %/10 a)is apparently higher than that of SSP1-2.6 and SSP2-4.5 scenarios,of which the trend values are 1.55 %/10 a and 1.17 %/10 a,respectively.The temporal trends of four seasons are similar to the annual precipitation.Besides,the spatial distribution of annual precipitation in most regions of China is increasing,with a slight larger increasing trend in northwest China,Qinghai-Tibet Plateau and Inner Mongolia than other regions.The annual surface runoff shows increasing trends under SSP1-2.6 and SSP5-8.5 scenarios,the trend values of them are0.03 %/10 a and 5.03 %/10 a,respectively,while the SSP2-4.5 scenario shows a decreasing trend(-0.53 %/10 a).In terms of the spatial distribution,the most regions of China are increasing.The annual total runoff increases over time in the 21 st century,and the amplification of the high emission scenario is much larger than that of the low and medium emission scenarios.Top-10-cm soil moisture and total soil moisture show decreasing trends over time,and the decreasing amplitude increases as the emission scenarios become higher.The spatial distribution pattern is generally "high in the North and low in the South",the downtrend is most significant in the Qinghai-Tibet Plateau region,and the change range of surface soil moisture is bigger.The probability density curves of all variables in the 21 st century flatten under higher emission scenarios,the future changes become more dramatic.The summer Indian Ocean SST and North Atlantic Oscillation(NAO)are important factors affecting drought in China.When the Indian Ocean SST rises in summer,the Indian monsoon weakens and the water vapor transport into China decreases,which is favorable to the drought in Central and Southern China.Besides,when the North Atlantic Oscillation strengthens,the water vapor transport over the Caspian Sea and the Aral Sea is abnormally northward,which reduces the water vapor entering northern China and leads to the drought in the region.