Water Cycle Change Of Drylands And Its Response To Climate Warming

The water cycle is an important process to maintain the dynamic balance of global water resources.Under the background of global warming,the water cycle has accelerated and the total amount and spatial and temporal distribution of water resources have changed significantly.The arid and semi-arid regions(hereinafter referred to as drylands)in China account for about 52% of the country's land area,where the ecological environment is fragile and land desertification is serious,which is an important ecological security barrier in China.This article analyzed the characteristics of dry and wet climate changes in dryland of China from 1980 to 2019 based on atmosphere-surface water budget and water cycle processes(precipitation,evapotranspiration,runoff,soil moisture,precipitable water vapor and divergence of moisture flux),quantitatively estimated the water budget in dryland of China.On this basis,the interdecadal variation characteristics of summer precipitation in drylands of China from 1960 to 2019 and the formation mechanism of dry and wet changes in drylands of China were studied.Further extending the study area to the global,the response of water cycle over drylands to a warming future for 2021-2100 is investigated using the Coupled Model Intercomparison Project Phase 6(CMIP6)models.The results show that:(1)The MERRA2 data set was selected to establish the atmosphere-surface water balance equation for the drylands of China by comparing various observations and reanalysis data.The total amount of precipitation,evapotranspiration and runoff in the drylands of China during1980-2019 basically met the surface water balance,which was about 0.981,0.936 and 0.046 trillion tons,respectively.In terms of spatial distribution,precipitation,evapotranspiration,runoff and surface soil moisture showed a significant increasing trend in southeastern Gansu,the Loop Plain and northern Xinjiang,and a decreasing trend in parts of the Hami Basin and northern Inner Mongolia,but an overall increasing trend.Over the past 40 years,precipitation,evapotranspiration,runoff and topsoil moisture in our drylands have increased by 0.21,0.17,0.02 and 0.05 trillion tons,respectively.In addition,Precipitation minus evapotranspiration(P-E)and summer precipitation in drylands of China show a clear trend of increasing in northwest and decreasing in north China(2)By the 105°E boundary,the summer precipitation in the drylands of China shows an opposite interdecadal variation characterized between the wet west and dry east.From the physical mechanism,the interdecadal phase transition of the North Atlantic SST longitudinal gradient excites the latitudinal Rossby wave train causing the meridional movement of the subtropical westerly rapids,which causes the anomalous upward(downward)motion in the northwest dryland of China(north China dryland),which is favorable to the low altitude convergence(divergence)and high altitude divergence(convergence),and the cloudiness and precipitation increase(decrease),making the northwest dryland wetter and the north China dryland drier.(3)The trend of dry season becoming dry and wet season becoming wet is expected to exist in the drylands of the southern hemisphere in 2021-2100,while the drylands of the northern hemisphere becomes dry in the wet season and does not change much in the dry season.For the global drylands,annual precipitation,evapotranspiration,and runoff will increase by about 6.71 mm/K,5.46 mm/K,and2.48 mm/K,respectively.soil moisture(-0.64 mm/K)tends to decrease,and thermodynamic effects tend to enhance water vapor dispersion in the drylands,favoring a decrease in P-E,which increases by only 0.05 mm/K.Therefore,with global warming,the global drylands will continue to become drier.