Temporal And Spatial Variation Of Precipitation In Southeastern Tibet From 1980 To 2018 And Its Projection

The Southeastern Tibetan Plateau(SETP)is one of the glacier centers in the Tibetan Plateau and an important water supply area for the Brahmaputra River.Over the past several decades,the temperature has risen,precipitation has fallen,and glaciers have shown an accelerated retreat.However,the observational data in SETP is limited,and it is impossible to reveal the spatial distribution of precipitation and its variation with altitude,and the impact of glacier changes on precipitation is unclear.Therefore,reanalysis of data and numerical simulation is an important method to make up for the lack of observational data and to fully understand the temporal and spatial distribution of precipitation in SETP.Based on JRA-55,ERAS reanalysis data and the sixth Coupled Model Inter comparison Project(CMIP6)data,this paper conducts a comprehensive analysis of precipitation changes in SETP from 1980 to 2100.This paper uses the Weather Research and Forecasting(WRF)Model to simulate high-resolution of precipitation in SETP in 2017,revealing the characteristics of water vapor flux,precipitation,and the changing of precipitation with altitude in SETP.In addition,we design a sensitivity test on glacier extinction to explore the impact of glacier extinction on local precipitation in SETP.The main conclusions of the paper are as follows:(1)The SETP was the area with the largest precipitation in the Tibetan Plateau from 1980 to 2018,and it was also the area with the fastest decrease in precipitation,with a downward trend of 12mm/10a.In the past 40 years,the temperature has fluctuated at a trend of 0.18?/10a,and the increase in temperature in winter is significantly higher than that in summer.(2)The WRF model can more accurately simulate the precipitation process in SETP.Compared with the GPM data with resolution of about 10km,the WRF simulation with finer resolution of 3km shows more details of precipitation variation with terrain.The highest precipitation mainly concentrates in the trumpet of the Brahmaputra River with altitude below 3000m in each seasons.Summer precipitation is the largest and winter precipitation is the smallest.The maximum precipitation is at an altitude of 3000m.Below the altitude of 3000m,the precipitation shows an increasing trend with the increase of the altitude,while in the interval of 3000-5400m,the precipitation generally decreases with the increase of the altitude.(3)The difference between the control and the sensitivity tests reflect the glacier can impact the regional precipitation in the SETP.The glaciers could have inhibited the northward warmer Indian monsoon flow by the downward glacier wind.While in the absence of glaciers,as the cooling effect of glacier disappears,the original glacier area becomes a heating source and the downhill glacial wind turns to uphill wind,which strengthens the transportation of warm moist air to highland and then cause more than 20-50%precipitation in SETP.As the glacier disappearance,the south meridional surface wind speed will increases(decreases)in the south(north)slope of SETP.While the total column water vapor content will increase dramatically in the original glacier region,indicating glaciers cause the atmosphere over the glacier surface to be drier and decrease the northward surface wind.Strongly changes of water vapor flux mainly occur in the boundary layer with depth of about 1500m.In the absence of glaciers,vertical wind would increase over the original glacier area.We conclude that glacier loss expected in the next decades could substantially impact the precipitation pattern in SETP,thus highlighting another mechanism by which human-caused climate change could change future water resource of the Brahmaputra River.(4)The CMIP6 multi-model ensemble average simulation results show that from 2015 to 2100,the annual average precipitation in SETP showed an upward trend under the four scenarios of SSP1-2.6,SSP2-4.5,SSP3-7.0 and SSP5-8.5.Before the middle of the 21st century,the precipitation increase rate was relatively consistent and relatively small.By the end of the 21st century,there were obvious differences in the increase in precipitation under the four scenarios.From 2015 to 2100,the annual precipitation trends in SETP under the four scenarios were 10.2mm/10a,11.6 mm/10a,66.2mm/10a,and 96.mm/10a.In general,the annual precipitation increase in the future will show a spatial pattern of rapid south and slow north in SETP.Under the four scenarios,as the radiative forcing increases,the rate of precipitation increase gradually increases.