Temporal And Spatial Variation Of Precipitation On The Qinghai-tibetan Plateau And Its Impact Under Climate Change

The Tibetan Plateau(TP)is known as the "roof of the World" and the "third pole" of the earth.Being an important part of water cycle,precipitation over the TP not only affects the distribution of water resources in East Asia and South Asia,but also has a significant impact on the water cycle,permafrost evolution,desertification process,and ecological environment of the Plateau itself.However,due to the complexity of the terrain and the limitation of technical means,precipitation data from the ground observation stations cannot offer a wider observation range and a smaller space interval,and the accuracy of satellite data this area often needs to be further improved.Aiming at obtaining the precipitation data products with high accuracy and resolution and overcoming the limitations of the observational data of ground stations and the TRMM precipitation products,this paper adopts the variational method to integrate the two kinds of data.Based on the new precipitation product,researches on the change of precipitation distribution,and on the TP,studies on the distribution and variation of precipitation on the TP have been carried out.Further more,the effects of precipitation distribution and its change on glaciers and vegetation change under warming and wetting background are analyzed.In addition,the global effect of water vapor transport window over the plateau is discussed.The main conclusions are as follows:(1)A modified method of optimized interpolation variational correction method is introduced to obtain high resolution precipitation products over the Tibetan Plateau.With the optimizing interpolation variational correction method,the TRMM satellite precipitation variational products can be used not only as the objective supplements of the “blank area" of the TP precipitation observation stations,but also to improve the accuracy of TRMM precipitation products.The TRMM precipitation products can be applied to describing the high-resolution precipitation distribution characteristics,and to integrating the actual ground observation data.After correction,the product can describe the spatial and temporal distribution characteristics of precipitation over the TP in a more objective and refined manner.(2)The analysis of precipitation over the Qinghai-Tibet Plateau from 1998 to 2018 has been carried out by using the new TRMM precipitation products after optimized variational variation.It shows a gradually decrease from southeast to northwest over the TP.From the perspective of precipitation variation trend,precipitation in the southern edge of the Himalayan Mountains,the Yarlung Zangbo River and the southeast of the TP showed a downward trend,while precipitation in the area near the Qaidam Basin in the northeast of the Plateau showed a slow increase trend.(3)By using the multi-source data of meteorology over recent decades,we find that water vapor from the TP is driven by heat sources in the plateau,transporting upward and forming an anticyclone over the troposphere.The water vapor in the high level of the TP not only travels to the surrounding areas,but also forms a water vapor transport channel extending to the north and south poles.This confirms the window effect of the plateau on global water vapor transport,especially over remote regions such as the Arctic and Antarctic.(4)The correlation and influence analysis of temperature and precipitation changes and glacier retreat in TP shows that there are differences in glacier retreat in separate regions of the TP.The retreat of glaciers in the north-south is obviously related to the precipitation variability of the glaciers area.In other words,climate warming is the main cause of glacier retreat in the TP,and the change of precipitation recharge in the representative glacier area is also one of the key factors that can not be ignored in the influence of glacier retreat degree.(5)In recent 20 years,the enhancement of trans-equatorial warm and wet air flow from the Indian Ocean under the influence of the South Asian monsoon has brought some precipitation "recharge" to the glacial region of the northwestern TP,where the glacier retreat is weak.At the same time,the Himalaya-Southeast Tibet glacier area is affected by the East Asian seasonal warm and wet air flow from the western Pacific Ocean.However,with the weakening of warm and wet airflow under the control of East Asian monsoon,the precipitation in the summer half year in this region decreased,leading to the imbalance of precipitation "supply",which resulted in the significant retreat of glaciers in the southern margin of the TP under the background of global warming.Under global warming,the northwest TP is in the ascendingn branch of the vertical water driven thermally by the tropical Indian Ocean.The warm water vapor from the tropicalnocean climbs to the TP,forming a significant supply effect of precipitation in the northwestern glacier area,which makes the glacier retreat at a relatively low rate.Meanwhile,the southern and southeastern TP regions are in the descending branch of vapor transport with the declining trend in the lower troposphere,which lead to the shortage water supply aggravating the glacier loss in the southern and southeastern TP.(6)By comparing the changes of temperature and precipitation in the growing season of vegetation over the Tibetan Plateau,we draw a conclusion: Temperature is not the only determinant that can affect vegetation growth;a one-month lagging correlation effect is identified between precipitation and LAI variability distribution.The warming and wetting of the TP promotes the changes of the vegetation environment,but there are regional differences in the changes of the vegetation environment in the northern and southern parts of the TP.In addition to the main cause of temperature rise,these regional differences are correlated with the regional characteristics of spatial and temporal distribution of precipitation over the TP.The South Asian and East Asian monsoons,as the major driving factors of the warming and wetness of the TP,also influence the regional variation of the ecological environment of the TP through the inter-annual and inter-decadal changes of water vapor transport structure.