Analysis Of The Spatial And Temporal Distribution Characteristics Of Precipitation In The Pamirs From 1979 To 2018

On the western edge of the Tibetan Plateau,the Pamirs is a huge mountain junction of the Kunlun Mountains,the Karakoram Mountains,the Hindu Kush Mountains and the Tianshan Mountains,it covers an area of about 10,100 km2,with an average elevation of over 4,500 m.The Pamirs is the birthplace of many rivers,such as the Indus,Amu,Tarim,Yarqiang and Kashgar rivers.Atmospheric precipitation and the melting of glacial snow in the Pamirs provide over 50%of the runoff source for the surrounding rivers,which play a vital role in the water resources of Central Asia.Water resources in Central Asia are becoming more and more tense.How to well use the limited water resources in the Pamirs is an important prerequisite for having a full understanding of the spatial changes of atmospheric precipitation in the Pamirs.However,the current research on the atmospheric precipitation of the Pamirs is still lacking,and the research on the characteristics of temporal and spatial changes of precipitation,and its mechanism is also insufficient,mainly because the landform of the Pamirs is complex and the altitude is high.There is almost no precipitation observation data above 4000m altitude.and limited stations are located in the lower river valleys,the spatial distribution is very uneven,which leads to the lack of understanding of precipitation changes in the high altitude area of Pamirs.The current observation data alone cannot get the spatial distribution characteristics of precipitation in the Pamirs,which is very detrimental to the comprehensive understanding of atmospheric precipitation and its water resources in the Pamirs.To overcome the shortage of observational data,this thesis uses GPCC global land precipitation grid data,ERA5 reanalysis data,and WRF model simulations to analyze the spatial and temporal variation of precipitation in the Pamirsfrom 1979 to 2018.Explore the distribution characteristics of precipitation with altitude,discuss the spatial distribution of precipitation and its relationship with water vapor transport,and lay a scientific foundation for understanding the changes in precipitation and water resources in the Pamirs.The main conclusions of this paper are:(1)The average annual precipitation in the Pamirs from 1979 to 2018 increased at a trend of 1.3 mm/a,while the annual precipitation trend in the past 10 years reached 0.94mm/a.There is a significant difference in seasonal precipitation in the Pamirs.Spring(March to May)has the most precipitation,followed by winter,and the least in summer and autumn.In the past 40 years,precipitation in all four seasons has shown an increasing trend.The increase in winter precipitation has contributed the most to the increase in annual precipitation.(2)The spatial distribution of annual average precipitation in the Pamirs is extremely uneven.Under prevailing westerly winds,the west has more precipitation than,the east,and there are three precipitation centers in the plateau,located in the northwest,southwest and southern edge of the Pamirs.(3)The location of the anticyclonic circulation center near the Red Sea will affect the transmission of the westerly air to the east,resulting in a difference in the seasonal distribution of water vapor.The water vapor flux in the northern part of the Pamirs is greater than that in the south.The water vapor is mainly transmitted along the Mediterranean-Caspian-Pamirs(north branch)and Mediterranean-Pamirs(south branch).The northern branch mainly affects the northern part of the Pamirs,while the southern branch mainly affects the northern part of the Pamirs.(4)Topography is the major reason for the difference in the spatial distribution of water vapor.The foothills on the west side of the Pamirs intercepts the water vapor carried by the westerly wind,the largest precipitation occurs in the windward foothills on the west side of the Pamirs.The distribution of precipitation in the Pamirs is not a monotonous increasing trend with altitude.The maximum precipitation is mostly occurring in the peaks of 4km and 5km above sea level,followed by windward slopes with an altitude of 1-3km.Precipitation on the east side of the Pamirs is more prominent in summer than the other season,indicating that the water vapor brought by the westerly wind through the Tianshan Mountains can affect the east side of the Pamirs more than the transmission of the westerly wind from west to east.(5)The WRF model is used to simulate the spatial variation of precipitation with high resolution of 5km,taking the extreme high precipitation year(2016)of 40a and the extreme low precipitation year(2001)as examples.Combined with the discussion of water vapor transport,the strength of the westerly wind cause the abnormal precipitation,and that the westerly wind can also expand and enhance the influence range and capacity of the water vapor transmission path in the south branch.