A Study On The Spatial-Temporal Distributions Of Areal Precipitation And Water Vapor Over Xinjiang

Accounting for about sixth of Chinese land,Xinjiang Uiger Autonomous Region is a typical arid and semi-arid area,water resources distribute extremely asymmetrically and have been a vital factor to restrict the economic and social developments and ecological protections in this region.This paper analyses annual and seasonal distribution and change characteristics of areal precipitation,explores water vapor transportations in high altitude and Atmospheric Precipitable Water(APW) in Xinjiang by using 144 meteorological and hydrological stations during 1961～2005,daily NCEP/NCAR reanalysis data during 1961～2000 and 1km×1km DEM data.The methodologies include EOF,multi-regression analysis,maximum entropy analysis and Geographic Information System.The results show that:in Xinjiang,annual mean areal precipitation is around 2724.6×10~8ton,annual mean precipitation is 165.5mm.As spatial distributions,there is the most areal precipitation in Tianshan mountainous region,accounting for about 40.4%out of total Xinjiang areal precipitation,its annual mean precipitation is 409.1mm;the second high value is in northern Xinjiang,the percentage of areal precipitation in this area is about 34.3%and the annual mean precipitation is 277.3mm;Southern Xinjiang has the least areal precipitation which is some 25.3%out of total and its annual mean precipitation is only 66.2mm.To seasonal distributions, summer has the most areal precipitation which is about 54.4%out of annual total.The areal precipitation in other three seasons respectively are:spring is 23.6%,autumn is 16.5%and winter is only 5.5%.Over the past 45 years of 1961～2005,the interannual variation range of areal precipitation in Xinjiang was relatively larger and presented an increasing trend,especially from 1987,precipitation increased significantly.Areal precipitation in Xinjiang also showed a about 3-year periods swing.The annual mean inflow water vapor to Xinjiang in high altitude is about 26114.8×10~8ton,annual mean outflow is around 469.1×10~8ton.Due to the special terrain of three sides mountains in north,west and south,the annual and seasonal maximum water vapor transportations are all in medium troposphere,with less but close quantity of water vapor transferring in low and high tropospheres.The most water vapor coming and out Xinjiang area occurs in summer,accounting for about 38%out of annual total;In spring and autumn,the water vapor quantities are almost same,about 23%—25%;In winter,it's the least.During the 40 years(1961～2000),there were decrease trends in inflows and outflows of annual,spring and autumn means with very near variation rates.There were no obvious changes in water vapor in and out of Xinjiang after 1976,therefore the net budget of water vapor in high altitude above Xinjiang kept no much change.The distribution of annual mean APW in Xinjiang presents as higher values in Tarim Basin and Zhunger Basin and lower values in high elevation areas such as Altai mountains,Tianshan mountains and Kunlun mountains.The maximum APW occurs in summer,but compares with east monsoon areas in the same latitude.In spring and autumn,the APWs are relatively less compared with in summer and in winter the APW is least.Except APW in summer,APWs in other three seasons are almost same as the east monsoon areas in the same latitude.The APW in summer is less than 25 mm which is the least limit value of monsoon areas.This means that Xinjiang is not affected by monsoon.The geographic distribution of APW is adverse with that of precipitation,videlicet,higher(lower)APW values corresponding to lower(higher) precipitation values.With the effects of westerly winds,the APW mode presents as an uniform change within Xinjiang area and has a stable distribution.It is very different from Xinjiang rainfall mode which changes a lot spatially.As mentioned above,there is no obvious change during 1961～2000,this indicates that APW is not a dominant factor determining precipitation,it is the result of dynamic condition,water vapor convergence and other causes.The results also show strong relationships among the changes of runoffs of Kidu River,Aksu River and areal precipitation,0℃height and temperature.These close relationships implie that climate change was the main cause which led to stable runoff increases of these rivers from the medium 1980s.In conclusion,by using a lot of new data and designing new interpolating scheme with considering effect of elevation on preicpitation spatial interpolation,we got some new results in Xinjiang such as annual mean areal precipitation,the interannual variation of areal precipitation presented an increasing trend during 1961～2005,the budget of annual mean water vapor in high altitude spatio-temporal distribution of annual mean APW and areal precipitations in some main river basens.