Change of Annual Precipitation over Qinghai-Xizang Plateau and Sub-regions in Recent 34 Years

The authors have statistically analyzed the daily precipitation data from 1971 to 2004 of 82 meteorological stations on Qinghai-Xizang Plateau,based on which the climatic subregions have been got by using the REOF method.The change trend of precipitation for each subregion has been studied.Seen from the whole region,the Qinghai-Xizang Plateau situates in the Monsoon rainfall region,and has obvious local characters in the effect of East-Asia Monsoon,India Monsoon,Plateau Monsoon and Westerly system.On the whole,the precipitation on the plateau has an increasing trend in the past 34 years,with slight variation from 1970s to early 1990s and obviously increasing since then,especially in the recent 3 years.Summer rainfall completely determines the precipitation of arid regions in the plateau,so the precipitation has larger relative variability.Seen from sub-regions,the precipitation increased most remarkably in the south parts of Tibet and Sichuan,with a rate of 54.5 mm per ten years,the following are Qaidam Basin,Qinghai Lake,and Hexi Corridor.Whereas,the precipitation decreased in the east of Qinghai,the source region of the three large rivers,the Qilian Mountains,and the northwest of Sichuan.Geographically,precipitation decreased in the high altitude region and increased in the low altitude region.