The Precipitation Characteristics in the South to North Water Transfer Area of West China

The climatic characteristics of precipitation and the maximum precipitation in the west course of the South to North Water Transfer were analyzed using the daily precipitation data of thirty meteorological stations from 1965 to 2000.It is revealed that the mean annual precipitation is 520.5 mm.The contour lines of the mean annual precipitation run from northeast to southwest.The diversion from the semi-arid region to humid region runs along Yushu-Qingshuihe-Dawu-Henan-Hezuo-Lintao.Precipitation processes are almost longer than five days;most of them are in three days.According to the shape of precipitation,the precipitation process could be classified as two categories.One is latitudinal,and the other is diagonal.The latter has a larger percentage,with northwest-southeast and northeast-southwest shapes.The center of precipitation often moved from northwest to southeast.Sometimes the center moved a little,but the rain area is large and then gradually shrinking.The 1-day maximum precipitation occurs mostly in Rangtang,following in Ruoergai and Lintao.The 3-day maximum precipitation occurs mostly in Lintao,following in Zoige and Rangtang.The extreme values of the 18 precipitation processes are distributed similarly to the extreme values of mean annual precipitation.For the eight high water years,the precipitation processes in 1984 and 1992 were weaker and those in 1981,1989 and 1999 were stronger.