南水北调西线工程区降水特征分析

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

利用30个站的1965—2000年日降水资料,分析了南水北调西线工程区的降水气候特征、降水过程特征和降水极值特征.结果表明:该区多年平均降水量为520.5 mm,年降水量等值线呈东北-西南向分布,由西北向东南递增,半干旱区和湿润地区年降水量的分界线在该区沿玉树-清水河-大武-河南-合作-临洮一线分布;降水过程大部分大于5 d,降水集中在3 d左右,过程降水量可分为纬向类和斜向类两种,斜向类占大多数,其中斜向类又可分为西北-东南向、东北-西南向两种,以西北-东南向的发生较多.降水中心由西北向东南方向移动,或中心变动不大,但范围先加大后减小.在所有降水过程中,一日最大雨量出现在壤塘的频率最高,其次为若尔盖和临洮;3 d最大降水量最频繁发生在临洮,其次为壤塘和若尔盖.18次过程降水极值分布与多年的年降水量大值区相对应.1965年、1984年、1992年过程降水偏弱,1981年、1989年、1999年过程降水偏强.

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 - HenanHezuo- 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 diago-nal. The latter has a larger percentage, with northwest-southeast and northeastsouthwest 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 precipi- tation occurs mostly in Rangtang, following in Ruoergai and Lintao. The 3-day maximum precipitation occurs mostly in Lintao, following in Zoig6 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.