利用西北五省(区)137个测站1961-2000年历年月降水量资料,采用EOF、REOF、小波分析对西北地区年降水量的时空分布、演变规律及各异常区的周期特征进行了诊断分析。结果表明:(1)西北区降水受大尺度天气系统影响,第一特征向量反映了全区一致的多雨或少雨,但也存在东西和南北的差异。(2)西北区年降水空间异常可分为6个气候区(异常型),即高原东北区、北疆区、青海东部区、西北东部区、南疆区、河西走廊区。(3)近40年中除高原东北区及西北东部区降水呈下降趋势外,其余各区呈上升趋势。(4)各异常区降水存在10年以上较长周期和3~4年短周期振荡,但其显著周期及其年代变化差异较大。

On the basis of the monthly precipitation data from 137 stations in Northwest China(NWC) for the period of 1961_2000, the temporal-spatial distributions and the evolution rule of annual precipitation in NWC have been studied using the methods of EOF, ROEF and wavelet analyses.The results are as follows: (1) The annual precipitation in NWC is affected by the large-scale weather systems.When the first eigenvector is positive value, the whole NWC will be rainy, and vice versa, but there are the rainfall anomaly differences between in the east and west, and in the south and in the over NWC.(2) The precipitation abnormal area can be divided into six subregions: Northeast Qinghai-Xizang Plateau, Northern Xingjiang, Eastern Qinghai, Eastern part of NWC(ENWC), Southern Xingjiang and Gansu Corridor.(3) The precipitation in each region changes with time, in recent 40 years, the precipitation in Northeast Qinghai-Xizang Plateauand ENWC are decreasing and those over the other subregions are increasing.(4) The precipitation in each subregion has a long-and-short periodic oscillations, but their main periodic and annual change laws are different from each other.