关键词: 西北地区东部, 5~9月可利用降水, REOF分析, 空间分布模态及时间系数

Abstract: Using the observed temperature and precipitation data of 91 observation stations located in eastern part of northwest China during 1961 to 2009，the precipitation, evaporation and utilizable precipitation were calculated，applying the statistical methods such as EOF，REOF and so on，the spatiotemporal variation characteristic of utilizable precipitation in eastern part of northwest China was analyzed．The result shows as follows：（1）The mean annual precipitation in eastern part of northwest China was less than 350 mm，but the evaporation was up to 270 mm, only 13% of precipitation was utilized，moisture resource was scarce and its interannual variation was great in this region．（2）The spatiotemporal distribution of moisture resource in this region was extremely asymmetric，moisture resource reduced progressively from southeast part to northwest part as a whole．In south part of this region，utilizable precipitation was up to 30% to 50%，but over 90% precipitation was evaporated in north Ningxia，west Qinghai and most part of Shaanxi．In Gansu Corridor，99% precipitation was evaporated．Most moisture resource was in summer and least in winter．The precipitation,evaporation and utilizable precipitation during May to September was up to 82%，79% and 91% repectively in whole year，so the period from May to September was not only the main precipitation period，but also the concentration period of utilizable precipitation．（3）Precipitation played a decisive role in each component of moisture resource，little variation of precipitation could lead to big variation of utilizable precipitation，so it was the main reason that caused the dificient of utilizable precipitation resouce in the eastern part of northwest China．But the influences caused by temperature variation couldn’t be ignored．（4）The distribution of utilizable precipitation during May to September in eastern part of north-west China was abnormal with obvious regional distribution characteristic，by the EROF analysis during May to September in this region，the cumulative variance contribution rate of first 4 rotation load vectors was up to 53%，so there were usually 4 abnormal distribution modes，they are Longnan,Hedong,Plateau and Gansu Corridor distribution modes．（5）In recent 50 years，the utilizable precipitation reduced linearly in eastern part of northwest China and increased in western part，but the decreasing rate was bigger comparing with the increasing rate，it was in accord with the variation of precipitation in this region．

Key words: eastern part of northwest China, utilizable precipitation during May to September, REOF analysis, spatial distribution mode and temporal ratio