中文摘要：

为了揭示西北地区暴雨的时空演变特征，利用该地区109个站44年（1961—2004年）的日降水资料，采用小波分析等方法研究了该地区暴雨的气候变化。研究指出，西北地区平均每年有40站次的暴雨；暴雨频次最少的地方在中西部，最多的地方在东部；4—11月都可能出现暴雨，其中6—9月占93．1％。暴雨开始和结束的时间年际差异较大，最早可发生在4月初，最迟到7月中旬发生；最早8月初结束，最迟11月中旬结束。区域性暴雨平均每年发生4．7场次，主要发生在6—9月；第一场区域性暴雨平均日期为7月2日，最早出现在4月初，最迟在9月下旬；最后一场区域性暴雨平均日期为8月31日，最早结束于6月中旬，最迟结束于10月中旬。

英文摘要：

In order to get the character of spatiotemporal evolvement of rainstorm in Northwest China, The daily rainfall at 109 stations in the Northwest China during 44 years from 1961 to 2004 was analyzed with wavelet theory. Results show that there are 40 times of rainstorm at all stations every year on an average in the Northwest. The stations where the rainstorm occurs less in frequency mainly concentrated in west-central places in the Northwest. The stations with more rainstorm frequency located in east of Northwest. The rainstorm maybe is in April-November, and mainly is in July-September, which can reach 93.1% of the whole year. The date of the start and end of rainstorm is obvious different in year by year. The first rainstorm can happen at the beginning of April earliest, and at the mid-July latest; the last rainstorm can occur at the beginning of August earliest, and in mid-November latest. Average of the regional rainstorm is 4.7 times in Northwest China, the regional rainstorm happens mainly in June to Septamber. The average date of the first regional rainstorm is July 2. The first regional rainstorm can happen at the beginning of April earliest, and in the last ten days of September latest; the average date of the last regional rainstorm is August 31, the last regional rainstorm can occur in mid-June earliest and in mid-October latest.