中文摘要：

本文借助ArcGIS 9．2和Matlab 7．0数据软件平台，运用复值Morlet小波分析和数理统计方法对石羊河流域极端干旱事件在时空上的变化特征进行分析，结果表明：①石羊河流域的平均湿润指数自北向南逐渐增大，其湿润指数与年均降水和海拔高度具有显著正相关性（在0．01置信水平），而与年均蒸发具有显著负相关性（在0．05置信水平）。②在时间尺度上来说，极端干旱事件的频数具有19a、9a、6a、4a、15a的周期，可能是受南亚高压的准3年周期的影响；在空间尺度上来说，极端干旱事件频数与湿润指数的空间分布大体相似，略有不同是两者的最小值不同：即地表湿润指数最小值在民勤，而极端干旱事件发生频数最小值在武威。7-9月份发生极端干旱频数占年极端干旱总频数的60．62％。③年极端干旱总频数和7-9月份极端干旱总频数都呈略微上升趋势，且年极端干旱频数的线性倾向率较大，即将达到0．3／10a。通过Pettitt突变检验法对年极端干旱总频数和7-9月份极端干旱总频数进行检测，结果检验到突变点分别为2000年和1983年（在0．01置信水平）。

英文摘要：

With global warming, hot days and warm nights have significantly increased, but cold days and cold nights have decreased, and the frequency of extreme weather and climate events has significantly increased. Climate warming has four major challenges for our economy to face, of which the first challenge is the extreme weather events. The frequency of extreme weather events is getting bigger, with a tendency of getting stronger. Drought in global wanning becomes more prominent and sensitive, and is one of the key and hot issues in cli- mate change research. This paper analyzes the spatial and temporal characteristics of extreme drought events in Shiyang River Basin, combining ArcGIS 9.2 and Matlab 7.0 data software platform and using complex Morlet wavelet analysis and mathematical statistical theory. The results show that： （1） the average humidity index in- creases gradually from north to south in Shiyang Basin, and annual precipitation and altitude have significant positive correlations with the moisture index （0.01 confidence level）, while the annual evaporation has a signifi- cant negative correlation （0.05 confidence level）. （2） From the time point of view, the cycle with extreme drought is 19a, 9a, 6a, 4a and 15a, which may be affected by the South Asia High pressure with a three-year cy- cle. In spatial scale, the spatial distributions of the extreme drought frequency and surface moisture index are broadly similar, with slight difference, of which the lowest extreme drought frequency is in the Wuwei region, and the humid index in Minqin is the smallest in the study area. Furthermore, the extreme drought events occur mainly from July to September, and the extreme droughts frequency of this period accounts for 60.62% of the to- tal frequency throughout the year. （3） The annual and July-September extreme drought frequencies show a slight upward trend, and the linear trend of the annual frequency is obvious to reach about 0.3/10a. The sudden change of the annual and July-September of extreme