Abstract: 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 warming becomes more prominent and sensitive, and is one of the key and hot issues in climate 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 increases 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 significant 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 cycle. 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 total 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 droughts frequency can be detected by the Pettitt mutation test, which occurred respectively in 2000 and 1983 (0.01 confidence level).

Key words: extreme drought, humid index, Shiyang River Basin, spatial and temporal characteristics