中文摘要：

利用中国气象局整编的1960-2009年西南地区108站逐日气温、降水等资料,计算年、月地表湿润指数,并进行标准化,统计极端干旱发生频率,对年际、年代际、季风期和非季风期的极端干旱变化特征进行分析,得出结论：（1）整体上,四川盆地西南部、横断山区南端、广西南部沿海和贵州北部是近50年来年极端干旱发生频率明显增加的地区;年代际变化上,20世纪60-80年代极端干旱呈逐渐减少趋势,高发区交替出现在东南—西北—东,90年代下降明显,整个地区都转湿,进入21世纪后,极端干旱距平呈现正距平,且增幅较大,区域间差异却显著减小。（2）季风期与非季风期的极端干旱变化有很大差异,季风期极端干旱频率在不断增加,多发生在四川盆地周边海拔较高的山区、广西大部和＂帚形山脉＂地带,海拔对季风期极端干旱发生频率有一定影响;非季风期缓慢下降,整体偏湿。（3）通过滑动t检验和小波分析发现,季风期西南极端干旱在2003年发生突变,非季风期在1989年突变,年极端干旱发生频率是季风期和非季风期的突变叠加的结果;年极端干旱存在准5年和准12年的周期变化。

英文摘要：

Based on the daily data of temperature and precipitation of 108 meteorological stations in Southwest China from 1960 to 2009,we calculated the surface humid indexes of months and years,as well as the extreme drought frequency.According to the data,the temporal and spatial characteristics of the extreme drought frequency in inter-annual,inter-decadal,summer monsoon and winter monsoon has been analyzed.The results are indicated as follows：（1） In general,the southwest of Sichuan Basin,the southern part of Hengduan Mountains,southern coast of Guangxi and north of Guizhou are the areas in which the extreme drought frequency has significantly increased in the past 50 years.For the decadal change,from the 1960s to the 1980s the extreme drought frequency has presented a decreasing trend,and the high frequency area appeared alternately in the southeast-northwest-east of Southwest China;the 1990s is the most wettest decade and it is wet over the whole area.In the 2000s,the extreme drought frequency rises quickly,but the regional differences reduce.（2） In summer monsoon,the extreme drought frequency is growing,which generally happens in the high mountains around the Sichuan Basin,most parts of Guangxi and ＂the broom-shaped mountains＂.It is obvious that the altitude has impacts on the extreme drought frequency of summer monsoon;in winter monsoon,the area is relatively wet and the extreme drought frequency is decreasing.（3） In summer monsoon,the abrupt change happened in 2003,while the abrupt change of winter monsoon happened in 1989,and the joint abrupt changes in different periods lead to the extreme drought frequency variation.The departure sequence vibration of annual extreme drought frequency is quasi 5 years and quasi 12 years.