Based on climate data in Changsha from 1954 to 2010, the potential evapotranspiration and humid index were calculated,and the change laws of surface dry and wet conditions were analyzed, as indicated by the results, during the pas! 57 years, the humid index of Changsha increased slightly, but after |he wet season in 1990s, typical drought appeared in 2007, which was directly influenced by the abnormal change of precipitation and average temperature. It was found out during the process of extreme value study of intra-seasonal variability that the appearance of annual precipitation anomaly extreme value was consistent with the extreme value of humid index in spring, autumn and winter,the extreme value of annual potential evapotrsnspiration anomaly was in consistent with that of humid index, the spring humid index declined obviously m Changsha, summer and autumn draught produced severe impact on agncultural production.%根据1954 ～2010年长沙市气候资料,计算潜在蒸散量和湿润指数,分析长沙市地表干湿状况变化规律,结果表明:57年来,长沙市年湿润指数总体略有增加,但自20世纪90年代的丰水期结束后,进入21世纪以采出现了典型干旱年——2007年,该年份的出现与降水量和平均气温的异常变化有直接关系.在分季节分析极值过程中发现,年降水量距平极值与春秋冬季湿润指数极值出现时间吻合,年潜在蒸散量距平极值与夏季湿润指数极值出现时间吻合,长沙市春季湿润指数下降明显,伏秋连旱对农业生产影响严重.
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