西北东部极端降水事件及异常旱涝季节变化倾向

利用西北地区东部100个气象观测站1960_2000年逐日降水资料,对降水、极端降水事件及异常旱涝区域面积的季节变化倾向进行了分析。结果表明:春、秋、冬季,虽然极端降水事件频次的变率小于降水距平百分率的变率,但两者的变化趋势一致,春、秋季呈上升趋势,冬季呈下降趋势,表明极端降水事件出现的多与少,基本决定了季节降水趋势的变化;夏季,暴雨出现的多与少不能完全决定夏季降水量的趋势,而大雨频次的变化趋势与降水距平百分率的变化趋势一致,略呈上升趋势。夏季降水异常偏少的区域面积呈减少趋势,表明干旱发生的区域面积缩小了;秋季降水异常偏少的区域面积从20世纪80年代中期开始明显的扩大,表明干旱发生的区域面积增大了;春、冬季,降水异常偏多、偏少的区域面积是对称变化的,即降水异常偏多的区域面积增多,则异常偏少的区域面积减少;反之亦然。

Trends of Seasonal Extreme Precipitation Events and Drought and Flood over the East of Northwest China

Using daily precipitation data of 100 meteorological stations from 1960 to 2000 we have analyzed the trend of seasonal precipitation,trend of extreme precipitation events and the area percentage with extreme drought and flood in the east of Northwest China.The results show that although the variability of extreme precipitation event frequency is smaller than that of the precipitation departure,there is a synchronous trend between them.They all increase in spring and autumn and decrease in winder,which indicates that the frequency of extreme precipitation events decides the trend of precipitation mainly.In summer,the frequency of extremely heavy precipitation events(>50 mm per day) can not decides the trend of summer precipitation completely.But there is a synchronously slightly increasing trend between frequency of heavy rain(>25 mm per day) and precipitation departure.Areas with much less than normal amount of precipitation in summer have been decreased,which indicates that areas occurred drought in the study region have been decreased.Whereas,areas of abnormal less precipitation in autumn have been expended significantly from middle of 1980s,which indicates that areas occurred drought in the study region have been increased.In spring and winter,abnormally more amount of precipitation scope expended while abnormally less amount of precipitation scope reduced,or vice versa.