近45a来中国西北汛期降水极值的变化分析

本文利用中国西北五省(区)1960-2004年125个台站汛期(5-9月)逐日降水资料,首先定义了不同台站的极端降水阈值,然后统计出了不同台站近45a来逐年汛期发生极端降水的频次、干日数、极端干期长度、湿日数及极端湿期长度,并对它们的长期变化趋势作了分析,结果表明:近45a来西北西部汛期极端降水发生频次、湿日数和极端湿期长度表现出增多和增长趋势,干日数和极端干期长度表现出减少和变短趋势;西北东部汛期极端降水发生频次、湿日数和极端湿期长度表现出减少和变短趋势,干日数和极端干期长度表现出增多和变长趋势;从整个西北来说,近45a来极端降水发生频次和湿日数表现出了增多趋势,极端干期长度表现为变短趋势,而干日数同极端湿期长度表现出周期波动状变化,另外干日数同极端湿期长度的变化趋势恰恰相反,而湿日数却与极端干期长度的变化趋势恰恰相反;自上世纪80年代以来降水极值变率较过去有所变大。

Analysis on Change of Precipitation Extreme Values in Flood Season over Northwest China in Recent 45 Years

Using the day-by-day precipitation data of 125 stations in northwest China in flood season(5-9month) during 1960-2004,this research definited extreme precipitation boundary for different stations at first,then counted up year by year frequency of extreme precipitation,drought days,extreme drought spell length,moist days and extreme moist spell length in flood season and analyzed their change tendency.The results showed the frequency of extreme precipitation,moist days and extreme moist spell length displayed increasing trend,drought days and extreme drought spell length displayed decreasing trend in recent 45a over west of northwest China;But in east of northwest China extreme precipitation frequency,moist days and extreme moist spell length displayed decreasing trend,drought days and extreme drought spell length displayed increasing trend;From whole northwest China,frequency of extreme precipitation and moist days displayed increasing trend in recent 45a,extreme drought spell display decreasing trend,but drought days and extreme moist days spell displayed period change,in addition tendency of drought days and extreme moist spell length were reverse,the tendency of moist days and extreme drought spell are also reverse;since 1980s the variability of precipitation extreme values were bigger than that of before.