中文摘要：

利用中国西北地区138个观测站1961年-2007年逐日降水量资料,采用趋势分析、Mann-Kendall分析、小波分析等方法,分析了47年来西北地区大雨以上降水日数的时空分布特征及其变化规律。结果表明：西北地区大雨降水日数从东南向西北减少,祁连山和天山有两个相对多雨区。在季节分布上,冬季最少,夏季最多,秋季多于春季;大多数地方大雨降水日数有不显著增多趋势,显著区在天山地区,但西北东部略有减少趋势;全区大雨降水日数存在22年周期,除祁连山区1967年有突变现象,其余地方近47年未发生突变;以全区大雨降水总站次数序列分析,冬季较少,但20世纪90年代中期以来有所增多,春季不明显,夏季略有增多,秋季略有减少趋势;西北地区总体上降水日数为单峰型,7月为峰值,集中出现在5月-9月;西北地区日最大降水量12.8～203.3mm,从东南向西北减少,在陕西西南部的佛坪、陇中的临洮、青海北部的德令哈和天山的巴仑台各有一个高值中心。年最大日降水量普遍有增加趋势,除天山以外,大多数地方增加不显著

英文摘要：

Heavy rainfall has both advantages and disadvantages to northwestern China since it may form flood and mud-rock flow disasters;meanwhile,it can be beneficial to relieving agricultural drought and reservoir impoundment electricity generation.Studying heavy rainfall is therefore of great importance to improve our understanding of regional climate resources and their exploitation over northwestern China.With Mann-Kendall,trend analysis,and wavelet analysis,spatial distribution characteristics and the evolution of days with above heavy rainfall across northwestern China for 47 years were comprehensively analyzed based on daily data during the period 1961-2007 from 138 stations.Results show that days with above heavy rainfall decreased from the southeast to the northwest.The Qilianshan and Tianshan areas showed relatively high values.As for seasonal distribution,days with above heavy rainfall were least in winter and most in summer,with autumn being larger than spring.Days with above heavy rainfall for most places over this region exhibited slightly increasing trends,especially over the Tianshan areas.For the eastern part of the region,there existed slightly decreasing trends in the days with above heavy rainfall.In general,the days with above heavy rainfall had a 22-year interannual cycle.There was a remarkable mutation in 1967 over the Qilian mountainous areas.By sequence analysis,it was found that since the mid-1990s,days with above heavy rainfall in winter and summer increased to a certain degree,decreased in autumn,and remained fairly invariant in spring.Northwestern areas exhibited a single peak of days with above heavy rainfall as a whole,within the peak occurring in July and the majority of the days being concentrated between May and September,which accounted for 92% of that of a year.The maximum daily rainfall ranged between 12.8 mm and 203.3 mm over this region,decreasing from the southeast to the northwest,peaking around Foping in southwestern Shaanxi,Lintao in Gansu,Telingha and Tianshan’s Baluntai in no