中文摘要：

根据我国西北地区东部59个气象台站近50 a（1965-2014年）的逐日降水资料,将降水划分为小雨、中雨和大雨3个等级,分析了该地区夏季不同等级降水的降水量、降水日数和降水强度的空间分布特征,并讨论了不同等级降水量及降水日数与夏季总降水量的关系及其在典型旱涝年的空间分布差异。结果表明：（1）西北地区东部夏季降水日以小雨为主,约占总降水日数的81%;但在夏季总降水量中,小雨、中雨和大雨降水量相当,各约占1/3。（2）该地区夏季不同等级降水量、降水日数和降水强度的空间分布不均,但均大致呈现出由南向北递减的空间分布特征。（3）该地区夏季总降水量与中雨日和大雨日的相关关系显著,表明中雨以上量级降水日数的变化可基本反映夏季降水量的变化。（4）西北地区东部典型涝（旱）年,降水量的偏多（少）主要是由于中雨以上等级降水日数偏多（少）引起的中雨量和大雨量偏多（少）所致。

英文摘要：

Located in arid and semi-arid area,the eastern part of northwest China has scarce precipitation and is easily influenced by drought and flood. Based on the daily precipitation data collected from 59 stations in the eastern part of Northwest China during the recent 50 years（1965-2014）,the precipitation intensity can be classified into three levels：light rain（0.1-9.9 mm per day）;moderate rain（10.0-24.9 mm per day）;heavy rain（≥25.0 mm per day）. From the perspective of climatology,we analyze the spatial patterns of the three-level precipitation amounts,precipitation days,and precipitation intensity during summers of the 50 years in the areas,and we discuss their relations and the spatial pattern differences of typical drought and flood years through partial correlation coefficient calculation and composite analysis. Results show as follows：（1）The light rain occurred most frequently and its precipitation days accounted for 81% of total summer precipitation days,the moderate rain took the second place with 14%,and the heavy rain ranked the third（5%）. However,the precipitation amounts of light,moderate and heavy rain were roughly equal and each of them contributed about one third of total precipitation amount in summer.（2）The spatial distribution of amount,days and intensity for different grades of precipitation in the east of northwest China were uneven and decreased from south to north in varying degrees. The similarity coefficients of total precipitation amount to graded precipitation amount,days and intensity were more than 0.88.（3）The partial correlation coefficients of summer precipitation amount to moderate and heavy precipitation days were higher than 0.75 and reached the significant level. It showed that changes of moderate and heavy precipitation days could roughly reflect change of total precipitation amount in summer.（4）In flood（drought）years,graded precipitation amounts and days were more（less）than normal. With the rising level of precipitation,the percentag