中文摘要：

利用华北地区1951-2000年80个观测台站的降水、气温的逐日观测资料分析京津唐地区、华北西部、华北中南部和胶东半岛地区降水、蒸发和降水蒸发差在1951～1965年、1966-1976年和1977-2000年3个时期年代际变化特征。京津唐地区和华北西部地区夏季降水和降水蒸发差从1977年开始减少得比较明显；而胶东地区和华北中南部地区从1965年开始减少，1977年之后减少的更加严重，但4个区域5、6月的降水和降水蒸发差却出现明显的增加。分析还指出，胶东地区和京津唐地区可利用水资源量减少最多。另外还利用欧洲中心（ECMWF）1958-2000年的700hPa风场资料分析了华北地区夏季降水异常的可能成因，分析结果表明：东亚夏季风在1977年之后明显减弱，造成我国华北地区夏季降水偏少。

英文摘要：

The characteristics of temporal and spatial variation of precipitation, evaporation and difference between precipitation and evaporation in four regions of North China are analyzed by using the daily observed precipitation and temperature data at 80 observational stations in North China during 1951-2000. The analyzed results show that the summer rainfall and difference between precipitation and evaporation decreased after 1977 in the regions of Jingjintang and the western part of North China, but the summer rainfall and difference between precipitation and evaporation decreased after 1965 in the regions of Jiaodong and the middle and southern part of North China, however, the precipitation of May and June increased in the four regions of North China. The analyzed results also show the water resource decreased most seriously in Jiaodong and Jingjintang regions of North China. In order to explain the cause of the interdecadal variability of summer rainfall in North China, the interdecadal variability of the East Asian summer monsoon are analyzed by using the monthly mean wind field at 700 hPa of ERA-40 data set from ECMWF. The analyzed results show that there was an obvious northerly wind anomaly distribution over North China after 1977, which caused below normal of rainfall in summer in this region.