Characteristics of Temporal and Spatial Variation of Precipitation,Evaporation and Difference between Precipitation and Evaporation in North China

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.