The Interdecadal Variability of Summer Precipitation over North China

Based on the daily precipitation data from 740 stations and NCEP/NCAR reanalysis daily datasets, the interdecadal variability and their causes for summer rainfall over North China are analyzed by means of composite analysis method.Interdecadal variability of rain belt is found closely related with the decrease of rainfall over North China after 1978. Meanwhile, the rain belt over eastern China also has a significant interdecadal variability in summer. In wet period of summer over North China, there is a broader area with smaller amount of precipitation between the northern and southern rain belt in eastern China. But in dry period of summer, the area becomes smaller. In wet period, the rain belt over North China can extend westward to 115°E at most time and nearly reaches the west boundary of North China. However, in dry period, the precipitation amount is much smaller. And the rain belt can hardly maintain to the west of 115°E not to mention 110°E, so the stretch of westward of rain belt over North China is not obvious.Interdecadal variability of atmospheric circulation and East Asia summer monsoon are the direct cause of interdecadal variability of rain belt over North China in summer. In wet period, anomalous southerlies from the sea develop into convergence with upward motion under the influence of the terrain, and the anomaly high pressure over the Bohai Bay urges the rain belt over North China to extend westward. However, in dry period, the anomalous northerlies develop into divergence and anomalous downward motion, which are not favorable for the westward extension of rain belt over North China.