Abstract: Yearly total precipitation has been continuously decreasing since the 1990s, accompanying with an acute problem of extremely heavy precipitation and drought. The daily precipitation data at 60 weather stations in the circum-Bohai Sea region from 1961 to 2007 were used to analyze the spatial distribution and temporal changes of the rainfall, intensity and frequency of extremely heavy precipitation, wherein the threshold of extremely heavy precipitation was determined by the percentile method. The results show that the extremely heavy precipitation of high intensity and frequency occurred where the corresponding annual rainfall was high, indicating that the rainfall of extremely heavy precipitation dominated the annual rainfall. Extremely heavy precipitation days showed a declining trend, especially in the central part of the Beijing-Tianjin-Hebei area. Extremely heavy precipitation frequently occurred from middle July to middle August, with the top frequency in late July. Over the last 10 years the seasonal distribution of extreme precipitation was temporally relatively disperse and the extremely heavy precipitation with more than 25 station days occurred in a pentad was scarce. In contrast, extremely heavy precipitation with an interval of more than 30 d increased significantly in recent years.

Key words: extreme heavy precipitation, frequency, intensity, circum-Bohai sea region