Variation Characteristics of Precipitation Extremes in Beijing during 1981–2010

Daily precipitation data of 20 national stations in Beijing area during 1981–2010 are used to study the extreme precipitation exceeding relative thresholds(upper 90th, 95th, and 99th percentiles of precipitation for local sites and given time). The results show that the relative thresholds of 90th, 95th, and 99th percentiles have a similar spatial distribution. The distribution of extreme precipitation days shows a significant difference from the precipitation amount and relative threshold calculated as the upper 95th percentile. The extreme precipitation amount can account for 30%–37% of the total precipitation amount. The distribution of extreme precipitation intensity is consistent with the extreme precipitation threshold. In the recent 30 years, the extreme precipitation amount, days, and intensity of most stations in Beijing area have shown apparent decreasing trends. In Shangdianzi, Huairou, Pingu, and Guanxiangtai stations, the decreasing trend of extreme precipitation amount is obvious, reaching a value of 40 mm(10 a)–1. In Shunyi, Haidian, Guanxiangtai, Daxing, and Shangdianzi stations, the decreasing trend of extreme precipitation intensities is more pronounced, with precipitation intensity being as low as 4 mm d–1(10 a) –1. The distribution trend of extreme precipitation amount is positively related to the precipitation frequency and that of extreme precipitation intensity is inconsistent with the precipitation amount,frequency, and patterns of distribution.