Anlysis on Extreme Precipitation Envent over the Northwest China in Flood Season
中国西北汛期极端降水事件分析

Based on the daily precipitation data of flood season(Mar to September) in 1960-2004 from 125 stations in Northwest China,we firstly determined the extreme precipitation threshold values for every station,then counted the extreme precipitation event frequency in flood season and analyzed their temporal and spatial characteristics.The results show that the spatial distribution of extreme precipitation event frequency in flood season is remarkably different from the distribution of precipitation,and the consistent anomaly distribution is the main spatial model of extreme precipitation event frequency in Northwest China.The spatial distribution of extreme precipitation event frequency in Northwest China can be divided into six regions: east of Qinghai-Xizang Plateau,south of Xinjiang,north of Xinjiang,east of Northwest China,Qinghai Plateau,and Hetao area.Seen from long-term changing trend,the extreme precipitation event frequency in flood season from 1960 to 2004 appeared no obvious changing trend in the east of Qinghai-Xizang Plateau,remarkable increasing trend in the north of Xinjiang,the south of Xinjiang,Qinghai Plateau,and Hetao area,but a clear decreasing trend in the east of Northwest China.The periods of 45-year and 13-year were relatively outstanding in variation of the extreme precipitation event frequency in Northwest China.