关键词: 西北地区东部, 极端降水事件, 异常旱涝, 变化倾向

Abstract: Using daily precipitation data of 100 meteorological stations from 1960 to 2000 we have analyzed the trend of seasonal precipitation, trend of extreme precipitation events and the area percentage with extreme drought and flood in the east of Northwest China. The results show that although the variability of extreme precipitation event frequency is smaller than that of the precipitation departure, there is a synchronous trend between them. They all increase in spring and autumn and decrease in winder, which indicates that the frequency of extreme precipitation events decides the trend of precipitation mainly. In summer, the frequency of extremely heavy precipitation events (>50 mm per day) can not decides the trend of summer precipitation completely. But there is a synchronously slightly increasing trend between frequency of heavy rain (>25 mm per day) and precipitation departure. Areas with much less than normal amount of precipitation in summer have been decreased, which indicates that areas occurred drought in the study region have been decreased. Whereas, areas of abnormal less precipitation in autumn have been expended significantly from middle of 1980s, which indicates that areas occurred drought in the study region have been increased. In spring and winter, abnormally more amount of precipitation scope expended while abnormally less amount of precipitation scope reduced, or vice versa.

Key words: east of Northwest of China, extreme precipitation events, extreme drought and flood, trend