Decade Variations of Precipitation Event Frequency, Intensity and Duration in the Northeast China

Against the background of global warming, study on climate extremes has become more important, especially the extreme precipitation events in Northeast China which is one of the most remarkable warming areas in China. Daily rainfall data of 93 weather stations in Northeast China from 1951 to 2002 are used to analyze the temporal and spatial variation of precipitation events, including rainstorm, heavy rain, light rain, extreme dry spell, extreme wetness spell etc. The spatial and temporal characteristics of precipitation events change are studied. The main conclusions are summarized as follows. The number of days both of the total rain events and the light rain decreases. The contribution of light rain to annual precipitation is obviously increasing, the contribution of mediummagnitude rain is slightly decreasing, and the contributions of heavy rain remains unchanged. The annual rain day has a significant decreasing trend, which is mostly due to the decreasing of light rain day. The intensity of annual precipitation shows a significant increasing trend due to the increasing of the intensity of light rain and rainstorm. The events of light rain are more frequent before the middle of 1980s, the events of mediummagnitude rain are more frequent after the middle of 1980s, and the rainstorm events have an obviously positive trend after the middle of 1990s. In the significant warming period of 1991—2000, the total days with rain events have an obvious decreasing trend, but the rainstorm day hasn't an insignificant change, though the intensity of rainstorm is building up in the analyzed period. Since 1980s, the climatic variation range of precipitation (57 mm) has also an obvious increasing trend with the global warming. The value of precipitation variation range (77 mm) in the significant warming period of 1991—2000 reaches the biggest since 1960s, which is about one and a half times of other period of 1960s of 52 mm and 1970s of 41 mm. The long dry spells (there is no rain for 10 days or longer) are with a significant increasing trend. The long wetness spells(there is rain for 6 days or longer)are with a significant decreasing trend. The long dry spells are highly related to drought. Against the background of a little change in the total precipitation amount, the distribution of precipitation has become more asymmetric. The rain events have an obvious trend of extremeness. In a word, the extreme trend of precipitation is a reality during the last half of the 20th century in Northeast China with the remarkable warming. The extremity brings drought and waterlog which is likely to become more severe due to the change trend. Adverse influence on environment, especially agriculture production, will be brought.