The Variation Tendency of Heavy Precipitation Events in Different Grades During Recent 45 Years over Central China

In the context of global climate change, frequencies and intensities of various extreme climate events are also changing. Central China is located at mid lower reaches of the Yangtze River, where rainstorm flooding disaster caused by heavy precipitation almost occurs every year. So it is extremely necessary to research variation characteristics of heavy precipitation events in Central China, which has important effects on improving the forecast of heavy precipitation and reducing the loss in this area. The interdecadal spatial temporal change trend, break and periods characteristics of all grade heavy precipitation events are studied using daily raingauge data of 84 weather stations from 1961 to 2005. These data are analyzed in terms of several modern statistical test methods such as percentile, trend coefficient, Monte Carlo statistical test, Mann Kendall break detector, Morlet wavelet transform etc.The results show that thresholds of heavy precipitation for 10%, 8%, 5% and 2% percentile is 24.7 mm, 28.6 mm, 37.6 mm and 57.8 mm by area averaged, respectively. The mean and standard deviation of heavy precipitation and raining days decrease with the percentile, variation coefficients of those increasements; while the mean, standard deviation and variation coefficient of intensity all rise gradually. As for spatial distribution, the heavy precipitation rises from Henan to Hunan and Jiangxi, the raining days rise from north to south. The intensity is lower in western Henan, northwestern Hubei, some parts of southern Hunan, and higher in the mid lower reaches of the Yangtze River, from eastern Hubei to northern Jiangxi, and some parts of northwestern Hunan. For a fixed grade, the heavy precipitation shows stronger linear trend than raining days, and linear trend of intensity is the weakest. The total heavy precipitation, raining days and intensity by area average show increasing trends in all grades. The total heavy precipitation in Grade Ⅳ and Ⅲ passes the 0.1 level test, and have distinct rising trend. The linear trend coefficients of total heavy precipitation, raining days, and intensity in different weather stations show various characteristics. With the percentiles decreasing, the trend coefficients show a decreasing trend in mid lower reaches of the Yangtze River from Yichang to its east, while opposite trend appears in southern Hunan and southern Jiangxi. For all grades, the total heavy precipitation breaks congruously in 1993, and shows a rising trend. The raining days breaks during the end of 1980s and the beginning of 1990s. The intensity begins to strengthen from 1994, but becomes unobvious after the year of 2000. For all grades, the heavy precipitation, raining days and intensity change regularly at an interdecadal period of 12—14 years and a short term period of 6—9 years.