Study on Characteristics and Change Trend of Extreme Rainfall in the Jianghuai Region

The daily rainfall data from May to September of 71 stations in the Jianghuai region from 1961 to 2011 with no missing data were used to introduce the GPD (Generalized Pareto Distribution) based on the POT (Peaks- Over-Threshold) method in a study of the spatial distribution of extreme rainfall characteristics and trends. The results indicate that the maximum thresholds are at the border of Anhui and Jiangxi, whereas smaller thresholds are in northwest and southeast. The trends of the thresholds are positive in most places. At the stations in eastern Hubei and northern Jiangxi, the trends are more than 0.8 mm (10 a)^-1 and pass the 0.01 significance level of the Mann-Kendall test. In the mid-east region, extreme rainfall is nearly continuous; therefore, an automatic declustering scheme is used to select the independent extreme events exceeding the threshold. The largest values of scale parameter are in the south, whereas in areas northwest, southwest, and north of the Huaihe River, the values are smaller. In most parts of the Jianghuai region, the trends of scale parameter are positive, which indicates a greater occurrence probability of maximum rainfall. The border region of Anhui, Jiangxi, and Hubei has the highest probability of extreme rainfall, whereas the probabilities are lower in the northwest, southeast, and middle parts of Anhui. The trends of extreme rainfall are positive in most places, particularly in the Dabie mountains nearby and in eastern Henan, where the trends of 2-a and 20-a return levels are more than 6 mm (10 a)^-1 and 20 mm (10 a)^-1, respectively.