The Study On Statistical Characteristic And Change Of Extreme Rainfall Over Jianghuai Region

Using the daily rainfall data from May to September of71stations over Jianghuai region with no missing from1961to2011and a similarly percentile method to ensure thresholds varying with time, then we acquire independent extreme events with an automatic declustering scheme, introduce the Generalized Pareto Distribution (GPD) based on Peaks-Over-Threshold (POT), build statistical distribution models of daily extreme rainfall and the multiple regression interpolation, study the statistical characteristic and trends by thresholds and scale parameters varying with time, preliminary discuss the influence of Southern Oscillation Index (SOI) which are reflected the ENSO circulation to the model parameters. The results indicate that:(1) The maximum thresholds of Jianghuai region extreme rainfall are at the border of Anhui and Jiangxi, while the smaller thresholds are in northwest and southeast, the trends of thresholds are positive in most places, the stations at the east of Hubei and the north of Jiangxi, the trends are more than0.8mm/10yr. The largest values of scale parameter are in south, while in northwest, southwest and north of Huaihe River, values are smaller; in most parts of Jianghuai region, the trends of scale parameter are positive, the maximum trends are around Dabie Mountain and Henan eastern, the trends are more then0.2mm/10yr. The border of Anhui, Jiangxi and Hubei has the biggest probability of extreme rainfall, the probability that an event of120mm/day occurs at least once within2-yr and20-yr return period are more then0.8and0.9, while in the northwest, southeast and middle part of Anhui the probabilities are lower. After the multiple regression interpolation of precipitation contains latitude, longitude, elevation gradient and so on, the interpolation weaken the spatial difference of trends of thresholds and scale parameters.(2) The trends of extreme rainfall are positive in most places, especially in Dabie mountains nearby and the east of Henan, with the combined action of scale parameter increase and threshold increase, the trends of2-yr and20-yr return level are more than6mm/10yr and20mm/10yr respectively. The large scale moisture change has not obvious influence to the change of extreme rainfall, but in the whole Jianghuai region, the trends of vorticity are positive, especially around Dabie Mountain the vorticity increase obviously, the cyclone circulation intensify, convergence upward movement intensify, making here to be one of the most trend increase significantly place.(3) Jianghuai region summer extreme rainfall has prominent positive correlation with the sea surface temperature (SST) of northwest of Pacific Ocean, the middle-east equator Pacific Ocean and the Indian Ocean central, and the correlation index are positive. Compare with SOI high years, the threshold of extreme rainfall and the GPD scale parameter are both bigger in SOI low years, the maximum are in the border of Anhui, Jiangxi and Hubei, the return level of the2-yr and20-yr return period are more then160mm/day and330mm/day, it’s easier to occur extreme rainfall.