Objective definition of monitoring index for extreme precipitation processes in Hu’nan province

Based on daily precipitation data at 97 ground weather stations from 1981 to 2010 in Hu’nan province, mutations of short-time precipitation sequence and process precipitation sequence were analyzed by methods of a second-order derivative analysis and a Cusp catastrophe model analysis. The results indicate that the maximum hourly accumulated short-time precipitation has two mutation points and both occur in the point of 12.0 hours and 6.1 hours respectively, while process precipitation has also two mutation points and both occur in the point of 10.0 days and 4.4 days. Percentage of duration of the maximum precipitation to the total process precipitation has two mutation points and both appear in the point of 10.0 days and 4.6 days. Two mutation points of maximum precipitation occur in the point of 10.0 days and 4.9 days. Thus, we establish a series of monitoring index of extreme precipitation process in Hu’nan province, including 1-6 hours and 12 hours maximum continuous precipitation, 1-5 days and 10 days maximum continuous precipitation, accumulated precipitation process and precipitation duration. The indexes have been verified by correlation coefficients of monitoring indexes of extreme precipitation processes with afftected and suffering rate of crop flooding disaster, and reduction rate of crop yield per unit.