Study On The Frequency Distribution Of Short Duration Rainstorm And The Rainstorm Formula In Shanxi Province

Rainstorm and flood disaster is one of the most important natural disasters.With the social development and environmental changes, the impact and loss caused by heavy rain and floods are becoming more and more serious. The rainstorm formula has important theoretical value in the research of rainstorm characteristics and plays an important role in flood control and drainage.This paper takes Shanxi province 20 stations, five short duration rainstorm data as the basis research data. Using four methods to estimate parameters of the five frequency distribution;In accordance with the maximum coefficient of determination(Qd) and the minimum square sum(RMSE), compared the adaptability of different distribution;Calculating the storm intensity for different return period based on optimal assumed distribution and optimal parameter estimation; Analysis the suitable type of rainstorm formula in study area. Deriving the parameter of rainstorm formula by Levenberg-Marguardt method.The main conclusions of the study are as follows:(1)Using Moment method, Maximum Likelihood method, Probability Weighted Moment method and the Linear Moment method four parameter estimation methods to fit the five kinds distribution commonly used(P-Ⅲ distribution, Exponential distribution and Gumbel distribution, Normal distribution and The two parameters of the Lognormal distribution), obtained parameter values for different site and distribution under different parameter estimation methods.(2)According to the maximum coefficient of determination(Qd) and the minimum square sum(RMSE), evaluated the fitting degree of the five frequency distribution under four parameter estimation method. The results show that P-III frequency distribution had good fitting degree for different stations, different duration rainstorm,therefore it could be used as the theoretical frequency distribution for short duration rainstorm in the study area.(3)Parameter values estimated based on L-Moments Method are close to the parameter values estimated through the Probability Weighted Moment method.In accordance with the selection results of the maximum coefficient(Qd) and the minimum square sum(RMSE), L-Moment method is better than Moment method and Maximum Likelihood method.(4) Using mean root square error and the relative mean root square error as the judgment standard, compared the rainstorm formula for single return period and comprehensive rainstorm formula.The results shows that the rainstorm formula for single return period was applicable in the study area, and obtained the parameters of the rainstorm formula for each sites.