Selection of Best Fitted Probability Distribution Function for Daily Extreme Rainfall of Bale Zone, Ethiopia

Abstract

Different methods are employed to predict extreme rainfall in hydrology. The most common among these methods is the Probability Distribution method. In this study in order to identify suitable probability distribution for estimating of daily extreme rainfall series for different record period and class type of 18 rain gauge stations had been collected from Bale zone of Oromia region, Ethiopia. After homogeneity and consistency test, data has been analyzed by easy fit 5.5 standard software and Microsoft excel for predicting extreme values. Four probability distribution functions (Normal, Log Normal, Log Pearson type III and Gumbel extreme value type I) were employed and three goodness of fit tests (chi-sqare test, correlation coefficient and coefficient of determination) were applied to select the best probability distribution function for the study area. According to easy fit and Microsoft excel output Log Pearson type III is the most fitting for daily extreme rainfall.

Keywords:   Extreme rainfall, Probability Distribution, Log Pearson Type III, Goodness of fit, Bale zone