Assessment of Goodness of Fit Methods in Determining the Best Regional Probability Distribution of Rainfall Data

One of the main steps in regional rainfall analysis is to determine the most appropriate of several potentially possible probability distributions of rainfall data. For this purpose, the chi-square, the Kolmogrov-Smirnov and the Probability Plot Correlation Coefficient (PPCC) methods as goodness of fit tests are usually used. Recently, L-moment ratio diagrams have been recommended to verify the goodness of fit of various probability distributions to regional hydrological data such as rainfall. Therefore, the PPCC and L-moment procedure were applied to examine the most appropriate probability distributions of regional rainfall data investigation with 95% acceptance regions in north west of Iran. For this purpose, 50 years of monthly and annual rainfall data records at 12 synoptic stations were applied based on different evaluating criteria. The results of both PPCC procedure and L-moment diagram indicate that Pearson type three probability distribution is the best probability distribution for fitting rainfall data in north west of Iran, while the L-moment approach is able to test fitness of many samples using a single diagram.