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 severalpotentially possible probability distributions of rainfall data. for this purpose, the chi-square, thekolmogrov-smirnov and the probability plot correlation coefficient (ppcc) methods as goodness offit tests are usually used. recently, l-moment ratio diagrams have been recommended to verify thegoodness 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 appropriateprobability distributions of regional rainfall data investigation with 95% acceptance regions in northwest of iran. for this purpose, 50 years of monthly and annual rainfall data records at 12 synopticstations were applied based on different evaluating criteria. the results of both ppcc procedure and lmoment diagram indicate that pearson type three probability distribution is the best probabilitydistribution 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.