Select the best statistical distribution in estimating the rainfall return period using Smada software (Case study: Karaj city)

The main purpose of this paper is to evaluate and estimate the annual rainfall return period and provide the best statistical distribution. Therefore, the annual rainfall data of Karaj Synoptic Station has been used to estimate the rainfall with a return period of 200,100,50,25,5. Gift tests (x ̅), Rss, K-S were used to use the best statistical distribution and finally smada software was used to analyze the selected distribution. The results of the study show that among the statistical distributions used in this study, the distribution of the lognormal is the most appropriate distribution.