Frequency Analysis of Maximum Daily Rainfall in various Climates of Iran

    In this research in order to frequency analysis of maximum daily rainfall in various climates of Iran the data of 40 synoptic rain gauges collected in 40 years period i.e., 1973 to 2012 were used. These stations are located in various climates of Iran according to De Martonne climatic classification. At first, input of data to HYFA package was performed. The mentioned package includes seven probability distribution functions such as normal, two- and three-parameter lognormal, two-parameter gamma, Pearson and log-Pearson type III and extreme value type I or Gumbel. Then the data were fitted to seven mentioned distributions. HYFA estimates the parameters of the distributions by the methods of moments and maximum likelihood. The best distribution for each station was determined using mean relative deviation and mean square relative deviation as goodness of fit tests. The results showed that the suitable distribution for 29 stations is three-parameter lognormal, for five stations is two-parameter gamma, for two stations is two-parameter lognormal, for four stations is extreme value type I or Gumbel. Also, this study shows that the maximum daily rainfall in various climates of Iran can be analyzed with similar probability distribution functions. On the other hand, in similar climates, one could not use the same probability distribution functions for analyzing the data.