Analysis and Zonation of Maximum 24-Hour Rainfall of Iran Using Wakeby Distribution and Geostatistic Technique

Investigation of spatial variability of maximum 24-hour rainfall is very important for assessment of water resources and forecasting of natural disasters. In this research, the most appropriate probability distribution to estimate the maximum daily rainfall in return periods of 2, 5, 25, 50 and 100 years using Easyfit software based on Kolmogorov-Smirnov test is Wakeby distribution. Wakeby distribution was fitted to maximum daily rainfall. Semi-variogram values for mentioned return periods were calculated and plotted using simple kriging method and were fitted to an appropriate model. Then Maps of isohyetal line were drawn for different return periods. Results of semi-variogram showed that fitted model to variogram of the maximum 24-hour rainfall in return periods of 2, 5, and 25 is Gaussian and in return periods of 50 and 100 is spherical distribution. Suitability of variogram model was evaluated with cross validation method and calculating ME and RMSE statistics. RMSE criteria was obtained less than %40 for all of return periods that shows the accuracy of estimatings. Simple kriging method is suitable for zonation of the maximum daily rainfall. Central Iran in all of the produced maps have lowest daily rainfall than other regions. Reason of differences in maps at different return periods is differences of rainfall values in mentioned return periods. In the other hand, homogeneous areas are closer to each other in terms of rainfall amounts in a return period.