Comparative study of the best method for estimating maximum annual precipitation in selected stations of Haraz River

According to the objectives of the present study after reviewing the statistics and information of precipitation in Haraz watershed and due to the lack of long-term statistics in the study area, finally 3 stations of Panjab-Haraz,Karsang-Haraz and Mahmoudabad-Haraz in different parts of the river from mountain to plain in 44-year common statistical period from the water year of 1968-69 to 2011-2012 was selected for this study. After analyzing the changes in annual precipitation of the selected stations, the results of Residual sum of squares (R.S.S) test were extracted by the method of ordinary moments and the maximum likelihood were compared with the method of linear moments. Residual Sum of the Squares (R.S.S in the linear moment method were also calculated by a written computer program for the studied distributions .Based on the results of this study and using the scoring and ranking method, it is determined that in Panjab-Haraz station, the maximum likelihood method has the lowest R.S.S, with the total score of 6 has the best fit with the annual precipitation data and ordinary and linear moments methods with a total score of 15 are equally in the next ranks .At Karsang-Haraz station, the maximum likelihood method has a total score of 10 and the best fit with the annual precipitation data, followed by the ordinary moment method with a total score of 14 and the linear moment method with a total score of 15, respectively. At Mahmoudabad station the maximum likelihood method with obtaining a total score of 3 has been the best method selected at this station, followed by the ordinary moment and linear moment methods with a total score of 6 and 15, respectively.