Document Type : Research Article
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Abstract
The purpose of this study is regional frequency analysis of Annual Maximum 1-day Rainfall (AM1R) and Annual Maximum 2-day Rainfall (AM2R) using L-moments theory in Khorasan Razavi Province. For this purpose, the basic statistical tests include: homogeneity, independency and outlier data for AM1R and AM2R were surveyed in 123 rainfall stations. The province was divided into four regions based on cluster analysis, topography and spatial pattern of precipitation. Hydrology homogeneity was also controlled by running heterogeneity test for each region. generalized extreme value (GEV), generalized logistic (GLO), Pearson type III (PE3) and Log Normal type III (LN3) probability distributions were estimated for every region. To select the appropriate distribution of AM1R and AM2R data, the fitness was judged using an L-moment ratio diagram and the Kolmogorov–Smirnov test and GEVdistribution select . The regionally quantile estimateions for GEV distribution were also calculated for AM1R and AM2R data. In all of the Homogeneous regions, the estimated values of AM1R and AM2R from the obtained relations are close enough to the real data of return periods less than 200 years (The largest MAE was 0.0386). The average absolute error between the estimated and the observation values in each region is favorable, showing a high accuracy of the estimation.
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