Comparison physiographical space based interpolation and Linear moments methods for regional flood frequency analysis in Mazandaran Province

The physiographical and climatological attributes of basins and maximum annual flood statistics were obtained from 38 hydrometric stations of Mazandaran province with minimum and maximum statistical periods 13 and 56 years. The first، homogenous regions in the physiographic space based on neighborhood approach were determined by using physiographical space based interpolation (PSBI) method. The Principal Component Analysis was used to design physiographic space using the six physiographic variables affecting the flood. The exponential model had the best fit to semi-variogram model in 10، 20، 50 and 100 year return periods، and regional estimates obtained using ordinary Kriging technique based physiography space. In order to evaluated the accuracy results using L-moments method for regional flood frequency analysis. In this method Ward hierarchical clustering has been used to the determination of homogeneous regions. Homogeneity areas were adjusted by using homogenous and discordancy tests. Using goodness-of-fit Z DIST the Generalized Logistic distribution was selected for all clusters as the best regional distribution and regional estimates obtained by parameters selected distribution. Finally، performance methods evaluated using Jack Knife procedure and the four statistical indexes BIAS، BIASr، RMSE، and RMSEr. Results showed that the PSBI method provide better performance than the L-moments at the four indexes considered and improving estimated by increasing the return periods، while the L-moments offers better performance for short return periods.