An Analysis of the factors Affecting Flooding Severity in Iran

Understanding the flooding phenomenon and its effective factors is an essential prerequisite of its control and management. This phenomenon is influenced by hydrological, climatic and physiographic factors, as it has always been one of the most important issues in hydrology. Using the overlapping of the climate and the border maps of the country, catchments of each climatic region were demarcated. Furthermore, 314 hydrometry stations with a common period (1976-2011) in six climatic zones were selected. The instantaneous peak discharge value was calculated for a 50-year return period. 15 hydrological, climatic and physiographic parameters affecting the flood severity, namely average altitude, catchment area, the Gravelius coefficient, the slope, the main river length, the annual average precipitation, the average number of rainy days, the base flow index (BFI), the hydrograph recession coefficient (K), the curve number (CN), the permeability and the flow duration curve indices (FDC indices) of, Q2, Q5, Q10, Q20, were calculated for each catchment. The factor analysis after data standardization was performed in order to select the most important independent factors affecting flooding severity for each climatic region and the regression between the Flooding severity index and the selected factors in different climate zones were extracted and analyzed. Results indicated that the parameters used in all of the climatic regions explained more than 74% of the variance of the data. Common parameters in the first class of effective factors in all of the climatic zones were different flow parameters of (BFI, K, FDC indices), along with some parameters that were related to the intrinsic characteristic of the catchment, such as the CN and permeability. The flow exceedance value of, Q2, Q5, Q10, Q20 in all of the climatic zones were ranked first and may be recommended for estimation and prediction in the ungauged catchment. The normal distribution of errors and the coefficient of Durbin Watson (between 1.5 and 2.5) reflect the confidence of the regression equations to estimate the Flooding severity in the ungauged catchments in the different climatic zones.