Evaluation of SCS model for flood characteristic prediction in an ungauged catchment considering effects of excess rainfall and base flow separation

Several studies are available to evaluate the soil conservation service (SCS) model in estimating flood characteristics in which different results were reported for the efficiency of the model. The selection of base flow and excess rainfall separation methods can have a significant impact on the efficiency of the SCS model. In this study, the impacts of three common methods of separating the base flow, namely straight line, fixed base and variable gradient, as well as two methods of estimating excess rainfall, i.e., Ø index and SCS method on the accuracy of the SCS model in Jong catchment in the northeast of Iran were investigated. To evaluate the accuracy of the model, the percentage error in peak, the percentage error in volume, the coefficient of determination and the Nash–Sutcliffe criteria were used. The results of the study show that in all investigated conditions, the estimated peak discharge is less than the observed values, and in most cases, the estimated flood volume is more than the observed flood volume. In general, the variable gradient method has led to the best results in estimating flood characteristics. Also, the SCS method improved the estimation of the hydrograph shape and the flood volume, and in turn, the Ø index resulted in an improved flood peak discharge. Finally, it was found that the combination of base flow separation – excess rainfall estimation of SCS – fixed base, was recognised as the best combination. Research highlights Results of the study highlight some scientific and applied details for flood estimation in ungauged catchments as interesting topics in geosciences, earth system science, natural hazards, and environmental sciences.