Performance Evaluation of WetSpa Hydrological Model for Runoff Simulation in Semi-arid Climatic Conditions (Case Study: Menderjan Basin)

The application of hydrological models in watersheds has always been considered by water resources researchers. This subject is of special importance in arid and semi-arid regions due to the greater complexity of hydrological processes in these region. In this research, the efficiency of WetSpa distributed hydrological model in Menderjan semi-arid basin has been evaluated and the sensitivity analysis and uncertainty analysis of the model parameters have been performed using PEST software.  Moreover, the efficiency of the Extended Kalman filter in improving the results has been investigated. The Nash-Sutcliffe coefficient for the calibration and validation periods was 0.63 and 0.58, respectively, confirming that the WetSpa model has a good performance in runoff simulation in Menderjan basin. The results of sensitivity analysis also show the high sensitivity of Kg and K_ss parameters and the low sensitivity of G_max and P_max parameters in the study area. Moreover, the results of uncertainty analysis are generally consistent with the results of sensitivity analysis and indicate the high certainty of sensitive parameters and the low certainty of non-sensitive parameters. The results of applying Kalman filter also show the improvement of the results. So that the Nash-Sutcliffe coefficient increased from 0.63 to 0.71 in the calibration period and from 0.58 to 0.69 in the validation period.