Calibration and evaluation of SWRRB hydrological model for runoff simulation (Case study: Kasilian watershed)

Most of the hydrological systems are very complicated and it is not possible to understand them completely. Therefore, simplification is necessary to understand or control of a part of the system behavior such as water balance relationships. Hydrological models are simple structure of complicated systems in hydrological cycle in the nature. The first goal of a hydrological model is to predict complicated system function and evaluate the impact of any kind of changes on system behavior. This will help us to better understand processes of the system. In this research SWRRB hydrological model was used to simulate water balance relationship in Kasilian watershed located in Mazandaran province. SWRRB is a continuous hydrological model. This model was calibrated and evaluated in Kasilian watershed. The simulation error in calibration and evaluation steps was estimated using MAE, RMSE and NASH criteria. Significance and insignificance of difference between observed and estimated runoff values was evaluated using Z factor. Model sensitivity analysis with respect to the different variables was investigated. The result of this research showed that the model can simulate annual runoff more accurate than monthly runoff. On the other hand, in comparison between monthly and daily runoff, it can be seen that simulation of monthly runoff is more reliable than daily runoff. In this research, it has been shown that the model is sensitive to length of the data.