Evaluation of Semi-distributed (SWAT) and Lumped (SMAR) Hydrological Models in Rainfall-runoff Estimation and Simulation, Case Study: Ojan chay drainage basin

One of the most important solutions for the principled and correct management of water and soil in basins is to use hydrological models for simulation of rainfall-runoff processes, which estimate and predict the components of the water balance, including runoff, evaporation, transpiration, and infiltration, especially in basins without data or with incomplete data. In this study, the water balance of Ojan Chai basin was simulated by the SWAT semi-distributed and SMAR models for 20 years (2002-2021). The SUFI-2 algorithm was used in the SWAT model and the genetic algorithm optimizer was used in the SMAR model for calibration (2005 to 2016) and validation (2017 to 2021).The simulation results in the calibration phase with the objective functions of the Nash-Sutcliffe efficiency (NSE), coefficient of determination (R²), and RSR were equal to 0.80, 0.81, and 0.45, respectively, and for validation, 0.74, 0.75, and 0.51, respectively, which indicates the high efficiency of the model in simulating the water balance. For the SMAR method, the Nash-Sutcliffe coefficients (NSE) and R² were obtained as 0.60 and 0.56 in calibration and 0.625 and 0.67 in validation.Both of these models perform better in simulating the baseflow and average flow rates than the maximum flow rates; however, the matching of the simulated flow rate with the observed flow rate in the SWAT model is superior to that of the SMAR model, which is due to the consideration of spatial changes in this type of model. Considering the very good performance results of the models, it is suggested that they be used in watershed protection measures and water and soil management.