Calculation of Water Balance Components in Ungauged Watersheds Using the Conceptual Model of Thomas Water Balance and Satellite Products

Water balance is one of the most important issues that should be paid special attention in the discussion of water resources management and as a result of decisions and plans for water consumption in different sectors. In this paper, using remote sensing products, the conceptual model of Thomas water balance (abcd) in a basin with semi-arid climatic conditions was calculated and evaluated. First, the monthly output of IMERG satellites and the re-analysed temperature of ERA5 were compared with ground-based measurements. Evaluation results of these products using five statistical indicators including Pearson correlation coefficient (R), root mean square error (RMSE), mean absolute error (MAE), Nash-Sutcliffe efficiency coefficient (NS) and deviation coefficient (BIAS) in the Zarandeh sub-basin located in Neishabour region shows their high accuracy and correlation with observations. Then, using these products and GIS, the conceptual model of Thomas for this sub-basin was developed in MATLAB software and its performance in basin runoff simulation was investigated. Fuzzy numbers and the Monte Carlo method were also used to reduce uncertainties in model parameters. This model was optimized with two different objective functions of Nash-Sutcliffe efficiency coefficient and determination coefficient. The results show the high accuracy of the abcd water balance model using remote sensing products in the study area and well simulation of the discharge behavior.