Hydrological modelling using SWAT in a Complex Semi-Arid Watershed

Hydrological models have emerged as essential tools for examining the hydrological processes of complex watersheds addressing various environmental and water resource issues. This study focuses on modeling the hydrology of the Merguellil watershed in central Tunisia using the Soil and Water Assessment Tool (SWAT). The SWAT model is a physical modeling tool developed to forecast hydrological processes and is well-documented as an effective tool for resource water management. The primary objective of this research is to evaluate the SWAT model's performance in simulating monthly hydrological processes within the Merguellil watershed in central semi-arid Tunisia. Calibration of the model was conducted from 2002 to 2011, followed by a validation from 2012 to 2017. Sensitivity analysis identified key parameters, including Curve Number, Slope Length, and effective hydraulic conductivity, as the most sensitive. The findings demonstrate that the model exhibits satisfactory performance according to goodness-of-fit criteria during both the calibration and validation phases. The Nash–Sutcliffe Efficiency (NSE) were 0.65 and 0.41, respectively, for calibration and validation periods. The coefficient of determination (R²) and Kling-Gupta efficiency (KGE) are both equal to 0.7, the RMSE-observations standard deviation ratio (RSR) is less than or equal to 0.6, for calibration. The Percent Bias (PBIAS) indicates that the model overestimates the discharges by +23.5% during the calibration period. In addition, the runoff in Merguellil watershed demonstrated a notable spatio-temporal variability, significantly influenced by the complexity and heterogeneity of its environment.