Evaluation of the Streamflow Simulation by SWAT Model for Selected Catchments in Mahaweli River Basin, Sri Lanka

This study examines the skills of the Soil and Water Assessment Tool (SWAT) for simulating the monthly streamflow in five catchments of the Mahaweli River Basin (MRB). Daily rainfall (43 rain gauges), terrain, land use and land cover, soil, and daily streamflow (5 stations) were used to run the SWAT model. The Calibration Uncertainty Procedure (SWAT-CUP) is adopted for model calibration (1998–2006) and validation (2007–2014). The model performance was evaluated using the Nash–Sutcliffe efficiency (NSE), coefficient of determination ( R 2 ), percent bias (PBIAS), and deviation of runoff volumes ( D v ). The results revealed that SWAT is able to reproduce the observed monthly variation of streamflow in 4 catchments, satisfying the model performance evaluation criteria ( R 2 = 0.5, NSE = 0.5, and PBIAS = ± 25). However, the model shows overall low performance in the catchment with extensive human intervention. The results further demonstrate that SWAT simulated peak flow events in the four catchments with moderate to a reasonable agreement (− 20