Evaluating the Performance of Hydrological Models for Flood Discharge Simulation in the Wangchu River Basin, Bhutan

Flood has become a major hazard globally, and in Bhutan, with its steep terrain and erratic rainfall, it has caused significant economic damage in recent years. Given these challenges, there is a lack of accurate flood prediction and management strategies. In this study, therefore, we evaluated three hydrological models—Integrated Flood Analysis System (IFAS), Hydrologic Engineering Centre Hydrologic Modeling System (HEC-HMS), and Group on Earth Observation Global Water Sustainability (GEOGloWS)—and identified the most suitable model for simulating flood events in the Wangchu River Basin in Bhutan. Furthermore, we examined the models’ performance in a large and a small basin using the Nash–Sutcliffe Efficiency (NSE), Percent Bias (PBIAS), and Peak Flow Error (PFE) metrics. Overall, the GEOGloWS model demonstrated the highest accuracy in simulating flood in the large basin, achieving NSE, PBIAS, and PFE values of 0.93, 3.21%, and 4.48%, respectively. In the small basin, the IFAS model showed strong performance with an NSE value of 0.84. The GEOGloWS model provides simulated discharge but needs to be bias corrected before use. The calibrated parameters can be used in the IFAS and HEC-HMS models in future studies to simulate floods in the Wangchu River Basin and adjacent basins with similar geographical characteristics.