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

Flood has become a major hazard globally, and Bhutan with its steep terrain and erratic rainfall has caused significant economic damages in recent years. Given these challenges, there is a lack of accurate flood prediction and management strategies. This study, there-fore, evaluates three hydrological models—Integrate Flood Analysis System (IFAS), Hy-drologic Engineering Centre Hydrologic Modeling System (HEC-HMS), and Group on Earth Observation Global Water Sustainability version 1 (GEOGloWS)—and identifies the most suitable model for simulating flood events in Wangchu River Basin of Bhutan. Fur-ther, it also examined the model performance for Large and Small Basins using Nash-Sutcliffe Efficiency (NSE), Percentage Bias (PBIAS) and Peak Flow Error (PFE) met-rics. Overall, the GEOGloWS model demonstrated the highest accuracy in simulating flood in large basin, achieving the NSE, PBIAS and PFE values of 0.93, 3.21 and 4.48, re-spectively. In small basin, the IFAS model showed strong performance with an NSE value of 0.84, although the discharge was underestimated. The GEOGloWS model provides simulated discharge but need to be bias corrected before use. The calibrated parameters can be used in IFAS and HEC-HMS models to simulate flood in Wangchu Basin and adjacent basins having similar geographical characteristics for future studies.