Comparative Evaluation of Model Sensitivity, Calibration, and Parameter Uncertainty in Streamflow Simulation Using SWAT and HBV Light in the Geba Watershed, Ethiopia

Abstract

Evaluating and simulating streamflow is extremely useful for managing water resources in almost all regions, particularly in arid ones. This study focuses on the performance of two hydrological models, HBV Light and SWAT, in streamflow simulation in northern Ethiopia. The models were evaluated using an ensemble modeling approach, which integrated Monte Carlo simulations for HBV Light and SWAT, while SWAT-CUP was used for calibration and validation. During the sensitivity analysis, key parameters controlling the model outputs were identified. For HBV Light, the parameters, K2, MAXBAS, and BETA, reflect subsurface processes, whereas SWAT, CN2, GWQMN, and SOL_AWC were used to control surface runoff. During calibration and validation, SWAT demonstrated statistically superior performance in modeling streamflow (R²=0.73, NSE=0.81) and (R² =0.72, NSE=0.72) respectively. While HBV Light recorded a performance of (R²=0.71, NSE=0.70) during calibration and (R²= 0.71, NSE= 0.71) during validation,which was closer to the observed streamflow. This indicates during the validation phase, SWAT still performed better but HBV Light demonstrated narrower predictive uncertainties at 95% along with more identifiability of the parameters that reduced the problem of equifinality. The bottom line of this case was that SWAT was statistically better, while HBV Light was more transparent and reliable with uncertainties. All things considered, both models could simulate streamflow, but their differences suggested that context-based choice would be optimal. While predictive consistency and uncertainty portrayal were most important, HBV Light was advantageous, and SWAT was better suited for use in cases that rank calibration accuracy above all else. The hydrology of the catchment could be better understood if streamline decision-making for the effective and sustainable management of water resources in the Geba Catchment and similar semi-arid areas were combined, or if multi-model ensembles were utilized.

Keywords: Streamflow simulation, Hydrological modeling, HBV Light model, SWAT model, Uncertainty analysis, Parameter sensitivity