The second physically based model used in this study was the HEC-HMS model. Runoff in the HEC-HMS model is simulated by analysing meteorological data through open channel routing (Shekar & Vinay 2021). The HEC-HMS physically based model was calibrated and optimised using 18 years of daily observed runoff data. Similar to the SWAT model, a sensitivity analysis was performed in the HEC-HMS model to determine the most sensitive parameters affecting the simulation of runoff. In the HEC-HMS model, the most sensitive parameters identified during model optimisation are listed in Table 4. For the HEC-HMS model, the identification of the most sensitive parameters during model optimisation was performed using a one-at-a-time approach. In this method, the value of one parameter was changed, while the others were held constant and the RMSE value was compared between the observed and simulated discharge values at the outlet of the catchment. The optimum values of the parameters vary between the sub-basins.