ABSTRACT Monsoon climates exhibit pronounced seasonal contrasts, with the majority of annual precipitation concentrated in the wet season. This strong seasonality poses significant challenges for water resources management, especially in regions with competing demands such as irrigation, hydropower, and urban supply. Hydrological models like the Soil and Water Assessment Tool (SWAT) are widely used to simulate water fluxes in monsoon regions. However, SWAT's default Surface Conservation Service‐Curve Number (SCS‐CN) method and simplified groundwater module often struggle to represent seasonal dynamics in surface and subsurface hydrological processes. This study introduces two key modifications to SWAT: (1) a flexible calibration framework for the SCS‐CN method that allows users to adjust the initial abstraction coefficient (λ) to better match local hydrological conditions, and (2) a dynamic groundwater delay function that varies travel time (gwdelay) based on the day of the year to reflect seasonal recharge dynamics. The modified model was applied to the Rodeador watershed in central Brazil, a region strongly influenced by monsoon precipitation. Compared to the default model, the modified SWAT configuration improved daily streamflow simulation, increasing the Nash‐Sutcliffe Efficiency (NSE) from 0.59 to 0.66 and reducing percent bias from 15.2% to 8.7%. For key management‐relevant metrics, the modified model reduced deviations in monthly streamflow to below 10% during dry and normal years, while the default model exceeded 30% in the dry year. Annual minimum flow predictions of various durations (1–90 days) improved substantially, with errors reduced from over 70% in the default model to between 1% and 12%. The Julian date of minimum flow, which was misestimated by more than two months by the default model, was predicted within a few days of the observed date in the modified versions. Beyond improving simulation accuracy, the proposed modifications reduced predictive uncertainty, offering a more robust and transferable modelling framework for water management in monsoon‐affected regions. The enhancements are adaptable to other watersheds and can improve hydrological model performance where seasonal water scarcity and competing demands are pressing concerns.
Alves et al. (Sun,) studied this question.