Wetter futures under climate-driven rainfall and streamflow shifts in a tropical river basin

Accurate streamflow simulation under changing climate is essential for effective water resource management and disaster risk mitigation in river basins prone to hydro-meteorological extremes. This study employed the Soil and Water Assessment Tool (SWAT), calibrated using multi-site rainfall and discharge observations, together with bias-corrected climate projections from the NASA Earth Exchange Global Daily Downscaled Projections–Coupled Model Intercomparison Project Phase 6 (NEX-GDDP-CMIP6), to simulate historical and future streamflow in the Chaliyar River Basin (CRB), India. Future projections cover 2025–2095 under two Shared Socioeconomic Pathways (SSP2-4.5 and SSP5-8.5), considering the near future (2025–2060) and far future (2061–2095). The multi-model ensemble projects an increase in mean annual rainfall, accompanied by more frequent and intense extreme rainfall events, resulting in an increase in mean annual streamflow of up to ∼25% by the far future. The basin is also projected to experience an earlier onset and delayed withdrawal of the rainy season, with increased flows during pre-monsoon, monsoon, and post-monsoon seasons. Overall, the CRB is expected to transition towards a wetter hydrological regime, with increased flood risk in downstream areas. Despite limited rainfall and discharge observations, the findings provide a scientific basis for climate-informed flood risk management and water resource planning under future climate change.