Advanced hydrological assessment with SWAT+ under climate change: An integrated framework over large climate-sensitive and reservoir-regulated watershed.

Quantifying streamflow dynamics under changing hydroclimatic conditions is essential for effective water resources planning, particularly in reservoir-regulated basins. This study, for the first time, develops a dynamic reservoir-streamflow modelling framework to simulate historical and future streamflow in the Mahanadi River Basin (MRB), a large, climate-sensitive basin in India. The framework is driven by the latest version of the Soil and Water Assessment Tool Plus (SWAT+), with a dynamic reservoir operation module, and the CLIMEA-BCUD dataset (Climate Change for East Asia with Bias-Corrected UNet), a high-fidelity product derived from an ensemble of 19 CMIP6 GCMs. A thorough evaluation against benchmark station-level observations indicates a high degree of closeness of CLIMEA-BCUD in capturing historical precipitation and temperature variability (CC > 0.9, NSE > 0.85). A seasonal shift in monsoon rainfall patterns is observed in the future climate scenarios, with the peak moving from July to August. Additionally, more frequent moderate rainfall and prolonged wet spells are expected, intensifying flood potential. SWAT+ simulations developed for SSP2-4.5 and SSP5-8.5 scenarios project up to 30.7 % and 52.3 % rise in streamflow for about 15.2 % and 28.5 % rise in precipitation, respectively, during the far-future. Our observations also indicate that wet season flows (June-November) may increase by up to 61.3 %, while dry season flows (December-May) may decline by 34.1 % due to elevated evapotranspiration. This study presents a scalable framework to enhance streamflow resilience in regulated, climate-sensitive basins and offers critical insights for understanding hydrological responses and enabling climate-resilient water management.