<p>This study evaluates the impacts of climate change on the Naumure Multipurpose Project (NMP) and suggests adaptive measures for reservoir operation through dynamic rule curve modification. Future hydrological inflows were projected for six Global Climate Models (GCMs) of Coupled Model Intercomparison Project Phase 6 (CMIP6) under two Shared Socioeconomic Pathways (SSP245 and SSP585). These projections were bias-corrected by Linear Scaling method multiplicative for precipitation and additive for temperature - and subsequently simulated under the Soil and Water Assessment Tool (SWAT) to generate future streamflow. The resulting streamflow data were then incorporated into the Hydrologic Engineering Center’s Reservoir System Simulation (HEC-ResSim) model to analyze and optimize reservoir operation under both historical and projected hydrological regimes. Simulations were carried out for three future periods - near future (2015–2040), mid future (2040–2070), and far future (2070–2100) - to evaluate reservoir performance, hydropower generation, and irrigation reliability under changing climate scenarios. The findings indicate projected increases in precipitation and river discharge (25–179%) by 2100, which can be effectively managed through adaptive reservoir operation to enhance both hydropower production and irrigation reliability. Through iterative simulations, eight alternative rule curves were evaluated, among which Rule Curves 1, 4, and 7 performed best ensuring full irrigation reliability for the Kapilvastu Irrigation Project while enhancing hydropower generation at Naumure, Lamatal, and Surainaka by 27.23%, 14.62%, and 2.27%, respectively. These results demonstrate that future climatic variability can be effectively managed through adaptive reservoir operation, enhancing both energy production and irrigation reliability. The findings offer actionable insights for climate-resilient water management, emphasizing the integration of hydrological modeling into regional energy planning and water security policies to support sustainable infrastructure development in Nepal and other monsoon-dependent basins.</p> Graphical Abstract <p></p> <p>Graphical abstract descriptions: This study investigates the impacts of climate change on hydropower generation and irrigation reliability and proposed the reservoir rule curve under different climate scenarios in the Naumure Multipurpose Project (NMP), located in the West Rapti River Basin, Nepal. The top section highlights the study area of the West Rapti River Basin and its spatial datasets, including elevation, land use, and soil maps, which form the foundation for hydrological modeling. Future climate projections were developed using six bias-corrected CMIP6 Global Climate Models under SSP245 and SSP585 scenarios to capture a wide spectrum of potential hydro-climatic futures. The projections were embedded in the Soil and Water Assessment Tool (SWAT) for performing hydrological modeling, where calibration and validation ensured strong simulation of discharge. Finally, the Hydrologic Engineering Center’s Reservoir System Simulation (HEC-ResSim) was used for examining reservoir performance and optimizing operation strategies. The methodological framework enabled analysis of future climatic variability, projected discharges, and reservoir operations to assess energy generation and irrigation supply reliability. Results show significant increases in precipitation and temperature, leading to higher river discharge and potential energy gains, but with challenges during the dry season. To address this, eight new alternative operating rule curves for the reservoir were prepared and tested, where rule curves 1, 4, and 7 best performed by maximizing hydropower production while fulfilling irrigation water needs in their entirety. The findings highlight the importance of climate-resilient reservoir management strategies in ensuring energy and irrigation water supply, hence offering important implications for policy-making and infrastructure long-term planning under future climate change</p>