An integrated SWAT–SDSM–QDM framework for assessing climate change impacts in a climatic transition basin

Abstract In this study, a novel integrated hydrological–climate modeling framework combining the Soil and Water Assessment Tool, the Statistical DownScaling Model, and the Quantile Delta Mapping method was applied to the Kelkit Basin, which is located in a climatic transition zone. To the best of our knowledge, the joint application of these three components within a single integrated framework has not been previously reported in the literature. This approach enhances the reliability of local-scale climate and hydrological projections and provides a transferable methodological reference for other climate-sensitive basins. The model calibration and validation yielded satisfactory to very good performance, with NSE, R 2 , and KGE values ranging between 0.79–0.88, 0.84–0.89, and 0.83–0.92 in sub-basins with natural flow regimes, while the dam-affected sub-basin showed satisfactory validation performance (NSE = 0.50). Future projections indicate substantial changes in basin water potential. Under the SSP5 scenario, precipitation increased by up to 82% and blue water potential increased by 129–270% in the far future (2076–2100), depending on the sub-basin. In contrast, green water storage decreased by up to 8–13%, particularly during summer months, reflecting enhanced evapotranspiration and soil moisture depletion. Increases in green water flow may support plant growth in the short term; however, soil moisture losses could threaten agricultural productivity and ecosystem sustainability in the long term. In addition, the rise in blue water components increases potential flood risks. The findings demonstrate that the Kelkit Basin possesses a complex hydrological structure that contains both opportunities and risks in the face of climate change.