Incorporating IPCC RCP4.5 and RCP8.5 Precipitation Scenarios into Semi-Distributed Hydrological Modeling of the Upper Skawa Mountainous Catchment, Poland

Mountain catchments in Central Europe are highly susceptible to flash floods. To inform local adaptation, this study quantifies the future flood response of a Polish Carpathian catchment (Upper Skawa, 240.4 km2) to Intergovernmental Panel on Climate Change (IPCC) scenarios. A semi-distributed HEC-HMS model was calibrated and validated using observed flood events (2014–2019). Future hydrographs were then simulated using the delta change method for RCP4.5 and RCP8.5 (near- and long-term horizons). The validated model showed high predictive accuracy. Results indicate a consistent trend towards a polarized hydrological regime, with increased spring/autumn flood peaks and decreased summer flows. This trend is significantly amplified under the RCP8.5 scenario, with long-term peak flood increases approximately double those of RCP4.5. The catchment’s non-linear response further compounds these impacts. These findings suggest a future of heightened seasonal flood risk and emerging summer water scarcity, implying that existing infrastructure, designed for historical stationarity, may be insufficient. This study provides a quantitative evidence base for re-evaluating regional flood risk policies and developing integrated adaptation strategies.