Assessing the Impacts of Climate Change on Hydrological Processes in a German Low Mountain Range Basin: Modelling Future Water Availability, Low Flows and Water Temperatures Using SWAT+

This study assesses the projected impacts of climate change on hydrological processes in the Gersprenz catchment, a representative low mountain range basin in central Germany, under the RCP8.5 scenario. Using the SWAT+ model and a bias-corrected climate projection ensemble, it simulates the temporal and spatial dynamics of water availability, discharge and water temperature through 2100. The results indicate a substantial reduction in seasonal discharge, with summer minima decreasing by 85% and autumn minima decreasing by 38% compared to the baseline. Rising air temperatures drive substantial warming, with maximum summer water temperatures projected to exceed 28 °C, increasing thermal stress on aquatic ecosystems. Spatial analysis reveals strong variability: Southern subcatchments, located in the upstream part of the catchment, face severe water deficits, while groundwater-fed springs provide localized thermal refuges but with limited buffering capacity. Northern regions generally show higher resilience, with exceptions. The findings highlight the fine-scale sensitivity of hydrological processes to climate change, shaped by catchment characteristics and amplified by natural seasonal variations. This study presents a framework for identifying spatio-temporal hotspots of water scarcity at the subcatchment scale, providing a basis for spatially targeted adaptation strategies to mitigate the impacts of climate change on regional water resources and ecosystems.