Changing controls on low flows in the Wiese catchment (southern Black Forest, Germany) under climate change

Study Region: The Wiese catchment (454 km 2 ) in the southern Black Forest, Germany, is a snow-influenced mountain catchment that has undergone substantial hydrological changes during the 20th century. Understanding how the dominant controls on low-flow discharge have evolved over time is essential for sustainable water management under ongoing climate change. Study Focus: This study combines long-term discharge observations (1930–2019), process-based hydrological modelling with HEC-HMS , and bias-corrected CMIP6 climate projections to investigate historical and future low-flow discharge conditions. Historical low-flow discharge indicators (NQ, MN7Q, and Q 95 ) were analysed together with projected changes under the SSP2–4.5 and SSP5–8.5 scenarios (2015–2099). Historical analyses show that minimum low-flow discharge indicators increased during the late 20th century, consistent with documented land-use change, reduced industrial water use, declining agricultural irrigation, and climatic variability, although their individual contributions cannot be quantified. New Hydrological Insights for the Region: The projections indicate declining mean discharge and low-flow discharge indicators towards the end of the 21st century, with substantially stronger reductions under SSP5–8.5 than under SSP2–4.5. More importantly, the study demonstrates a shift in the dominant controls on low-flow discharge. Whereas historical low-flow characteristics are consistent with the combined influence of catchment changes, anthropogenic water use, and climatic variability, future low-flow discharge conditions are primarily associated with projected climatic forcing. This process-based perspective extends conventional climate impact assessments by linking historical hydrological change with future climate projections and provides new insights into evolving low-flow controls in mountain catchments.