A model-based methodology for the delineation of complex alpine spring catchments

Spring catchments in Austria are frequently located in alpine regions that are strongly exposed to the effects of global warming. To predict their impact on spring flow, the delineation of hydrological catchments establishes the link between atmospheric input, catchment characteristics, and aquifer properties. This study proposes a delineation methodology that combines a lumped-parameter model with the analysis of stable isotope data. The model includes a semi-distributed snow module (CemaNeige) and a rainfall-runoff model (GR4J), which were applied iteratively to a set of potential catchments of varying extent and location to simulate spring flow. Constraining the models by spring flow data and remote sensing of snow cover distribution allowed us to differentiate plausible catchments from implausible ones. The mean catchment elevation was estimated based on stable hydrogen and oxygen data collected monthly at the springs. The proposed methodology was tested at two karst springs draining geologically complex catchments in different mountain ranges of the Northern Calcareous Alps, where the hydrological catchments deviate strongly from the orographic ones. The catchments lie mainly in mountainous plateau regions that are characterized by high altitudes and long-lasting snow cover. The model results and isotope analysis are in line with additional, independent information based on tracer experiments, structural geology, and speleology. The proposed methodology provides a quantitative, model-based approach to delineate plausible spring catchments in high alpine and complex hydrogeological settings. It thus forms the knowledge base for sustainable management of alpine freshwater resources under a changing climate.