Modelling shallow groundwater in high elevation alpine catchments: opportunities and challenges

Understanding the interactions between cryosphere and groundwater is pivotal but challenging. This is primarily due to high spatial heterogeneity of subsurface properties and rare spatial in-situ measurements in such environments. Here we discuss the opportunities and challenges of modelling shallow groundwater in a high elevation glaciated alpine catchment: the Martell Valley in the central European Alps (northern Italy). We have performed extensive field measurements of hydroclimatic variables and sampling campaigns for stable water isotope analysis (δ²H, δ¹⁸O) since 2022, including river discharge, groundwater level, spring discharge, rainfall, snow, and glacier outlets. To infer additional insights on the system dynamics, we adopted the physics-based hydrological model WaSiM with an integrated groundwater module for hydrological process simulations. We find that (i) shallow groundwater increases nearly as quickly as streamflow to snowmelt and heavy rainfall, as shown by their hydrographs and annual isotope signatures. Because this quick groundwater response is rarely anticipated by the model, this highlights the need for improved subsurface parameterization in hydrological models. (ii) Surprisingly, subsurface lateral flow plays a minor role in river discharge generation at the study site, providing new insights into the hydrological processes in this environment. (iii) Lastly our results underline the challenges of integrating point-scale groundwater observations into a distributed hydrological model, with important implications for future piezometer installation in the field. Through our findings with this coupled modelling-field data study, we synthesize current challenges in modelling high alpine hydro(geo)logical processes.