Past and Future Evolution of the Gébroulaz Glacier. Modelling the impact on the Hydrology of the Doron des Allues in the Vanoise Massif

The Alps, often referred to as Europe's water tower, are undergoing profound changes as a result of climate change. Declining snow cover, accelerated glacier retreat, and increasingly severe periods of low flow raise urgent questions for water resource management, biodiversity, and energy security. Hydropower, one of the pillars of the European renewable energy strategy, is particularly exposed to these changes. To understand and anticipate these impacts, it is necessary to have detailed modeling of Alpine hydrological systems, combined with reliable climate projections.

To meet these challenges, the spatially distributed hydrological model MORDOR-TS (Garavaglia et al., 2017; Rouhier et al., 2017) now includes an explicit glacier component to simulate glacier dynamics in warming scenarios (Rouzies et al., 2024). Applied to the Isère basin in the French Alps, this model supports strategic decisions relating to hydroelectric exploitation by simulating hydrological responses at the basin scale under different future climate scenarios (Le Lay et al., 2022). However, glaciers remain relatively poorly instrumented today, and their ice volumes are often poorly known, making such modeling inevitably imprecise. In this context, local observations and modeling produced by glaciologists are valuable for better quantifying the relative contribution of glaciers to river flows and improving the robustness of hydrological projections.

This study focuses on the modeling of a representative alpine glacier in the Vanoise massif, which feeds the Doron des Allues River. On this glacier, combining historical glaciological monitoring with radar-based surveys of current geometry and ice volume has enabled a detailed modelling of the glacier geometry, its evolution and meltwater discharge throughout the 21st century. These data are used to refine glacier representation in the MORDOR-TS hydrological model —surface area, volume, and meltwater flows—improving the reliability of basin-scale hydrological simulations, distinguishing between precipitation-driven and glacier-driven contributions. Results confirm strong consistency between the local glaciological model and the regional hydrological model and highlight pathways for further parameterization improvements.

The glacier is projected to almost completely disappear by 2100, with cascading impacts on discharge regimes. Beyond reduced mean flows, significant shifts in seasonal patterns and diminished summer flows are expected—posing challenges for hydropower production, ecosystem resilience, and water allocation. These results highlight the importance of coupling regional  hydrological models with high-resolution glaciological data to improve the robustness of climate impact assessments in mountain regions.

These findings underscore the urgency of adaptation strategies for mountain water resources in a warming climate. They also illustrate the value of coupling large-scale hydrological models with high-resolution glaciological data to support energy planning and climate resilience across Europe’s alpine regions.