Snow2HyDro — the propagation of snow to hydrological droughts

The winter of 2024/2025 was marked by a pronounced snow drought—an exceptionally low‑snow year—particularly in Grisons. This event was driven by a combination of low winter precipitation and warm temperatures. The snow drought subsequently propagated into a hydrological drought in spring 2025, with far‑reaching consequences for the Alpine Rhine catchment. Notably, spring water levels in Lake Constance reached the lowest levels observed since 1972. Such conditions affect multiple water resources management sectors, including hydropower generation, agriculture (irrigation demand), transportation (shipping on Lake Constance), and ecosystems.

Historically, snowmelt has contributed around 55 % of the annual streamflow of the Alpine Rhine River (Diepoldsau). Snow has therefore played a crucial role in buffering drought impacts by serving as a form of natural storage. However, rapid cryospheric change driven by climate change is increasingly disrupting the balance between upstream water availability and downstream water demand. At present, our understanding of the resilience of Switzerland’s multifunctional landscapes to snow drought impacts remains limited, as does our knowledge of the extent to which society and key sectors must adapt to these evolving conditions. This raises the question: to what extent do snow droughts—such as the event observed during the winter of 2024/2025—propagate into sector-specific impacts downstream? This question is particularly relevant given that snow droughts have already increased in both frequency and intensity and are projected to intensify further under ongoing climate change.

The Snow2HyDro project responds directly to the WSL call by estimating the impacts of snow droughts on hydrological drought hazards in the Alpine Rhine basin. Using the physically-based and spatially distributed hydrological model WaSiM (500x500m), we will develop an integrated modelling framework based on observation-driven storylines to (a) assess system resilience to drought, (b) quantify the impacts of snow droughts on the energy, transportation, and agricultural sectors, and (c) identify sector-specific adaptation needs. The project’s outcomes will constitute an important first step toward developing targeted and robust climate adaptation strategies.