6. Workshop Alpine Hydrologie

Snow is a critical part of the water cycle for many ecosystems, as snowmelt delivers a reliable water supply that sustains vegetation productivity during the growing season. However, the increasing frequency of snow droughts (periods of anomalously low snow water equivalent (SWE) relative to the climatological mean) poses a growing threat to snow-dominated regions. Reduced SWE leads to an earlier onset of the growing season and a decrease in late-season water availability, both of which directly impact terrestrial vegetation productivity. Alpine ecosystems are particularly vulnerable, as they depend almost entirely on snowmelt for growing-season water supply and have already experienced sharp declines in snowpack depth and duration under current warming. Despite its ecological importance, the impacts of snow droughts on GPP in these regions remain poorly understood. In particular, how responses vary across ecoregions and whether growing-season precipitation amplifies or offsets snow drought effects.

Here, we investigate how snow droughts have affected gross primary productivity (GPP) across different alpine ecoregions over the past three decades. Using the LPJmL dynamic global vegetation model alongside three observational, gridded GPP products (FLUXCOM, NIRv, VODCA2GPP) and ERA5-Land snow data, we analyze the seasonal and cumulative distribution of GPP anomalies under snow drought conditions across ecoregions and aridity classes, revealing different responses between energy-limited and water-limited ecosystems. In energy-limited regions, snow drought conditions can extend the growing season and enhance spring productivity. By contrast, water-limited regions show consistent GPP suppression, which is further amplified when snow drought co-occurs with low spring precipitation.

Our results advance understanding of how snow droughts are reshaping vegetation productivity across climate regimes and provide new insights into ecosystem vulnerability under a changing climate.