Linking grassland dynamics to snowmelt timing in the Western Pyrenees

Abstract. It is now well established that climate change modifies the snow cover regime in European mountains. However, the impact of snow cover changes on alpine ecosystems is not well understood. In this study, we assess how snowmelt timing affects alpine grassland growth (onset and evolution) in the western Spanish Pyrenees using eight years (2018–2025) of Sentinel-2 imagery at 10 m resolution. We combined satellite-derived snow melt-out dates (SMOD) with NDVI time series, meteorological data, and fractional snow-covered area (fSCA) to evaluate the temporal and spatial relationships between snowmelt timing and vegetation greening. Our results confirm that snowmelt consistently influences the onset of greening and regulates the timing of peak NDVI (annual maximum). However, short-term variations in melt-out timing had limited influence on the intensity of peak NDVI, which was more strongly linked to post-melt meteorological conditions. The spatial pattern of peak NDVI remained stable across years despite variable melt timing. Our observations suggest that site-specific characteristics – such as soil properties, microclimate, and vegetation composition – that can be linked to the long-term legacy of snow presence can exert a stronger influence on productivity than year-to-year snowmelt dynamics.