Trend assessment of snow persistence in the Pyrenees based on Landsat imagery

A precise quantification of the spatio-temporal dynamics of snow cover is essential to assess the impact of climate change on mountain ecosystems, particularly in mid-mountain regions of southern Europe such as the Pyrenees. This study analyses the evolution of Snow Persistence (SP), defined as the fraction of time that snow remains on the ground, from 1984 to 2024 in the main river basins of the western Catalan Pyrenees. The analysis is based on remote sensing techniques using historical Landsat time series, with snow cover identified through the Normalized Difference Snow Index (NDSI). The results reveal a decline in SP across 73 % of the study area, indicating a transition from permanent winter snow cover to a more intermittent snow regime. Snow line elevation shows that seasonal snow cover during the 2014-2024 decade was located, on average, 267 m higher than during the 1984-1994 decade. The multiple regression model including altitude and solar irradiation explained 47.4 % of the spatial variability in SP, with a positive effect of altitude and a negative effect of solar radiation. Despite some methodological limitations, mainly related to temporal resolution and radiometric inconsistencies in Landsat Collection 2 Level 2 images, the results provide robust evidence of significant changes in snow dynamics.