Fig. 1: Anomaly of greenness and snow cover duration.

a Infrared false-color SPOT 5 image (10 m resolution) showing the locations of the three study catchments (Lauzelle, Roche Noire, Mandette) in the above-treeline ecosystems of the southwestern French Alps, located between the Lautaret and Galibier passes. The black square marks the position of the FluxAlp weather station. b Standardized Anomaly of Greenness (SAG) derived from multi-temporal 10 m resolution SPOT 5 images collected during the 2015 growing season. For each pixel, SAG represents the standardized difference between the annual maximum of the normalized difference vegetation index (NDVI) and the mean NDVI for all pixels in a similar topographic context, defined by elevation within ±50 m and Diurnal Anisotropic Heating within ±0.1 (Methods). c Example of a 5 m resolution binary snow cover map derived from a RapidEye Level3A product (European Space Agency, https://earth.esa.int/eogateway/catalog/rapideye-esa-archive) acquired on 10-07-2010, highlighting the distribution of late-lying snowfields (in blue). The fractional snow-covered area (fSCA) represents 15.5% of the study area. d Distribution of SAG for snow-covered and snow-free pixels from the RapidEye image (c), categorized by slope classes. Boxplots within the violin plots show the median, first quartile, and third quartile of the SAG distribution. The comparison between the no-snow and snow groups using a one-sided t test (no-snow greater than snow) is significant (P < 0.001) for all three slope classes (t = 85.874, df = 25,067 for slope <15°; t = 69.97, t = 179.26, df = 91,372 for slope >15° and <30°; t = 69.97, df = 39,233 for slope >30°). Credit: a, European Space Agency (ESA Earth online).