Fig. 5: Historical reconstruction of degree days (DD) and snow cover duration in late snow melting sites.

a Estimated DD from January 1st to mid-August (DOY = 227) over the past 250 years. We used quantile regression to adjust the long-term air temperature time series, either measured at the nearby weather station in Le Monêtier-les-Bains or reconstructed using the Histalp dataset, to FluxAlp (Methods). b Reconstructed SMOD for late snow melting sites corresponding to the EA, CF, and MS habitats (Fig. 2b, c and Supplementary Table 1). Time series are shown for each habitat, corresponding to the date when the median DD value for each habitat is reached. For readability, confidence intervals for SMOD estimates are shown only for EA. A SMOD in mid-August (vertical gray line) indicates a snow-free season of less than two months, which is insufficient for sustained plant growth and soil development. The black line represents the SMOD required to reach DD values of 800 °C (DD800). The bold lines in panels a and b represent a Gaussian filter (using sigma = 8). See Supplementary Fig. 6 for the goodness-of-fit estimates of the quantile regression models.