Author(s): Youness Ouassanouan; Morgan Abily
Linked Author(s):
Keywords: Apls snow cover; MODIS snow products; Snow cover duration; Snow-elevation relationship; Trend analysis
Abstract: Understanding the spatio-temporal variability of snow cover in Mediterranean Alpine basins is crucial for assessing climate-driven impacts on water availability. The present study employs the 8-day MODIS snow data from 2002 to 2025 to assess snow cover duration (SCD), snow cover extent (SCE), and their variability across the Var watershed (southeastern France). Snow typically persists for a period of five to six months at elevations above 1,500 m, where accumulation is most reliable. However, the watershed-wide seasonal snow-covered area ranges between 500 and 1,500 km², reflecting strong interannual and seasonal fluctuations. Elevation is the primary driver of SCD variability, creating strong contrasts between mid-elevation areas (<1500 m) and high-elevation zones (>1500 m). Change-point analysis reveals three distinct SCD regimes over the 23-year period, with watershed-wide averages of 2.3, 2.2, and 1.8 months, and corresponding values of 4.9, 4.7, and 4.05 months for areas above 1500 m. These shifts indicate a net reduction of up to 15 days of snow across the entire Var watershed and 25 days at elevations above 1500 m between 2002 and 2025. In accordance with the broader cryospheric changes observed in the southern Alps, significant negative SCD anomalies were recorded during the period 2022-2025, even at elevations where snow is typically most protracted. Snow cover extent also shows a declining trajectory, with ~10% reductions of the whole snow season and nearly 20% decreases at start of the season, indicating less early-winter accumulation and earlier melt-out. Altogether, these findings highlight a rapid shift toward snow-poor winters in the Var watershed and underscore the increasing vulnerability of Mediterranean Alpine hydrological systems under ongoing climate warming. These resulting snow indicators and trend will be integrated into a decision support system (DSS) to enhance informed and anticipatory water-resources management in the region.
Year: 2026