Unraveling Drought Patterns and Abrupt Changes in the Western Alps: A Dual Index Approach

Climate change has intensified across Alpine regions, causing significant alterations in precipitation regimes and snowpack levels, with notable implications for ecosystems and water availability both locally and downstream. This study investigates meteorological and hydrological droughts in the western Alps using the Standardized Precipitation Evapotranspiration Index (SPEI) and the Standardized Snowpack Index (SSPI). Drought duration, severity, and inter-index relationships were examined using the Seasonal Kendall (SK) test and the Bayesian Estimator of Abrupt change, Seasonality, and Trend (BEAST) to detect trends, seasonality, and abrupt shifts. The SK test revealed statistically significant decreasing trends across the region. More negative values of the SPEI index over longer timescales indicate worsening hydrological conditions, suggesting potential reductions in water availability and an increased risk of prolonged, severe droughts. Meanwhile, the BEAST analysis identified notable abrupt changes in both SPEI and SSPI, capturing increasing and decreasing shifts. These suggest that, while long-term trends indicate drying conditions, short-term increases likely associated with extreme weather events are also evident. These findings underscore the complexity of hydrological dynamics in the Alps and highlight the necessity for further detailed research to better understand and manage water resources resilience under changing climate conditions.