Air temperature and precipitation trends in the Extended European Alpine Region over 1961-2020 from a dense network of surface weather stations

The European Alps and their surroundings (hereby referred to as the Extended European Alpine Region, EEAR) are known to be a hot-spot of climate change as they are experienc-ing a faster warming rate than other regions in the world. However, the complex nature of the Alpine terrain makes it more difficult to understand how climatic changes are distrib-uted over space, and in particular with elevation. In this study, we present a comprehensive analysis of how air temperature, precipitation and a broad set of extreme indices have changed over the EEAR during the period 1961-2020, based on a newly developed daily observational dataset with unprecedented spatial density. The analysis relies on robust trend estimation using the non-parametric Sen's slope method, with statistical significance assessed via the Mann-Kendall test. In addition, elevation-dependent climate change is investigated through a twofold approach that accounts for both linear and non-linear pat-terns. The analysis of the trends of air temperature and precipitation highlights the en-hanced warming in the Alpine region, which amounts to about +2(degrees)C on average during the 1961-2020 period. In terms of temperature extremes, the same period is characterized by a significant increase in warm spells duration index (WSDI), +10.1 days, and in both minimum and maximum temperature indices, respectively +48 warm nights (TN90p) and +49 warm days (TX90p). While mean precipitation does not show a significant change in time, the frequency of extreme rainfall events (R95p index) significantly increased by about +13 days since 1961. Moreover, an enhanced warming with elevation is observed for mean and minimum temperature from February to May, while increasing precipitation trends with elevation are found, mainly in summer.