Analysis of sub-regional climates in the European Alps based on the EEAR-Clim observational dataset

Giulio Bongiovanni , Alice Crespi, Michael Matiu, Anna Napoli, Bruno Majone, Dino Zardi

The European Alps exhibit a complex geomorphology and undergo the influences of different climate regimes, resulting in high spatial variability of climatic variables and their changes. To provide a detailed analysis of climate regions and climatic changes occurring at a sub-regional scale during the 1961-2020 period, we exploited an updated regionalization of the European Alps that benefits from EEAR-Clim, a new observational daily dataset permitting a robust analysis of local-scale climate features. The regionalization of the European Alps identifies five sub-regions exhibiting distinct climate features: North-West, North-East, South-West, Central-South, South \& South-East (S\&SE). The analysis of average climate conditions highlighted Central-South and S\&SE as the sub-regions experiencing the warmest temperatures and the highest monthly precipitation totals, mostly in spring and autumn, though characterized by a pronounced variability among stations. Conversely, colder temperatures and moderate yet frequent precipitations occurs in northern Alps. Trends of air temperature and precipitation over these sub-regions highlights uneven warming in the Alpine region. North-East, South-West and S\&SE were identified as the fastest warming sub-regions, with increases over 1961-2020 reaching +2.0°C for minimum temperature, +2.8°C (SW) and +2.4°C (NE and S\&SE) for maximum temperature, respectively. Despite the high spatial and temporal variability of precipitation over the European Alps, the S\&SE sub-region exhibits drying conditions in spring and summer compared to the other regions. Trends in extreme precipitation are more statistically significant compared to changes in mean values, resulting in an increased frequency since 1961 of very extreme rainfall events, mostly in the southern Alps (+18 days). The new regionalization of the European Alps presented here is expected to support a range of climate related applications including impact studies. Moreover, it demonstrates the importance of considering variations in both average climate conditions and ongoing trends across different parts of the Alps, helping to identify areas most vulnerable to the effects of climate change.