Identifying Hotspots of Convective Events in the European Alps by Analyzing Synoptic Circulation Types and Report Data of the last 33 Years

Convective events are characterized by extreme precipitation, wind, lightning, and hail. They account for a significant portion of insured natural hazard damages, particularly affecting the agricultural, vehicle, and building sectors. Convective events are expected to intensify with global warming and in recent years, record-breaking hailstone sizes, substantial damage costs, and prolonged, intense convective storms have been observed in Europe. Recent climatological studies of hail and lightning identify the Alpine region as a hotspot of convective activity in Europe (e.g., Fischer et al. 2024). The complex topography of mountain ridges and valleys interacts with the large-scale atmospheric flow, leading to some of the most intensive convective events in Europe. This study aims at a comprehensive analysis of identified hotspot regions across multiple Alpine countries and for different convective hazard types, assessing associated synoptic- to meso-scale environments, their spatio-temporal variability, and the underlying processes. In a first attempt to link large scale atmospheric patterns to regional convective hotspots, we present synoptic circulation types (CTs) of the last 33 years, that show heightened convective activity indicated through clusters of reports in the European Severe Weather Database (ESWD) (Dotzek et al. 2009). The CTs were classified with the cost733class 1.4 software (Philipp et al. 2014) and ERA5 reanalysis data (Hersbach et al. 2020). Additionally, ERA5 environments at the report locations were analyzed considering various environmental parameters. First results show differing and distinct CTs for, e.g., large hail events north and south of the Alps. The 500 hPa geopotential height patterns indicate implications of upstream trough and downstream ridge locations on hail-prone regions. Summertime convective CTs show positive anomalies of specific humidity at 850 hPa and sea surface temperatures, while mean sea level pressure anomalies are comparatively weak. Identifying which synoptic environments favor convective activity at distinct regional hotspots could improve forecasts and risk assessments and so help to reduce the impacts of extreme events around the European Alps.