Sources and characteristics of short-duration heavy convective precipitation events in the southeastern Alpine forelands

Severe short-duration thunderstorms are a characteristic part of summer rainfall in the southeastern Alpine forelands. These heavy convective precipitation events (HCPEs) pose a severe risk to the region in the form of flash floods and landslides. Despite their crucial role in summer rainfall and natural hazards, the moisture sources and spatial structure of such HCPEs are still largely unknown.

The presented study links these highly localized events to large-scale processes to identify possible moisture source regions through backward trajectories obtained from Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model runs with ERA5 data. To complement this large-scale analysis, we use high-resolution data from the dense WegenerNet climate station network in southeastern Austria, to investigate the local characteristics and spatial structure of HCPEs.

The combination of large- and local-scale analysis results in a multi-faceted picture of HCPEs and their characteristics. We find that temperature is a key driver of HCPEs and that moisture from the Mediterranean region is a key influencing factor on the occurrence, magnitude, and spatial extent of such events in the study region. Furthermore, we find differences in the storm characteristics depending on the season and region of moisture source.

From a more general perspective, our findings imply that rises in temperature and humidity will likely result in more intense HCPEs with larger spatial extents, which potentially will increase the severity of floods and other natural hazards and hence also the damage risks in the southeastern Alpine forelands.