Co-occurrence of large hail and heatwaves in European regions in current and future climate scenarios

Large hail and heatwaves are among the most extreme weather phenomena, posing serious risks to human health, ecosystems, and infrastructure, while also leading to significant economic losses. However, the co-occurrence of large hail and heatwaves, and the potential physical mechanisms linking these two phenomena, remain poorly understood. In this study, we investigate the climatology of large hail and the atmospheric drivers of large hail and heatwave co-occurrences across selected European regions, using an 11-year convection-permitting climate simulation with the COSMO regional climate model (2011–2021). In addition, we assess how these extremes may evolve under future climate conditions (+3°C global warming).

Results show increases in large hail frequency across Europe in a warmer climate. In central and eastern regions, the frequency rises approximately 20 %, whereas in the Alpine, Mediterranean, and Baltic regions it nearly doubles. Exceptions are France and Spain, where large-hail frequency declines by 26% and 33%, respectively. Also, there is a notable correlation between the occurrence of heatwaves and large hail across central and eastern Europe.  This relationship is less evident in southern Europe, due to large hail occurs mainly in autumn storms caused by large-scale disturbances. Additionally, large hail during heatwave days is forms in environments with higher median values of most-unstable convective available potential energy and 2 m temperature than large hail in the absence of heatwaves. A spatiotemporal analysis revealed that the days leading up to large hail events increasingly coincide with heatwave conditions. In the present climate, large hail is most often found within ~500 km of heatwave boundaries, both inside and outside them. The future climate scenario indicates a spatial shift of large hail events beyond the heatwave extent across all continental domains.