Modelling hail risk in Europe based on convection-resolving climate simulations: Methods and expected changes in a warming climate

Hail is a severe meteorological hazard that can cause significant damage to infrastructure and agriculture. Studies on expected changes in hail severity in a warming climate and recent record-breaking hail impacts 2022 in France and 2023 in Italy highlight the importance of quantifying hail risk in a changing climate. As part of the Swiss hail research project scClim, we approach this question leveraging the first decadal convection-resolving climate simulations with the integrated hail diagnostic HAILCAST. Following a pseudo-global-warming approach, a present-day scenario with ERA5 boundary conditions from 2011-2021 is compared with a 3°C global warming scenario. We calibrate building vulnerability functions based on >100’000 hail damage reports from four Swiss building insurance companies. The calibrated model highlights the concentration of hail damages into few events with limited spatial extent, which entails a large uncertainty in the climate change signal based on a bootstrap sampling of originally modelled events. Assuming a building vulnerability as calibrated over Switzerland, hail damage potential is expected to increase in over 85% of the European countries within the modelling domain, with decreases primarily concentrated in France and the Iberian Peninsula. While the sampling uncertainty within the 11-year climate simulations clearly exceeds the climate change signal locally, we expect a clear hail damage potential increase of 25-42% aggregated over Europe. Beyond the expected changes in hail damage potential, this contribution highlights methodological aspects and key uncertainties of hail risk quantifications based on climate simulation data. In particular, we discuss the use of spatial resampling of hail swaths to capture worst-case events, the uncertainty in building vulnerability quantification, and the implications of the small spatial scale and local severity of damaging hail streaks.