Global Warming Influence on a Giant Hailstorm in Spain via the Pseudo-Global Warming Approach

On August 30^th, 2022, a giant hailstorm with hailstones reaching up to 12 cm occurred in the northeastern Spain. This Spanish giant hailstorm record event caused, in addition to the damage to roofs, cars, and croplands, 67 injuries and even one fatality. During the event, the weather pattern over Europe was a quasi-omega block in the Western Mediterranean with a narrow cut-off low over the center-eastern of France, inducing the development of a very short-wave trough in extreme northeastern Spain. Such setup, the typical summer thermal-low and very high Mediterranean SSTs, promoted vorticity advection and a high amount of moisture in low-levels.

In this study, the climate change effect in the hail-favorable environment, in which hailstone growth was promoted, is analyzed by applying the Pseudo-Global Warming Approach (PGWA). The PGWA is also applied to study the response to global warming during the last part of the 21^st century to the giant hailstorm development. Three climatic models from the CMIP6 (EC-EARTH3, CESM-WACCM, and MRI-ESM2-0) and the PiClim, historical, and SSP5-8.5 scenarios are used to obtain the climate change increment [PRESENT - PiClim and FUTURE-PRESENT) needed in the PGWA. The increments are computed for all the prognostic variables and added to ERA5 to be used as initial/boundary conditions in the simulations obtained from the WRF-ARW model. A control simulation is performed using the ERA5 initial conditions without perturbation to compare it with the preindustrial-like and the future-like climates. 

The results in this first climate change attribution study to giant hailstorms indicate that the environment in a preindustrial-like climate would have been less conducive to convective hazards with a significant reduction in the studied thermodynamic parameters. The hailstorm event considering the preindustrial-like climate would have been less severe than the real event in the present climate. Considering a future-like climate, the results also indicate an enhancement in the thermodynamic variables. Large amounts of instability would be available in the scenario used, exceeding the values of the actual event. Although the hailstone diameter would not increase, the probability of very large hailstone events would increase by ~30%. Therefore, very large hail events would be more likely in hail-favorable supercells at the end of the century.

The use of the PGWA in high-impact severe weather events allows for a better understanding of how these events could change with global warming. This knowledge could help to improve the present early-warnings systems.