From giant hail to flash floods: is climate change intensifying extreme convective events in Spain?

Severe convective storms are among the most damaging weather hazards in Spain, often producing extreme precipitation, flash floods, large-to-giant hail, tornadoes and severe convective wind gusts. These hazards are especially relevant in the Mediterranean region, where complex terrain, very warm
sea surface temperatures, strong low-level moisture transport and cut-off lows can interact to promote high-impact events. During the last decades, Spain has experienced several extreme convective episodes with remarkable socio-economic impacts. In addition, our database of large hail events shows an increase in the frequency of large hailstorms, raising the question of whether anthropogenic climate change is already modifying the physical environments in which these hazards develop.

Here, we analyze the role of climate change in recent extreme convective events in Spain using a pseudo global warming storyline approach. High-resolution numerical simulations of observed events are repeated under perturbed thermodynamic conditions representative of different climatic states. This framework allows us to assess how changes in moisture availability, instability, microphysical processes, vertical motions and storm dynamics affect the intensity and destructive potential of highimpact convective storms.

This approach is applied to three recent events with very different surface impacts. The first case study focuses on the giant hailstorm that affected northeastern Spain on 30 August 2022, producing hailstones up to 12 cm in diameter, the largest documented in Spain. Results indicate that the present climate provided a more favourable thermodynamic environment for severe hail than a preindustrial-like climate (Martín et al. 2024), while future warming would further increase the likelihood of very large hailstorms. The second case study examines the catastrophic Valencia flash floods of 29 October 2024, associated with a cut-off low and rainfall accumulations exceeding 300 mm over a broad area and locally reaching 771 mm in 24 h. Storyline simulations show that current anthropogenic climate conditions significantly intensified sub-daily rainfall through amplified storm dynamics, such as stronger vertical motions or enhanced microphysics activity (Calvo-Sancho et al. 2026). The third case study addresses the severe multi-hazard supercell outbreak of 6 July 2023 in the Ebro Valley, where storms produced giant hail, a tornado, destructive downburst winds and flash flooding (Calvo-Sancho et al. 2026).

Overall, these results highlight the growing threat posed by severe convective storms in a warming Mediterranean climate, emphasizing how high-resolution numerical modeling is essential to strengthen adaptation strategies, improve early-warning systems, and reduce societal vulnerability to extreme rainfall, severe hail and compound convective hazards.

References:

Martín, M. L., Calvo-Sancho, C., Taszarek, M., González-Alemán, J. J., Montoro-Mendoza, A., Díaz-Fernández, J., et al. (2024). Major role of marine heatwave and anthropogenic climate change on a Giant hail Event in Spain. Geophysical Research Letters, 51, e2023GL107632. https://doi.org/10.1029/2023GL107632

Calvo-Sancho, C., Díaz-Fernández, J., González-Alemán, J.J. et al. Human-induced climate change amplification on storm dynamics in Valencia’s 2024 catastrophic flash flood. Nat Commun 17, 1492 (2026). https://doi.org/10.1038/s41467-026-68929-9

Calvo-Sancho, C., González-Alemán, J. J., Halifa-Marín, A., Martín, M. L., and Azorin-Molina, C.: Future intensification of severe multi-hazard supercells in a semi-arid environment of Southern Europe, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18069, https://doi.org/10.5194/egusphere-egu26-18069, 2026.