Future intensification of severe multi-hazard supercells in a semi-arid environment of Southern Europe

Le résumé fourni par la source

Severe convective storms capable of producing extreme surface impacts simultaneously (such as large hailstones, strong winds, and heavy rainfall) present a major challenge to numerical weather prediction and risk assessment. On 6 July 2023, the Ebro Valley (Aragon, Spain) was impacted by a series of two high-impact supercells. The first supercell exhibited an extraordinary multi-hazard nature, producing a 50-km swath of giant hail (≥ 10 cm), a tornado, and a downburst with estimated gusts exceeding 200 km/h. The second supercell triggered flash flooding in the city of Zaragoza (population > 700,000) and large hail (> 5 cm) to the south of the city.This study applies a sub-km-scale pseudo-global warming storyline approach to this compound high-impact event to quantify how anthropogenic climate change will alter its physical drivers and destructive potential. We downscale global climate perspectives to the storm scale by comparing a factual simulation with a future scenario (SSP5-8.5). We perturb initial and boundary conditions using climate change deltas derived from each CMIP6 climate model. We focus on the physical understanding of cascading hazards: specifically, whether future warming enables a transition towards storms that sustain giant hail growth while simultaneously enhancing precipitation efficiency (flash flood risk) and downdraft intensity. Our results aim to demonstrate how event-based storylines can unravel the interactions between thermodynamic changes and storm dynamics, revealing if such unprecedented multi-hazard supercells will become the new reality for extremes in semi-arid regions, thereby amplifying their destructive potential.

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