Storm Gloria (2020): coexisting types of compound flooding in the West Mediterranean Region
Abstract
Compound flooding arises from the interaction of multiple hydrometeorological drivers, producing impacts that exceed those expected from individual hazards. Although different types of compound events have been widely described, they may also occur simultaneously during exceptional meteorological episodes affecting large regions. Storm Gloria, which struck the Spanish Mediterranean coast between 19 and 25 January 2020, provides a paradigmatic example, as multivariate, spatially compound, and temporarily compound events developed concurrently across the region. The event affected 770 municipalities, caused 14 fatalities and three missing persons and generated about EUR 2022 204 million in Spain's Insurance Compensation (CCS) payouts. The analysis combines daily precipitation ( P 24 h ; 662 AEMET rain gauges), maximum wind gusts (140 AEMET stations), and significant wave height ( H s ; 50 SIMAR/CoExMed points) with municipality-level CCS compensation data associated with floods, windstorms and coastal flooding, respectively. The event window is objectively defined (≥40 mm d −1 at ≥2 stations), and hazard severity is mapped using operational thresholds ( P 24 h =40/100/200 mm; H s =2/5/7 m; wind gusts ≈70/90/100 km h −1 ). The probability of multivariate and spatially compound events was quantified using a two-sided conditional framework and copula models, while the temporally compounding case was assessed empirically from a sequence of heavy-rainfall episodes. The results show that accounting for the dependence between hazards substantially reduces the estimated return periods of multivariate and spatially compound compared with an assumption of independence. Overall, if the spatial distribution of damages is considered throughout the region, the largest compensation values tend to occur where hazard levels are the highest, although exposure (including insurance coverage) and vulnerability modulate the final impacts. In this event, flooding accounts for the largest share of compensation payments. Beyond documenting an exceptional storm, this study demonstrates how different types of compound events can coexist within a single atmospheric episode and presents an integrated framework linking hazard characterisation, joint probability analysis, and observed impacts that can support compound-aware coastal flood risk assessment in Mediterranean and other coastal regions.