Sea-level rise is projected to reshape compound flooding potential in microtidal environments along the Spanish Mediterranean coastline

Abstract Compound flooding, arising from the concurrence of extreme rainfall and elevated coastal water levels, poses a growing challenge for climate risk assessment in coastal regions. In microtidal environments, where meteorological forcing dominates coastal water levels, interactions between terrestrial runoff and marine processes can strongly amplify flood impacts. Yet future changes in compound flooding remain poorly constrained, and the relative roles of storm characteristics and sea-level rise are unclear. Here, we develop a multivariate analytical framework that explicitly resolves non-linear interactions between heavy rainfall and coastal water levels by decomposing compound flooding into event intensity, joint occurrence probability, and statistical dependence. Applying this framework along the 1600 km Spanish Mediterranean coastline using a 17-member EURO-CORDEX ensemble under a high-emissions scenario, we show that projected changes in storm characteristics alone lead to generally stable or declining compound flooding potential. In contrast, sea-level rise fundamentally reshapes rainfall-coastal water-level interactions, driving widespread increases in compound flooding potential by 2100. These results identify sea-level rise as the dominant control on future compound flooding in microtidal coastal environments.