How compound flood drivers have changed over time in the Catalan coast (NW Mediterranean)

This study examines multi-decadal changes in rainfall and wave interactions driving compound flooding along the Catalan coast (NW Mediterranean) from 1950 to 2022. While growing attention has been given to the increasing impacts of coastal storms in the Mediterranean, this work examines whether such changes are linked to variations in the intensity, frequency, or dependence of the underlying hazard drivers. Results show marked temporal and spatial shifts in the dependence structure between rainfall and waves. Initially near-independent, several basins exhibit a progressive strengthening of dependence and upper-tail coupling, indicating growing synchronization between heavy rainfall and energetic wave events, together with an increased probability of extreme rainfall in northern Catalonia. The frequency of extreme compound events has increased in accordance with the strength of dependence. Northern basins exhibit the highest joint probabilities and annual occurrences, while southern basins remain less affected. Synoptic-scale analyses link these trends to a decline in Atlantic Lows and a concurrent rise in Mediterranean Lows and Cut-Off systems, atmospheric configurations conducive to concurrent heavy rainfall and high waves. The observed north-south gradient in compound hazard can be partly explained by the preferential storm tracks affecting the NW Mediterranean. Cyclonic systems typically develop or intensify in the Gulf of Lion and propagate southeastward, generating strong northeasterly winds and intense precipitation along the northern Catalan coast. The results suggest a potential intensification of compound coastal hazards in northern Catalonia and the need to incorporate evolving driver dependence into coastal risk assessment and climate adaptation strategies.