Anthropogenic climate change intensifies rainfall in extreme compound rainfall-wave events in the NW Mediterranean

The concurrent occurrence of extreme rainfall and energetic wave conditions can generate compound coastal hazards with impacts exceeding those produced by either driver alone. Although recent studies have identified changes in rainfall-wave extremes along the northwestern Mediterranean coast, whether these changes can be attributed to anthropogenic climate remains unclear. Here, we investigate the anthropogenic influence on compound rainfall-wave extremes using five initial-condition ensemble members of the CMIP6 MRI-ESM2.0 model from the Detection and Attribution Model Intercomparison Project, comparing factual (ALL) and counterfactual (NAT) experiments over 1961-2020. Changes in dependence and joint return periods are assessed using Kendall's τ-b and copula-based analyses. No robust anthropogenic signal is detected in the observed strengthening of rainfall-wave dependence, as neither its temporal evolution nor the change in dependence structure identified in ERA5 is consistently reproduced across the ensemble. In contrast, the ALL-NAT comparison suggests an anthropogenic contribution to rainfall intensification in the most extreme compound events, while wave changes remain small and variable across realizations. For example, fitted estimates associate a rainfall-wave combination of P24h ≈ 320 mm and Hs ≈ 4 m with joint return periods of approximately 50 years under NAT and 25 years under ALL. This comparison is indicative, with its magnitude subject to uncertainties in event sampling, marginal fitting, and copula estimation that have yet to be quantified. Agreement with ERA5 supports the model’s representation of baseline characteristics, although further evaluation would strengthen confidence in its response to external forcing. Overall, the findings suggest rainfall intensification within the model framework, while the associated frequency change should be interpreted with caution.