Future wave climate in the NW Mediterranean from multi-model CMIP6 wind projections

Coastal areas play a critical role in the well-being of communities worldwide. The Mediterranean basin is a climate change hotspot and contains several vulnerable, low-lying areas such as the Ebro Delta (Northeast Spain). In this study, CMIP6 wind projections from 19 GCMs are used to obtain medium-to-high resolution wave conditions for 2070–2100 in the North-Western Mediterranean, and very-high resolution wave data near the Ebro Delta. The SWAN wave model included in the COAWST modeling suite is used to simulate wave conditions following a nesting approach with three domains (Western Mediterranean, Balearic Sea, Ebro Delta). The model is first validated in the Western Mediterranean by forcing it with ERA5 winds and comparing the results with measurements from seven wave buoys. SWAN model outputs forced with historical GCMs are then evaluated and compared to results from the validation model. Finally, wave conditions are projected under two climate change scenarios, SSP2-4.5 and SSP5-8.5. Evaluation of historical models shows a clear relation between GCM resolution and historical model performance, highlighting the importance of high-resolution wind projections. Wave projections show future decreases in mean and extreme significant wave height, the strongest and most consistent in the Balearic Sea. A general end-of-century reduction in mean significant wave height is detected, with the best-performing models projecting 5-10% reductions at Tarragona buoy, closest to the Ebro Delta. Changes in extremes are more uncertain and heterogeneous, between 10-20%. Overall, this study is novel in its generation of a multi-model wave ensemble using CMIP6 wind projections, sensitivity analysis to domain and wind resolution, and use of model ranking procedures.