Climate change-driven shoreline change along the Catalan coast (NW Mediterranean): A probabilistic approach for risk-informed coastal management

This study quantifies shoreline retreat for multiple sea-level rise (SLR) projections at two contrasting sites along the Spanish Mediterranean coast: the Llobregat delta and Maresme beaches. The Llobregat delta comprises mildly sloped dissipative beaches, while the Maresme coast is characterized by steeper coarse-sediment beaches. Using the probabilistic PCR model, which incorporates both the effects of the long-term wave climate and Sea level rise, we evaluate site-specific responses and compare outcomes with the widely used Bruun rule. The Bruun rule overestimates retreat by up to 70% at Llobregat compared to PCR projections under the SSP5-8.5 scenario. At the same time, the results of the two approaches converge at Maresme for both SSPs considered, both at 2050 and 2100. Thus, the discrepancies between the two approaches appear to be larger at sites with milder slopes. The PCR model projects an accelerating retreat from mid-century, reflecting strong nonlinear interactions between future hydrodynamic forcing and storm erosion. These findings underscore the potential pitfalls of relying solely on Bruun rule derived projections for local scale coastal adaptation planning. Moreover, they highlight how PCR model derived physics based, probabilistic projections of shoreline retreat could lead to more informed and effective decisions on local scale adaptation along vulnerable coastlines.