Episodic coastal hazards associated to sea storms are responsible for sudden and intense changes in coastal morphology. Climate change and local anthropogenic activities such as river regulation and urban growth are raising risk levels in coastal hotspots, like low-lying areas of river deltas. This urges to revise present management strategies to guarantee their future sustainability, demanding a detailed diagnostic of the hazard evolution. In this paper, flooding and erosion under current and future conditions have been assessed at local scale at the urban area of Riumar, a touristic enclave placed at the Ebro Delta (Spain). Process-based models have been used to address the interaction between beach morphology and storm waves, as well as the influence of coastal environment complexity. Storm waves have been propagated with SWAN wave model and have provided the forcings for XBeach, a 2DH hydro-morphodynamic model. Results show that future trends in sea level rise and wave forcing produce non-linear variations of the flooded area and the volume of mobilized sediment resulting from marine storms. In particular, the balance between flooding and sediment transport will shift depending on the relative sea level. Wave induced flooding and long-shore sand transport seem to be diminished in the future, whereas static sea level flooding and cross-shore sediment transport are exacerbated. Therefore, the characterization of tipping points in the coastal response can help to develop robust and adaptive plans to manage climate change impact in sandy wave dominated coasts with a low-lying hinterland and a complex shoreline morphology.

[1] Projected future regional wave climate scenarios at a high temporal-spatial scale were obtained for the NW Mediterranean Sea, using five combinations of regional-global circulation models. Changes in wave variables were analyzed and related to the variations of the forcing wind projections, while also evaluating the evolution of the presence of the different types of sea states. To assess the significance of the changes produced, a bootstrap-based method was proposed, which accounts for the autocorrelation of data and correctly reproduces the extremes. For the mean climate, relative changes of H_s up to ±10% were obtained, whereas they were around ±20% for the extreme climate. In mean terms, variations of H_s are similar to those associated with wind speed but are enhanced/attenuated, respectively, when fetch conditions are favorable/unfavorable. In general, most notable alterations are not in the H_s magnitude but rather in its direction. In this regard, during the winter season, it is interesting to note that the significant deviations between the results derived from the two global circulation models are larger than those between regional models. ECHAM5 simulated an enhanced west wind flow that is translated into more frequent W-NW waves, whereas the HadCM3Q3 global model gives rise to the east component, which contributes to a higher intensity and number of storms coming from such a direction and directly affects the wind-sea/swell distribution of coastal stretches that face east, like the Catalan coast. Different patterns of change were obtained during the summer when a common rise of NE-E waves was found.