Abstract. A modelling chain was implemented in order to propose a realistic appraisal of the risk in coastal areas affected by overflowing as well as overtopping processes. Simulations are performed through a nested downscaling strategy from regional to local scale at high spatial resolution with explicit buildings, urban structures such as sea front walls and hydraulic structures liable to affect the propagation of water in urban areas. Validation of the model performance is based on hard and soft available data analysis and conversion of qualitative to quantitative information to reconstruct the area affected by flooding and the succession of events during two recent storms. Two joint probability approaches (joint exceedance contour and environmental contour) are used to define 100-year offshore conditions scenarios and to investigate the flood response to each scenario in terms of (1) maximum spatial extent of flooded areas, (2) volumes of water propagation inland and (3) water level in flooded areas. Scenarios of sea level rise are also considered in order to evaluate the potential hazard evolution. Our simulations show that for a maximising 100-year hazard scenario, for the municipality as a whole, 38 % of the affected zones are prone to overflow flooding and 62 % to flooding by propagation of overtopping water volume along the seafront. Results also reveal that for the two kinds of statistic scenarios a difference of about 5 % in the forcing conditions (water level, wave height and period) can produce significant differences in terms of flooding like +13.5 % of water volumes propagating inland or +11.3 % of affected surfaces. In some areas, flood response appears to be very sensitive to the chosen scenario with differences of 0.3 to 0.5 m in water level. The developed approach enables one to frame the 100-year hazard and to characterize spatially the robustness or the uncertainty over the results. Considering a 100-year scenario with mean sea level rise (0.6 m), hazard characteristics are dramatically changed with an evolution of the overtopping / overflowing process ratio and an increase of a factor 4.84 in volumes of water propagating inland and 3.47 in flooded surfaces.

Background: Climate change and rising sea level will certainly lead to significant changes in the management of low-lying coastal areas in the coming decades. While the most recent studies in the field of coastal storms-related flooding are increasingly integrated, simultaneously addressing hazards and vulnerability, as well as population risk perception, there is still little work to consider the preparedness of stakeholders to manage crises whose frequency and intensity are likely to increase in the next years. Methods: The aim of this paper is to expose the major results of the CRISSIS research program, which proposed a multidisciplinary approach to the management of coastal flood risk in a town particularly exposed on the French Mediterranean coast. The originality of the project was to offer both an integrated approach to risk by analysing its 3 dimensions (hazard, impact and vulnerability, and representations and perceptions held by populations and stakeholders, or « risk culture ») and a very operational section focused on the evaluation of crisis management measures led by local stakeholders. To achieve this objective, two crisis exercises were organized, the first one to test the assimilation by the municipality staff of existing crisis management procedures and the second to allow local actors to integrate in their crisis management procedures the new risk knowledge data issued from research conducted under the program. Results: The project has had three main features; (i) it accurately mapped the submersible areas that present a critical vulnerability, both material and human; (ii) it revelated the poor social representation of marine submersion risk, as well as the obvious lack of awareness of crisis management systems and tools and the behavior to adopt in the event of flooding; (iii) Finally, it highlighted the need, through the crisis exercises, for a better assimilation by the municipality staff of the crisis management procedures defined in the Municipal Rescue Plan. Conclusion: The CRISSIS project has demonstrated the usefulness of an integrated and operational approach of coastal flood risk, not only in terms of studying hazards, stakes and vulnerability, but also in terms of crisis management, in particular through the organisation of crisis simulation exercises.

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