A systemic and comprehensive assessment of coastal hazard changes: method and application to France and its overseas territories

Abstract

Abstract. In the context of climate change, height and frequency variations of extreme sea levels (ESL) are studied using deterministic and probabilistic approaches. However, this type of approach does not highlight the dynamic effects (waves, currents) generated by meteocean events, beyond their effects on sea-levels. In particular, ESL estimates are certainly calculated by considering the main determining physical factors but cannot report on all the effects of these factors. Ultimately, this can lead to confusion between ESL and hazard. This article proposes a systemic assessment method to analyze coastal hazard changes at regional scales, integrating parameters influencing sea-levels, as well as factors describing the geomorphological context (length and shape of the coast, width of the continental shelf), meteocean events (storms, cyclones and tsunamis), and the marine environment (e.g., coral reef state and sea ice extent). French mainland and overseas territories were selected to apply the method. We have thus highlighted the need to study not only the sea-level variability, but also the current and future characteristics of meteocean events. The long, concave coasts bordered by a wide continental shelf appear particularly sensitive to variations in the intensity or trajectory of meteocean events. Coral reef degradation in the tropics and the decrease in seasonal sea ice extent in the polar regions can also significantly change the nearshore hydrodynamics and impacts on the shoreline. These results help to predict the types of hazard (shoreline erosion, rapid submersion and/or permanent flooding) that will increase the most in different coastal zones.