Assessing coastal vulnerability to climate change at regional scales is now mandatory in France since the adoption of recent laws to support adaptation to climate change. However, there is presently no commonly recognised method to assess accurately how sea level rise will modify coastal processes in the coming decades. Therefore, many assessments of the physical component of coastal vulnerability are presently based on a combined use of data (e.g. digital elevation models, historical shoreline and coastal geomorphology datasets), simple models and expert opinion. In this study, we assess the applicability and usefulness of a multi-criteria decision-mapping method (the analytical hierarchy process, AHP) to map physical coastal vulnerability to erosion and flooding in a structured way. We apply the method in two regions of France: the coastal zones of Languedoc-Roussillon (north-western Mediterranean, France) and the island of La Réunion (south-western Indian Ocean), notably using the regional geological maps. As expected, the results show not only the greater vulnerability of sand spits, estuaries and low-lying areas near to coastal lagoons in both regions, but also that of a thin strip of erodible cliffs exposed to waves in La Réunion. Despite gaps in knowledge and data, the method is found to provide a flexible and transportable framework to represent and aggregate existing knowledge and to support long-term coastal zone planning through the integration of such studies into existing adaptation schemes.

Le Cozannet, G., Garcin, M., Petitjean, L., Cazenave, A., Becker, M., Meyssignac, B., Walker, P., Devilliers, C., Le Brun, O., , Lecacheux, S., Baills, A., Bulteau, T. Yates, M., and Wöppelmann, G., 2013. Exploring the relation between sea level rise and shoreline erosion using sea level reconstructions: an example in French Polynesia. The climate component of sea level variation displays significant spatial variability, and it is now possible to reconstruct how sea level varied globally and regionally over the past half century. The fact that sea level rose faster than the global mean since 1950 in the central Pacific stimulated a study of decadal shoreline changes in this region. Here, the study of Yates et al. (2013) was extended to two additional atolls (17 islets): Tetiaroa and Tupai in the Society islands. Both atolls remain stable on the whole from 1955 to 2001/02, however with significant differences in shoreline changes among their islets and within the period. A modeling of waves genera...

Given recent scientific advances, coastal flooding events can be properly modelled. Nevertheless, such models are computationally expensive (requiring many hours), which prevents their use for forecasting and warning. In addition, there is a gap between the model outputs and information actually needed by decision makers. The present work aims to develop and test a method capable of forecasting coastal flood information adapted to users’ needs. The method must be robust and fast and must integrate the complexity of coastal flood processes. The explored solution relies on metamodels, i.e., mathematical functions that precisely and efficiently (within minutes) estimate the results that would provide the numerical model. While the principle of relying on metamodel solutions is not new, the originality of the present work is to tackle and validate the entire process from the identification of user needs to the establishment and validation of the rapid forecast and early warning system (FEWS) while relying on numerical modelling, metamodelling, the development of indicators, and information technologies. The development and validation are performed at the study site of Gâvres (France). This site is subject to wave overtopping, so the numerical phase-resolving SWASH model is used to build the learning dataset required for the metamodel setup. Gaussian process- and random forest classifier-based metamodels are used and post-processed to estimate 14 indicators of interest for FEWS users. These metamodelling and post-processing schemes are implemented in an FEWS prototype, which is employed by local users and exhibits good warning skills during the validation period. Based on this experience, we provide recommendations for the improvement and/or application of this methodology and individual steps to other sites.

Garcin, M., Baills. A., Le Cozannet, G., Bulteau, T., Auboin, A-L., Sauter, J., 2013. Pluri-decadal impact of mining activities on coastline mobility of estuaries of New Caledonia (South Pacific) This work aims at analysing the relative impact of sedimentary supply by rivers versus the effect of sea level rise and other processes over the last 5 decades of some representative coastal stretches of New Caledonia (South Pacific Ocean). The study of twelve coastal estuarine stretches has shown erosion rates ranging from −1.8m/y to accretion rates up to 5.5m/y over the last 50 years. During this time, the climate component of sea level rise has been evaluated around 0.5mm/y in Nouméa and can be considered identical on the studied island. Vertical movements affecting New Caledonia are suspected to be different between western and eastern parts of the island. Nevertheless, in areas with homogeneous vertical movement, the coastal stretches studied show various evolution rates. The analysis of accreting e...