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A tool to evaluate the extreme vulnerability of human exposure to sea-floodrisksAxel CreachLaboratory LETG Nantes-Géolittomer (UMR 6554 CNRS and University of Nantes), Campus Tertre BP 81227, 44312 NantesCedex 3, FranceAxel.Creach@univ-nantes.frAbstractThe storm Xynthia hit the west coast of France in February 2010, particularly the areas of Vendée and Charente-Maritime. Xynthia was responsible for the death by drowning of 41 people, after the flooding of coastal areas by thesea (Vinet et al., 2012b). This violent storm was generated by a rare combination of different natural factors. Nevertheless,the number of deaths cannot only be explained by the storm as human exposure to coastal areas was also animportant factor.The aim of this paper is to present a tool to evaluate human exposure and vulnerability to sea-flood risk. The tooltakes the form of an index, which is based on the more important factors of vulnerability (flood level, architecturaltype, dike proximity, accessibility to rescue). It is applied at micro-scale i.e. residential houses. The goal is to proposean easy-to-use tool for decision-makers.IntroductionIn February 2010, the storm Xynthia hit the west coast of France, particularly the areas of Vendée and Charente-Maritime. It was one of the most deadly natural events that the French territory had experienced in recent decades. Itwas responsible for the drowning of 41 people due to the flooding of low lands by the sea (Vinet et al., 2012b).Xynthia was generated by a rare combination of different factors, including high wind speed, high tidal level, andlow pressure, although these were not exceptional in themselves (Feuillet et al., 2012). However, the fact that thestorm crossed over lowland territories produced a large sea surge, which extended the flooding to urban zones. Nevertheless,the number of deaths cannot only be explained by the storm; human exposure to coastal areas was also animportant factor.This exposure is due to the evolution of society and to political choices: coastal areas have become attractive fortourism. This phenomenon is responsible for the development of many residential areas, increasing the pressure onunoccupied areas in coastal towns. In order to meet the new demand, many low lands formerly used for agriculturehave been urbanized (Chauvet and Renard, 1978; Chauveau et al., 2011). These areas are often located behindcoastal dikes. Moreover, many buildings have been constructed according to a traditional architecture, which is notadapted to flooding. These factors have led to significant vulnerability (Vinet et al., 2012a).On the grounds of public safety, former French President Nicolas Sarkozy decided to destroy those houses“where there is a risk of death”. In these so-called “black zones”, houses were bought by the French Administrationand destroyed. 1574 buildings were concerned, mainly in areas where people had died (Mercier and Chadenas,2012). Some criteria were defined to locate those houses to be destroyed, but the speed of the operation led to angerand incomprehension among people. In fact, the “black zones” are a way of identifying very high vulnerability tosea-flood risk.MethodologyHowever, this was a post-event analysis. Following this approach, we wanted to make a prospective evaluation toidentify where there is a risk of death because what happened in Vendée and Charente-Maritime is liable to occur inother areas of the French Atlantic coast which are also concerned with low-lying urbanization. The idea is to buildan easy-to-use tool which can be widely applied to evaluate vulnerability and become an assessment tool for decisionmakers in order to reduce vulnerability. More generally, the expected goal is to locate potential “black zones”.199