Assessing the impacts of shoreline hardening on beach response to hurricanes: Saint-Barthélemy, Lesser Antilles

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Sea level rise risks and societal adaptation benefits in low-lying coastal areas

Sea level rise (SLR) will increase adaptation needs along low-lying coasts worldwide. Despite centuries of experience with coastal risk, knowledge about the effectiveness and feasibility of societal adaptation on the scale required in a warmer world remains limited. This paper contrasts end-century SLR risks under two warming and two adaptation scenarios, for four coastal settlement archetypes (Urban Atoll Islands, Arctic Communities, Large Tropical Agricultural Deltas, Resource-Rich Cities). We show that adaptation will be substantially beneficial to the continued habitability of most low-lying settlements over this century, at least until the RCP8.5 median SLR level is reached. However, diverse locations worldwide will experience adaptation limits over the course of this century, indicating situations where even ambitious adaptation cannot sufficiently offset a failure to effectively mitigate greenhouse-gas emissions

Impacts des cyclones Irma, José et Maria (Septembre 2017) sur les systèmes sédimentaires côtiers de l'île de Saint-Barthélemy

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Post-cyclone readjustment of beaches on Saint-Barthélemy Island (Lesser Antilles)

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Human- and climate-driven shoreline changes on a remote mountainous tropical Pacific Island: Tubuai, French Polynesia

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Impacts of category 5 tropical cyclone Fantala (April 2016) on Farquhar Atoll, Seychelles Islands, Indian Ocean

International audienceThis paper provides newinsights on the impacts of a category 5 tropical cyclone on Indian Ocean atoll reef islands.Using multi-date aerial imagery and field observations, the contribution of tropical cyclone Fantala to shorelineand island change, and to sediment production and transport,was assessed on Farquhar Atoll, Seychelles Islands.Results showthat the twolargest islands (N3km2) only suffered limited land loss (−1.19 to−8.35%)while smallislets lost 13.17 to 28.45% of their initial land area. Islands and islets exhibited contrasting responses dependingon their location, topography and vegetation type. Depending on islands, the retreat of the vegetation line occurredeither along all shorelines, or along ocean shoreline only. The structure (wooded vs. grassy) and origin(native vs. introduced) of the vegetation played a major role in island response. Five days after the cyclone,beach width and beach area were multiplied by 1.5 to 10, depending on the setting, and were interpreted asresulting from both sediment reworking and the supply of large amounts of fresh sediments by the reef outerslopes to the island system. Fourth months after the cyclone, extended sheets of loose sediments were still presenton the reef flat and in inter-islet channels and shallow lagoon waters, indicating continuing sediment transferto islands

Leverages and obstacles facing post-cyclone recovery in Saint-Martin, Caribbean: Between the ‘window of opportunity’ and the ‘systemic risk’?

International audienceThe 2017 hurricane season in the Caribbean Basin recorded 18 events (storms and hurricanes), including Category 5 hurricane Irma on which this article focuses. The aim of this study is to analyse the ‘window of opportunity’ of the post-Irma reconstruction in Saint Martin. Located 250 km north of Guadeloupe, Saint Martin is a small bi-national island composed of two entities: Sint Maarten in the south (state of the Kingdom of the Netherlands) and Saint-Martin in the north (French overseas ‘Collectivit ́e’). Our research focuses on the French region, and reconstructions and formalises various attributes, operations and sectors preceding and following the passage of the cyclone. This research highlights twelve key variables distributed within four interdependent spheres (political-administrative, economic and financial, socio-cultural and land-use planning) of Saint-Martin’s vulnerabilities. This is represented and analysed schematically through an ‘influence diagram’ (ID). The research outlines the balancing or reinforcing effects of four major variables of the post-disaster period: state re- engagement, post-disaster price increases, intra-communal solidarity and updating risk prevention plans. It appears that disasters alone cannot be considered as a ‘window of opportunity’ given the weight of pre-existing structures and operating patterns. The case of Saint-Martin illustrates the inertia of a system in the face of a major event, despite strong decisions to implement disaster risk reduction and recovery

Drivers of shoreline change in atoll reef islands of the Tuamotu Archipelago, French Polynesia

International audienceThis paper increases by around 30% the sample of atoll reef islands studied from a shoreline change perspective,and covers an under-studied geographical area, i.e. the French Tuamotu Archipelago. It brings new irrefutableevidences on the persistence of reef islands over the last decades, as 77% of the 111 study islands exhibited arealstability while 15% and 8% showed expansion and contraction, respectively. This paper also addresses a keyresearch gap by interpreting the major local drivers controlling recent shoreline and island change, i.e. tropicalcyclones and seasonal swells, sediment supply by coral reefs and human activities. The 1983 tropical cycloneshad contrasting impacts, depending on the shoreline indicator considered. While they generally caused a markedretreat of the stability line, the base of the beach advanced at some locations, as a result of either sedimentreworking or fresh sediment inputs. The post-cyclone fair weather period was characterised by reversed trendsindicating island morphological readjustment. Cyclonic waves contributed to island upwards growth, whichreached up to 1 m in places, through the transfer of sediments up onto the island surface. However, the steepouter slopes of atolls limited sediment transfers to the reef flat and island system. We found that 57% of the studyislands are disturbed by human activities, including ‘rural’ and uninhabited islands. Twenty-six percent of theseislands have lost the capacity to respond to ocean-climate related pressures, including the ‘capital’ islandsconcentrating atolls' population, infrastructures and economic activities, which is preoccupying under climatechange