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Atoll islands face increasing coastal risks (coastal erosion and marine flooding) due to climate change, especially sea-level rise. To face increasing coastal risks, various adaptation options are considered by atoll countries and territories, including in particular hard protection (preferred option to date), Nature-based Solutions (increasingly used) and island raising (considered a longer-term solution and a potential alternative to international migration, e.g. in the Maldives). Internal relocation within the same atoll island or atoll, which refers to long-term community movement from one threatened island area or island to a safer island area or island, has previously been disregarded by scholars as a potentially relevant climate adaptation strategy. However, in low-lying coastal areas, it offers real potential to address the dual context of increasing climate risks and the shrinking of the solution space. This paper assesses the potential of internal relocation for atolls by applying to Rangiroa Atoll, French Polynesia, Central Pacific, a two-fold assessment framework questioning its physical relevance ( are some islands high enough to host settlements in the future?) and its societal feasibility ( are the political-institutional and socio-economic conditions in place? Are people willing to relocate ?). The findings show that internal relocation is both relevant and feasible on Rangiroa Atoll and should therefore serve as a pillar to develop robust in situ adaptation pathways in this atoll.

Volto, N. and Duvat, V.K.E., 2020. Applying directional filters to satellite imagery for the assessment of tropical cyclone impacts on Atoll Islands. Journal of Coastal Research, 36(4), 732–740. Coconut Creek (Florida), ISSN 0749-0208. This paper highlights the major insights provided by directional filters using ENVI® software for detecting and mapping cyclone-generated accretional features and analyzing postcyclone sediment reworking. It relies on the study of the impacts of category 5 tropical cyclone Fantala (April 2016) on Farquhar Atoll, Seychelles Islands. Using directional filters first allowed the detecting and mapping of terrestrial (sediment sheets, sediment lobes) and intertidal (shingle and rubble tongues, sediment sheets, sandbars) depositional features. It also helped with highlighting spatial-temporal variations in the postcyclone reorganization of reef flat deposits. One year after the cyclone, along the rectilinear shoreline of elongate islands (i.e. North Island and South Island), massive reef-to-island sediment transfer had already caused the dismantling of cyclone-generated features and beach readjustment; however, in places, newly formed cyclone features exhibited limited dismantling. In contrast, at the island tips, the reworking of postcyclone sediment deposits was still ongoing, explaining still rather limited beach readjustment. The results advocate for the use of remote sensing techniques that complement fieldwork and multidate shoreline change assessment to promote more comprehensive analyses of tropical cyclones' impacts.

Understanding past and present hydrosystem feedbacks to global ocean–atmospheric interactions represents one of the main challenges to preventing droughts, extreme events, and related human catastrophes in the face of global warming, especially in arid and semiarid environments. In eastern Africa, the El Niño–Southern Oscillation (ENSO) was identified as one of the primary drivers of precipitation variability affecting water availability. However, the northern East African Rift System (EARS) still suffers from the underrepresentation of predictive and ENSO teleconnection models because of the scarcity of local to regional historical or palaeo-data. In this paper, we provide a 50-year seasonal flood and drought chronicle of the Awash River catchment from the study of laminated sediment from Gemeri and Afambo lakes (central Afar region, Ethiopia) with the aim of reconstructing the magnitude of regional hydroclimatic events. Pluricentimetric micro-laminated lithogenic facies alternating with plurimillimetric carbonate-enriched facies are investigated in both lakes. We couple dating methods including radiocarbon, short-lived radionuclides, palaeomagnetic field variations, and varve counting on both lake deposits to build a high-resolution age model and to discuss the regional hydrosedimentary dynamics of the Awash River over the last ∼ 700 years with a focus on the last 50 years. Using a multiproxy approach, we observe that following a multicentennial enhanced hydrological period, the two lakes have experienced a gradual decrease in river load inflow since 1979 CE, attaining extreme drought and high evaporative conditions between 1991 and 1997 CE. In 2014, the construction of a dam and increased agricultural water management in the lower Awash River plain impacted the erodibility of local soils and the hydrosedimentary balance of the lake basins, as evidenced by a disproportionate sediment accumulation rate. Comparison of our quantitative reconstruction with (i) lake water surface evolution, (ii) the interannual Awash River flow rates, and (iii) the El Niño 3.4 model highlights the intermittent connections between ENSO sea surface temperature anomalies, regional droughts, and hydrological conditions in the northern EARS.