University of French Polynesia

Over the past couple of decades, thanks to the sustained development of Global Climate Models (GCMs) combined with dedicated downscaling strategies such as regional climate modelling or statistical downscaling, climate projections and associated services are now increasingly available across many regions, particularly in nations of the Global North like France. However, whereas this is the case for continental France, the country includes numerous overseas territories, most of them being small islands in the tropical Atlantic, Indian and Pacific Oceans, where this information was only partially available until recently, if at all.Here we present the recent development of ensembles of climate projections for most French tropical overseas territories (French West Indies and Guiana, Reunion Island, Mayotte, New Caledonia and French Polynesia), complemented with services in the form of climate information provided for different regional warming levels. The ensembles consist in the blending of data from global climate models (CMIP6), regional climate models (e.g. CORDEX), high-resolution global models and convection-permitting models where available. The models are evaluated against gridded and local observations with a focus on important regional climate processes, and selected accordingly for each domain. Fine-scale reference products for daily surface temperature and precipitation are developed for each territory. They combine long-term weather station observations with high-resolution data from either evaluation simulations driven by the ERA5 reanalysis or numerical weather prediction models. These products are then used to bias-correct and statistically downscale model fields, thereby providing kilometer-scale ensembles of transient climate simulations for each territory over both the historical and future periods, which are made freely available on national climate data portals (DRIAS, Climadiag Commune).In addition, local temperature observations are used to constrain warming projections from CMIP6 for each territory, in order to compute regional warming levels corresponding to global warming levels +1.5°C, +2°C and +3°C. Following the national reference warming trajectory for adaptation to climate change (TRACC), a framework that has been previously applied over continental France to guide adaptation policies, climate indices are computed for these regional warming levels from the aforementioned climate projections and also made freely available. In addition to generic indices (e.g. number of hot days/nights, of heavy precipitation days etc.), tailored indices for the agriculture, water resource, energy, public health and disaster management (wildfires, coastal hazards) sectors are being developed using local impact data from various stakeholders.Future extensions include regional climate model emulators previously developed for European domains. They show encouraging results for tropical islands and are expected to make key contributions to the characterization and understanding of climate projection uncertainties in these data-scarce regions.

Abstract This study investigates the occurrence of surface elevation oscillations, known as seiches, at the atoll scale. We show that the innovative Ka‐band Radar Interferometer (KaRIn) onboard the Surface Water Ocean Topography (SWOT) satellite makes it possible to visualize seiche‐like structures within lagoons of French Polynesia. This ability to capture two‐dimensional sea surface undulations of low amplitude (on the order of a few centimeters) in relatively small water bodies (less than 80 km in length) is unprecedented in satellite altimetry, and opens new avenues of research into these events and their contribution to coastal erosion and flooding. Our study combines sea surface height observations from SWOT with in situ measurements conducted in the Raroia lagoon and theoretical calculations based on an eigenvalue model. These three complementary approaches—satellite remote sensing, in situ data, and theoretical modeling—allow us to investigate both the spatial and spectral properties of seiches in atoll islands.

Area-based conservation is a popular strategy to address biodiversity decline. However, despite the identification of enabling conditions, many initiatives still fail at delivering positive outcomes for nature and people. This study examines how enabling conditions are operationalized and their influence on conservation effectiveness using social-ecological approaches. Guided by the central question of whether the way enabling conditions are put into practice affects conservation outcomes, the study pursues three objectives: (1) to document the processes through which enabling conditions are operationalized, (2) to distinguish the different forms of operationalization, and (3) to assess how these processes influence conservation outcomes, in order to extract lessons that may serve as best practices for future initiatives. By comparing the establishment of two coral reef conservation initiatives in the same region, we identified diverse ways in which enabling conditions are put into practice, providing examples for conservation practitioners. Discourse analysis of stakeholders’ perception highlighted that enabling conditions being in place alone does not guarantee success. Instead, the way they are implemented—through specific action-situations, their interactions, and the stakeholders involved—plays a crucial role in delivering conservation outcomes. Operationalization can have both direct and indirect effects, influencing outcomes at one stage of establishment or at later stages. Sequencing and timing also emerged as critical factors affecting perceptions of benefits, compliance with regulations, and the sustainability of conservation measures. These findings offer practical guidance for decision-makers and managers by illustrating how enabling conditions can be operationalized to support more effective and context-sensitive conservation efforts.

Humid heat stress and heatwaves pose significant risks for living organisms, from humans and wildlife to insects. These threats have wide-ranging health, ecological, and socio-economic impacts that are expected to worsen with climate change. How large-scale climate modes drive the week-to-month variability of humid heat remains poorly understood at the global scale. This limitation hinders the development of accurate forecasts necessary for risk-management measures, notably in the heavily populated and ecologically fragile regions of the tropics and subtropics. With forecast lead times up to several weeks, the Madden-Julian Oscillation (MJO), a global-scale intraseasonal tropical atmospheric disturbance circumnavigating earth in around 30-60 days, provides considerable predictability for weather conditions, and meteorological and oceanic extremes. Here we show that the MJO, and the associated boreal summer intraseasonal oscillation (BSISO), have a significant influence on humid heat and heatwaves over much of the tropics and subtropics across all seasons, both over terrestrial and marine regions. Humid heatwave likelihood can double or halve, depending on the MJO phase, in large areas of the Earth. The MJO/BSISO's influence on wet-bulb temperature is primarily via specific humidity rather than dry-bulb temperature anomalies. In the subtropics and other regions where we typically do not find a strong signal of the convection, we find that intraseasonal anomalies of specific humidity and dry-bulb temperature are influenced by horizontal advection in the planetary boundary layer. Particularly in the subtropics where advection of the climatological moisture and temperature gradient by MJO-related anomalous winds is an important term.

Context Historically, humpback whales migrating past Aotearoa New Zealand (NZ) were linked to western South Pacific wintering grounds and Antarctic feeding grounds. As populations have recovered, research has focused on contemporary connectivity patterns throughout the South Pacific. Aims To determine the contemporary connectivity of winter breeding grounds for humpback whales on their northern and southern migrations past NZ, and those at the Kermadec Islands (Rangitāhua) migratory stopover. Methods We generated DNA profiles (mitochondrial DNA (mtDNA) haplotypes, genetic sex and microsatellite genotypes) using skin samples collected from whales between 1998 and 2021. We used comparisons of DNA profiles and a mixed-stock analysis of mtDNA haplotypes to determine the most likely wintering grounds of genetically identified individuals. Key results DNA profiles of 350 individual whales from NZ were compared to profiles from Oceania (n > 2000), Central and South America (n = 452) and East Australia (n = 809). This comparison revealed 35 genotype matches, mainly to New Caledonia and East Australia. The mixed-stock analysis showed that northbound whales (n = 145) had approximately equal assignment proportions to East Australia and New Caledonia whereas southbound whales (n = 74) showed a two-fold higher assignment to East Australia. In contrast, whales passing Rangitāhua (n = 112) assigned to New Caledonia and other Pacific wintering grounds but not to East Australia. Conclusions Humpback whales passing mainland NZ on their north and southbound migrations are strongly associated with East Australia and New Caledonia wintering grounds. Those migrating south past Rangitāhua have a broader range of wintering ground destinations, including a connection to Central America.