HAL Collection UNC (Univ. de la Nouvelle Calédonie)
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Nage au-dessus des habitats sous-marins
No full textEn matière d'observation de l'environnement, les données manquent souvent. Mieux suivre la variabilité des habitats de faibles profondeurs océaniques, comme les récifs coralliens ou les herbiers, est un enjeu important pour évaluer la santé des écosystèmes côtiers
Severe Impacts on Water Resources Projected for the Mediterranean Basin
No full textInternational audienceABSTRACT Water resources are becoming increasingly scarce in the Mediterranean Basin due to climate change. Through a systematic review of 262 catchment‐based Mediterranean studies, we provide improved and detailed indications that runoff is projected to decrease by 19%, with increasing severity towards the end of the century and with increasing emission scenarios (up to −39%). We also show negative consequences for other water resources (soil moisture, aquifer recharge, irrigation demand), hydrological extremes (low flows), and water and soil quality (nutrient concentration, soil salinity, soil erosion), with negative impacts on rainfed and irrigated agriculture in the Mediterranean Basin. To protect water security, climate change adaptation aiming at more efficient water use and water retention in soils will be needed. While these adaptation measures have the potential to reverse the impacts of climate change, they may reduce downstream water availability and may be insufficient under extreme climate conditions
Evolution of flood generating processes under climate change in France
No full textInternational audienceAbstract. The impact of climate change on floods varies across regions, and observed trends in flood characteristics are often explained by differential changes in the processes that cause flooding. This study explores changes in flood magnitude and flood-generating processes under different climate change scenarios for a large number of basins in France. It is based on an unprecedented exercise to model the impacts of climate change on hydrology, using a semi-distributed model (GRSD) applied to 3727 basins with 22 Euro-CORDEX bias-corrected climate projections using two greenhouse gas emission scenarios (RCP4.5 and RCP8.5). Annual maxima of daily simulated streamflow were extracted for the period 1975–2100, resulting in a set of over 10 million flood events, and a trend analysis was carried out on both flood magnitudes and flood generating processes. Increasing trends in flood magnitudes are only found in the northern regions of France, although multi-model convergence rarely exceeds 60 %. The highest increases are observed for the 20 year floods and under the RCP8.5 scenario. A classification of floods according to their generating process revealed that floods linked to soil saturation represent more than half of all floods in France. The relative change in the importance of the different flood-generating processes is not spatially homogeneous and varies by region. The proportion of floods linked to soil saturation excess is increasing in the temperate and continental climate zones in the Northeast, while decreasing in the southern Mediterranean regions. In these Mediterranean regions, the proportion of floods linked to infiltration excess related to extreme rainfall is increasing. Both the frequency and magnitude of floods linked to snowmelt processes are decreasing in mountainous areas. On the contrary, the most extreme floods associated with rainfall on dry soils tend to increase, in line with the increase of rainfall intensity. Overall, trends in antecedent soil moisture conditions are as important as trends in intense rainfall to explain flood hazard trends in the different climate projections. This study shows how important it is to decipher the changes in the different flood generating processes in order to better understand their evolution in different hydroclimatic regions
Les risques naturels côtiers et l’adaptation au changement climatique à Mayotte : de l’ingénierie côtière à l’ingénierie sociale, quelles perspectives ?
No full textPrésentation dans le cadre du séminaire "Les risques naturels à Mayotte et le secteur associatif" organisé par le réseau EEDD 976, Barakani, Mayott
High-resolution species distribution modelling of two coastal biogenic habitat-forming species in an Ecologically and Biologically Significant Area of the Bay of Fundy, Canada
No full textInternational audienceHigh-resolution species distribution models (SDMs) were developed for two benthic invertebrate species of marine conservation significance across a 113 km2 Ecologically and Biologically Significant Area (EBSA) of the Bay of Fundy, Canada. The stalked tunicate, Boltenia ovifera, and horse mussel, Modiolus modiolus, can form coastal biogenic habitat and are vulnerable to disturbance. A near-seabed imaging survey (depths ranging from 8 to 79 m) provided presence, absence, and abundance data for both species. Boosted Regression Tree SDMs combined these data with 11 environmental variables. Presence-probability distributions were generated; however, abundance patterns could not be adequately modelled. Oblique geographic coordinates, which incorporate location of samples as information, proved useful for predicting species presence, along with seabed rugosity, maximum current speed and bathymetry for B. ovifera, and maximum and minimum current speed along with seabed rugosity for M. modiolus. High-resolution SDMs (in this case, 5-m grid) provide enhanced spatial context for ocean managers towards marine spatial planning in high-use coastal marine environments where bottom contact fisheries access and other coastal development must be balanced against marine conservation objectives
Vulnerability of Coral Reefs to Contaminants of Emerging Concern
No full textInternational audienceCoral reefs are highly vulnerable to contaminants of emerging concern (CECs), posing substantial threats to their sustainability within the context of global climate change. This chapter focuses on three major classes of CECs: micro-nanoplastics (MNPs), persistent organic pollutants (POPs), and trace metallic elements (TMEs). It provides an overview of their occurrence in coral reefs across the Pacific, Atlantic, and Indian Oceans, along with their potential impacts on key organisms such as corals and fish. Drawing upon insights from both laboratory and field investigations, we assess existing research gaps and explore new prospects for effective risk management strategies. The contamination of coral reefs by these pollutants, driven by a combination of local and global anthropogenic pressures, can impair marine species at multiple biological levels. Moreover, their simultaneous presence may amplify ecological disruptions, affecting primary production and reef ecosystem functioning. Given the complexity of these interactions, additional research is required to better understand the fate, transport, and synergistic effects of these contaminants in reef environments. Such efforts are crucial to improve exposure assessments, refine conservation strategies, and develop targeted mitigation measures. Addressing these challenges requires interdisciplinary collaboration, standardized monitoring protocols, and cooperation among research institutions to ensure the long-term resilience of coral reef ecosystems worldwide
Dynamics of Infragravity Waves Across the Southern Reef Barrier of Mayotte, Indian Ocean
No full textInternational audienceDue to climate change, tropical islands are being increasingly exposed to coastal hazards. Under energetic incident swells, infragravity (IG) waves can have a key contribution to extreme water levels and flooding, but their dynamics at barrier reef remains little studied. In this context, this study analyses IG wave generation mechanisms and transformations across a barrier reef to the southwest of Mayotte (Indian Ocean), combining a new comprehensive field dataset with phase resolving wave modelling. This analysis reveals that IG waves are mostly breakpoint-forced and suffer a substantial dissipation by bottom friction, particularly at low tide. Numerical experiments with reduced bottom friction representing a degraded coral reef suggest that IG waves would grow by about 20% across the reef at high tide. This study highlights the key role of coral reefs to dissipate IG waves and hence limit extreme water levels and subsequent coastal hazards.</div
Le faaapu : prendre soin de sa terre, prendre soin de soi.: Le jardinage comme stratégie de « résistance par la subsistance »
No full textInternational audienceLes îles du Pacifique et notamment la Polynésie française ont régulièrement été confrontées à des perturbations environnementales causées par des événements météorologiques parfois violents. Les agriculteurs et habitants qui cultivent des produits alimentaires sont particulièrement exposés à ces évènements et ont déployé une « culture du risque » (David 2004; Magnan, Duvat, et Garnier 2012). Par exemple, ils ont développé certains pratiques d’adaptation aux effets du changement climatique (paillage, variation des types de cultures et de plantation…), notamment par l’hybridation des savoirs (savoirs transmis, savoirs institutionnels, savoirs enseignés…). Ce sont particulièrement ces savoirs locaux et leur hybridation et circulation que nous étudions dans le cadre du projet CLIPSSA (Climat du Pacifique, Savoirs locaux et Stratégies d’Adaptation). A cette fin, notre équipe composée d’anthropologues, ethnoécologues, géographes et agronomes (chercheurs et stagiaires) a mené 57 entretiens avec des agriculteurs de Tahiti et de Moorea entre 2024 et 2025, dont une trentaine cultivent à une petite échelle (quelques dizaines de m2).Les adaptations au changement climatique sont largement répandues mais diffèrent grandement d’un type de production à un autre. Les problématiques météorologiques rencontrées (vents, sécheresse, fortes pluies…), les enjeux de la production (produire pour se nourrir, pour avoir un revenu…) ou encore les ressources mobilisées (réseau familial, professionnel, niveau d’équipement, capacité d’investissement…) ne sont pas les mêmes pour une personne qui cultive du vivrier et du maraichage sur quelques dizaines de m2 que pour un agriculteur qui combine maraichage, arboriculture et élevage sur plusieurs hectares. Nous proposons dans le cadre du colloque « l’alimentation en Océanie » d'interroger les différentes fonctions nourricières des faaapu (jardins potagers) de Tahiti et de Moorea, en considérant tant les dimensions alimentaires, que celles sociales, culturelles et spirituelles. Le faaapu est en effet au cœur de stratégies économiques de sobriété des habitants, visant d’abord à réduire les dépenses alimentaires. Mais nous verrons également que les faaapu occupent de nombreuses fonctions : sociale (créer du lien, échanger avec sa famille, ses amis), esthétique (embellir son environnement domestique), de loisir voire de soin ((s’)occuper (de) son corps et son esprit, estime de soi…). Ainsi, cultiver des produits alimentaires dans son faaapu est une forme de « Résistance par la subsistance » (Rainville 2025), il ne s’agit pas seulement de « faire sans » (avec des ressources limitées, un foncier réduit…), mais de « faire avec » (avec ce qu’on possède, ou ce qu’on peut mobiliser). Il s’agit d’une forme de « résistance ordinaire » ancrée dans la vie quotidienne (Dobré 2002), qui peut, dans une certaine mesure, être assimilée à une forme de mobilisation écologique (Pruvost 2025)
Nouvelle-Calédonie : une première analyse géopolitique de l’Accord de Bougival
No full textInternational audienceWith New Caledonia's institutional future still uncertain and Manuel Valls embarking on four days of decisive talks with the Kanak Socialist National Liberation Front in Nouméa, we publish an initial geopolitical analysis of the agreement signed on July 12 in Bougival. Between imperial rivalries and local dynamics, a multi-scale analysis.Alors que l’avenir institutionnel de la Nouvelle-Calédonie est toujours incertain et que Manuel Valls entame quatre jours d'échanges décisifs avec le Front de libération nationale kanak et socialiste à Nouméa, nous publions une première analyse géopolitique de l'accord signé le 12 juillet à Bougival. Entre rivalités impériales et dynamiques locales, une analyse multiscalaire
Leptospirosis: a critical zone disease?
No full textInternational audienceLeptospirosis is a zoonosis caused by pathogenic Leptospira present in the kidneys of asymptomatic (invasive) mammals , and shed in the environment with their urine. Pathogenic Leptospira (pL) are able to survive for extended periods in soil and are remobilized during rain events if they are located near the soil surface. Rainfall is recognized as a major driver of Leptospirosis infections in the Pacific. We report results from pL, sampling, modeling and interpretation in two contrasting rivers in New Caledonia, which is a hot-spot for leptospirosis in the tropical Pacific. The first river (Tho) drains a 3 km² catchment on the wet (2700 mm yearly rainfall) and windward coast, while the second one (Foa) drains a 120 km² catchment on the dryer (1800 mm) west coast. Both areas are strongly affected by leptospirosis. Three rain events and one low water period were sampled in each catchment, resulting in pL concentrations exceeding 1e5 pL/l for Tho and 1e4 pL/l for Foa. Only weak correlations (max=0.4) were found between river pL concentration and any hydrological variable (rainfall, water level (in Tho and Foa) or turbidity and soil moisture (in Tho)), although the increase in pL concentration was obviously associated with heavy rainfall and water level rise. However a non-linear model based on a 4-layer neural network working with the water level was able to explain 73% of the variance of the decimal log of whole dataset. Similar results were obtained with a model based on rainfall (71 % explained variance). Although there was a strong contrast in catchment size and or climate between Foa and Tho, both models worked fairly well for both catchments. However, neither a model fitted only to Tho or only to Foa could fairly reproduce data for both catchments. PL data were consistent with Leptospira being able to move upward with the rising capillary fringe in soils of the catchment (during wet periods) or of the river banks (during minor water level rises associated to dryer period). Leptospirosis is an environmental disease involving the critical zone as well as animal and human behavior. A One Health approach is recommended to address this disease