A statistical algorithm for estimating chlorophyll concentration in the New Caledonian lagoon

Spatial and temporal dynamics of phytoplankton biomass and water turbidity can provide crucial information about the function, health and vulnerability of lagoon ecosystems (coral reefs, sea grasses, etc.). A statistical algorithm is proposed to estimate chlorophyll-a concentration ([chl-a]) in optically complex waters of the New Caledonian lagoon from MODIS-derived remote-sensing reflectance (R-rs). The algorithm is developed via supervised learning on match-ups gathered from 2002 to 2010. The best performance is obtained by combining two models, selected according to the ratio of R-rs in spectral bands centered on 488 and 555 nm: a log-linear model for low [chl-a] (AFLC) and a support vector machine (SVM) model or a classic model (OC3) for high [chl-a]. The log-linear model is developed based on SVM regression analysis. This approach outperforms the classical OC3 approach, especially in shallow waters, with a root mean squared error 30% lower. The proposed algorithm enables more accurate assessments of [chl-a] and its variability in this typical oligo- to meso-trophic tropical lagoon, from shallow coastal waters and nearby reefs to deeper waters and in the open ocean

Wildfire risk for main vegetation units in a biodiversity hotspot : modeling approach in New Caledonia, South Pacific

Wildfire has been recognized as one of the most ubiquitous disturbance agents to impact on natural environments. In this study, our main objective was to propose a modeling approach to investigate the potential impact of wildfire on biodiversity. The method is illustrated with an application example in New Caledonia where conservation and sustainable biodiversity management represent an important challenge. Firstly, a biodiversity loss index, including the diversity and the vulnerability indexes, was calculated for every vegetation unit in New Caledonia and mapped according to its distribution over the New Caledonian mainland. Then, based on spatially explicit fire behavior simulations (using the FLAMMAP software) and fire ignition probabilities, two original fire risk assessment approaches were proposed: a one-off event model and a multi-event burn probability model. The spatial distribution of fire risk across New Caledonia was similar for both indices with very small localized spots having high risk. The patterns relating to highest risk are all located around the remaining sclerophyll forest fragments and are representing 0.012% of the mainland surface. A small part of maquis and areas adjacent to dense humid forest on ultramafic substrates should also be monitored. Vegetation interfaces between secondary and primary units displayed high risk and should represent priority zones for fire effects mitigation. Low fire ignition probability in anthropogenic-free areas decreases drastically the risk. A one-off event associated risk allowed localizing of the most likely ignition areas with potential for extensive damage. Emergency actions could aim limiting specific fire spread known to have high impact or consist of on targeting high risk areas to limit one-off fire ignitions. Spatially explicit information on burning probability is necessary for setting strategic fire and fuel management planning. Both risk indices provide clues to preserve New Caledonia hot spot of biodiversity facing wildfires

Le risque de feux de brousse sur la Grande Terre de Nouvelle-Calédonie : l’Homme responsable, mais pas coupable

Depuis des années en Nouvelle-Calédonie, les feux anthropiques croissent en nombre, fréquence et étendue, menaçant la conservation des écosystèmes et devenant un danger pour les populations. Les estimations montrent que les feux de forêt et de brousse dévastent en moyenne chaque année de 20 000 à 50 000 ha soit près de 3 % de la superficie totale de l’archipel. Au delà de la perte de biodiversité, il en résulte le cortège des risques d’impacts indirects des incendies : assèchement des cours d’eau en saison sèche, appauvrissement des sols, accélération du processus de désertification, aggravation du ruissellement, augmentation de l’érosion des sols, phénomènes d’hypersédimentation, étouffement des récifs coralliens, etc., autant de maux qui affectent directement les populations locales et leur milieu de vie dont une grande partie se nourrit des produits d’une agriculture vivrière traditionnelle et ou d’une pêche artisanale. Cependant malgré les enjeux liés à la gestion de ce risque majeur, l’une des constatations que nous pouvons faire, au-delà du manque de moyens humains et techniques de lutte, est une connaissance fragmentaire sur la répartition et les causes des incendies en Nouvelle-Calédonie. Cette communication, présentant quelques résultats du programme ANR INC (Incendies et biodiversité des écosystèmes en Nouvelle-Calédonie), aura comme objectifs d’analyser la distribution spatiale de l’occurrence des feux détectés par les satellites MODIS. Ces informations seront croisées au travers d’un SIG à des indicateurs spatialisés de type statuts fonciers (terrains coutumiers/privé) socio-économiques (taux de chômage, niveau scolaire, origine ethnique..) afin d’identifier des facteurs corrélés aux départs d'incendies. Dans un deuxième temps, l’étude de la perception de ce risque chez les populations Kanak nous permettra de mettre en évidence les causes principales des feux de brousse non maîtrisés.In New Caledonia, for many years, anthropogenic fires have been increasing in number, frequency and extent, posing a threat to the conservation of ecosystems and a danger to human populations. Estimates show that forest fires and bushfires devastate an average of 20,000 to 50,000 ha a year, which represents about 3% of the total surface area of the archipelago. Above and beyond biodiversity loss, fires can cause a range of indirect negative impacts (dried-up watercourses in the dry season, soil depletion, accelerated desertification, increased run-off and soil erosion, hypersedimentation phenomena, smothering of coral reefs etc.), which directly affect the environment and local populations, many of whom rely on subsistence farming and/or small-scale fishing. However, despite the challenges associated with managing this major risk, it is clear that, in addition to the shortage of human and technical fire-fighting resources, the knowledge about the distribution and causes of fires in New Caledonia is fragmentary. This paper describes some of the results of the research project (Fires and ecosystem biodiversity in New Caledonia) and aims to analyse the spatial distribution of fires detected by the MODIS satellites. This information will be cross-referenced in a GIS with spatial indicators highlighting both land tenure (customary/private land) and socio-economic status (unemployment rates, educational attainment, ethnicity etc.) in order to identify factors relating to outbreaks of fire. Second, studying the perception of risk among the Kanak populations will allow us to highlight the main causes of uncontrolled bushfires

Predicting dengue fever outbreaks in French Guiana using climate indicators

Background Dengue fever epidemic dynamics are driven by complex interactions between hosts, vectors and viruses. Associations between climate and dengue have been studied around the world, but the results have shown that the impact of the climate can vary widely from one study site to another. In French Guiana, climate-based models are not available to assist in developing an early warning system. This study aims to evaluate the potential of using oceanic and atmospheric conditions to help predict dengue fever outbreaks in French Guiana. Methodology/Principal Findings Lagged correlations and composite analyses were performed to identify the climatic conditions that characterized a typical epidemic year and to define the best indices for predicting dengue fever outbreaks during the period 1991-2013. A logistic regression was then performed to build a forecast model. We demonstrate that a model based on summer Equatorial Pacific Ocean sea surface temperatures and Azores High sea-level pressure had predictive value and was able to predict 80% of the outbreaks while incorrectly predicting only 15% of the non-epidemic years. Predictions for 2014-2015 were consistent with the observed non-epidemic conditions, and an outbreak in early 2016 was predicted. Conclusions/Significance These findings indicate that outbreak resurgence can be modeled using a simple combination of climate indicators. This might be useful for anticipating public health actions to mitigate the effects of major outbreaks, particularly in areas where resources are limited and medical infrastructures are generally insufficient

Pleural Mesothelioma in New Caledonia: Associations with Environmental Risk Factors

International audienceBackground: High incidences of malignant mesothelioma (MM) have been observed in New Caledonia. Previous work has shown an association between MM and soil containing serpentinite. Objectives: We studied the spatial and temporal variation of MM and its association with environmental factors. Methods: We investigated the 109 MM cases recorded in the Cancer Registry of New Caledonia between 1984 and 2008 and performed spatial, temporal, and space-time cluster analyses. We conducted an ecological analysis involving 100 tribes over a large area including those with the highest incidence rates. Associations with environmental factors were assessed using logistic and Poisson regression analyses. Results: The highest incidence was observed in the Houaïlou area with a world age-standardized rate of 128.7 per 100,000 person-years [95% confidence interval (CI), 70.41-137.84]. A significant spatial cluster grouped 18 tribes (31 observed cases vs. 8 expected cases; p = 0.001), but no significant temporal clusters were identified. The ecological analyses identified serpentinite on roads as the greatest environmental risk factor (odds ratio = 495.0; 95% CI, 46.2-4679.7; multivariate incidence rate ratio = 13.0; 95% CI, 10.2-16.6). The risk increased with serpentinite surface, proximity to serpentinite quarries and distance to the peridotite massif. The association with serpentines was stronger than with amphiboles. Living on a slope and close to dense vegetation appeared protective. The use of whitewash, previously suggested to be a risk factor, was not associated with MM incidence. Conclusions: Presence of serpentinite on roads is a major environmental risk factor for mesothelioma in New Caledonia

Climate-Based Models for Understanding and Forecasting Dengue Epidemics

Dengue fever is a major public health problem in the tropics and subtropics. Since no vaccine exists, understanding and predicting outbreaks remain of crucial interest. Climate influences the mosquito-vector biology and the viral transmission cycle. Its impact on dengue dynamics is of growing interest. We analyzed the epidemiology of dengue in Noumea (New Caledonia) from 1971 to 2010 and its relationships with local and remote climate conditions using an original approach combining a comparison of epidemic and non epidemic years, bivariate and multivariate analyses. We found that the occurrence of outbreaks in Noumea was strongly influenced by climate during the last forty years. Efficient models were developed to estimate the yearly risk of outbreak as a function of two meteorological variables that were contemporaneous (explicative model) or prior (predictive model) to the outbreak onset. Local threshold values of maximal temperature and relative humidity were identified. Our results provide new insights to understand the link between climate and dengue outbreaks, and have a substantial impact on dengue management in New Caledonia since the health authorities have integrated these models into their decision making process and vector control policies. This raises the possibility to provide similar early warning systems in other countries