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Ayadi K.,University of Science and Technology Houari Boumediene | Boutiba M.,University of Science and Technology Houari Boumediene | Sabatier F.,CNRS European Center for Research and Education in Environmental Geosciences | Sabatier F.,Aix - Marseille University | Guettouche M.S.,University of Science and Technology Houari Boumediene
Arabian Journal of Geosciences | Year: 2016

The Bejaia coastline is one of the most beautiful and attractive coastlines in Algeria; this is due to its landscape and ecological diversity running along it. The eastern coast of Bejaia is formed by a wide stretch of sand, occupying the bottom of the bay. Its beaches are fed by sediments carried by two main wadis that debouch into the bay: Soummam in the west and Agrioun in the east. The undertaken work in this article focuses on the study of coastal erosion, which has a significant damage on the natural patrimony. This erosion risk in perpetual evolution, by location, is dramatically affecting the beautiful sandy beaches and various infrastructures over all the coast length of the Bejaia bay. In order to map and evaluate this risk, a methodological approach has been followed. This approach is mainly based on a diachronic variation analysis in the position of the shoreline over a period of 60 years; based on a series of ortho-rectified aerial photos, satellite images, as well as DGPS topographic surveys on the ground. The results revealed significant variations in the position of the shoreline during the last 60 years, especially on both sides of Soummam and Agrioun wadis. The most observed retreat of the shoreline is in the western part of the coast, where the rate of evolution reached −7.89 m/year (beach of Sidi Ali Lebhar), whereas the shoreline retreat reached −1.75 m/year in the center of the bay and −2 m/year toward the east. © 2015, Saudi Society for Geosciences.

Gaucherel C.,French National Institute for Agricultural Research | Moron V.,CNRS European Center for Research and Education in Environmental Geosciences
International Journal of Climatology | Year: 2016

'Tipping points' (TPs) are thresholds of potentially disproportionate changes in the Earth's climate system associated with future global warming and are considered today as a 'hot' topic in environmental sciences. In this study, TP interactions are analysed from an integrated and conceptual point of view using two qualitative Boolean models built on graph grammars. They allow an accurate study of the node TP interactions previously identified by expert elicitation and take into account a range of various large-scale climate processes potentially able to trigger, alone or jointly, instability in the global climate. Our findings show that, contrary to commonly held beliefs, far from causing runaway changes in the Earth's climate, such as self-acceleration due to additive positive feedbacks, successive perturbations might actually lead to its stabilization. A more comprehensive model defined TPs as interactions between nine (non-exhaustive) large-scale subsystems of the Earth's climate, highlighting the enhanced sensitivity to the triggering of the disintegration of the west Antarctic ice sheet. We are claiming that today, it is extremely difficult to guess the fate of the global climate system as TP sensitivity depends strongly on the definition of the model. Finally, we demonstrate the stronger effect of decreasing rules (i.e. mitigating connected TPs) over other rule types, thus suggesting the critical role of possible 'stabilizing points' that are yet to be identified and studied. © 2016 Royal Meteorological Society.

Moron V.,Aix - Marseille University | Moron V.,Columbia University | Barbero R.,Aix - Marseille University | Borgniet L.,IRSTEA | And 2 more authors.
Journal of Applied Meteorology and Climatology | Year: 2013

An empirical statistical scheme for predicting September-December fires in New Caledonia in the southwestern Pacific Ocean region using a cross-validated generalized linear model has been developed for the 2000-10 period. The predictor employs July sea surface temperatures (SST) recorded over the Niño-4 box (58S-58N, 1608-2108E), which are closely related to austral spring (September-November) rainfall anomalies across New Caledonia. The correlation between the logarithm of observed and simulated total burned areas across New Caledonia is 0.87. A decrease in the local-scale skill (median correlation between the log of observed and simulated total burned areas in a 20-km radius around a rain gauge 5 0.46) around the main town (Nouméa) and its suburbs in the southwest of Grande Terre, and also in northern New Caledonia, could be associated either with a weaker climatic forcing from the Niño-4 SST index or a small-scale climatic forcing not linearly related to the El Niño-Southern Oscillation (ENSO) phenomenon. It is more likely that the decrease is tied to the influence of human-driven factors that blur the regional-scale climatic signal mostly associated with central Pacific ENSO events. © 2013 American Meteorological Society.

Goncalves J.,Aix - Marseille University | Vallet-Coulomb C.,Aix - Marseille University | Petersen J.,Aix - Marseille University | Hamelin B.,Aix - Marseille University | Deschamps P.,CNRS European Center for Research and Education in Environmental Geosciences
Journal of Hydrology | Year: 2015

The stable isotopes of water were used to improve the determination of the groundwater budget of the deep Saharan "Continental Intercalaire" (CI), a deep confined aquifer. Mixing processes between the CI and shallower aquifers have been described in several regional studies over the last few decades, based on observed isotopic differences between local water masses. Here, we improve the quantitative determination of the discharge flux of this aquifer in one of its main outlet regions, the Djeffara plain in Tunisia, based on geostatistics and a simple mass balance mixing model, applied before and after the beginning of extensive pumping in the 1970s. First, the average values of δ18O and δ2H were precisely documented in the mixing zone between CI water and the local recharge, based on conditional simulations using spatially distributed isotopic data. Together with the available estimate of local recharge and conservative hypotheses on the isotopic end-members, we estimate the discharge flux of the CI in the Djeffara plain at 1.78±1.03m3s-1 in 1970, probably near natural steady-state, reduced to 1.02±0.58m3s-1 in 2004 under strong anthropogenic pressure, related to the drastic increase in pumping rates in the deep CI aquifer during this period. Considering the general groundwater budget over the entire CI aquifer, we estimate a recharge value of 5.13m3s-1, or 6.5mmyr-1 over the 25,000km2 of recharge area in the Saharan Atlas. This value is in line with the evaluation of 2.1mmyr-1 obtained recently from the GRACE satellite gravity data for the overall outcrops considering that recharge occurs mostly in the Atlas region. © 2015 Elsevier B.V.

Ibanez T.,CNRS European Center for Research and Education in Environmental Geosciences | Ibanez T.,Laboratoire Of Botanique Et Decologie Vegetale Appliquees | Curt T.,IRSTEA | Hely C.,CNRS European Center for Research and Education in Environmental Geosciences
Journal of Vegetation Science | Year: 2013

Questions: How do early secondary successional forest species that grow in savannas differ in their tolerance to surface fires? What are the consequences of these fire tolerances for savanna-forest dynamics and landscape management? Location: Anthropogenic savannas in the New Caledonian biodiversity hotspot (SW Pacific). Methods: We estimated the range of fire intensity in New Caledonian savannas using field survey of fuels and the BehavePlus fire behaviour model. Within the predicted range of fire line intensity, we assessed theoretical fire injury to the cambium and crown for 11 species: the dominant tree of New Caledonian savannas (Melaleuca quinquenervia) and early secondary successional forest species. Using empirical models, for each species we estimated cambium damage from depth of necrosis (as a function of fire line intensity and fire residence time) and bark thickness, and crown damage from scorch height (as a function of fire line intensity) and tree height. We compared bark thickness and tree height increment patterns among species as well as species potential fire tolerance. Results: The 11 species had very contrasting capacity to avoid fire injury to the bole cambium due to differences in bark investment patterns, but were all very exposed to scorching and crown injury. Overall, most of sampled individuals are likely top-killed by low intensity fires (<1000 kW·m-1), which are frequent according to our simulations. Conclusions: The early secondary successional forest species growing in New Caledonian savannas are poorly adapted to fire, in comparison with literature on worldwide trees in savannas. As a result, their juveniles are unlikely to reach adult size in fire-prone areas. Restoration using the most fire-tolerant species and fire prevention may be complementary strategies to manage such tropical landscapes in order to conserve biodiversity and ecosystem services. We used a combination of allometric relationships and models of fire behaviour with fire injuries to assess how savanna and early secondary successional forest species differ in their tolerance to fires. We showed that the tolerance of these species to fire is highly variable and that the investment in bark thickness seems to be the prevailing trait that differentiates them. © 2012 International Association for Vegetation Science.

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