Climate variability and trends in downscaled high-resolution simulations and projections over Metropolitan France

In order to fulfill the society demand for climate information at the spatial scale allowing impact studies, long-term high-resolution climate simulations are produced, over an area covering metropolitan France. One of the major goals of this article is to investigate whether such simulations appropriately simulate the spatial and temporal variability of the current climate, using two simulation chains. These start from the global IPSL-CM4 climate model, using two regional models (LMDz and MM5) at moderate resolution (15–20 km), followed with a statistical downscaling method in order to reach a target resolution of 8 km. The statistical downscaling technique includes a non-parametric method that corrects the distribution by using high-resolution analyses over France. First the uncorrected simulations are evaluated against a set of high-resolution analyses, with a focus on temperature and precipitation. Uncorrected downscaled temperatures suffer from a cold bias that is present in the global model as well. Precipitations biases have a season- and model-dependent behavior. Dynamical models overestimate rainfall but with different patterns and amplitude, but both have underestimations in the South-Eastern area (Cevennes mountains) in winter. A variance decomposition shows that uncorrected simulations fairly well capture observed variances from inter-annual to high-frequency intra-seasonal time scales. After correction, distributions match with analyses by construction, but it is shown that spatial coherence, persistence properties of warm, cold and dry episodes also match to a certain extent. Another aim of the article is to describe the changes for future climate obtained using these simulations under Scenario A1B. Results are presented on the changes between current and mid-term future (2021–2050) averages and variability over France. Interestingly, even though the same global climate model is used at the boundaries, regional climate change responses from the two models significantly differ.     

Magnitude of latent heat in thermally loaded clays

Temperature changes are known to induce specific couplings in clay, in particular, an anomalously high thermal pressurization in undrained conditions or a thermal compaction in drained conditions, both of which are potential threats for the mechanical stability and sealing capacity of the geomaterials. Thermodynamical analysis of those peculiar thermomechanical couplings points to a potentially important latent energy, which in turn could limit the temperature change upon heating or cooling. The direct measurement of latent energy developed during a laboratory geomechanical test is challenging. Instead, proper identification of thermal hardening in conventional experiments with temperature changes provides an alternative route to estimate latent energy. In this work, existing laboratory thermomechanical tests of clays are analyzed with a rigorous thermodynamic framework to quantify the magnitude of latent energy in thermomechanically loaded clays. A thermodynamically consistent constitutive model for fully saturated clays that combines two key features, (a) the temperature dependence of the blocked energy and (b) the framework of bounding plasticity, is proposed. The performance of the model is validated by reproducing results obtained in laboratory tests for Boom and Opalinus clays. The thermomechanical loads considered to validate the model performance were then used to estimate the percentage of work that remains latent in the clayey material during plastic yielding. We find that the magnitude of latent energy is quite significant, typically a few tens of percent of the total dissipated energy, and increases significantly with temperature. Accordingly, it is expected to play an important role in the thermomechanical response of clays.     

Assessment of gully erosion rates through interviews and measurements: a case study from northern Ethiopia

Gullying has been widespread in the Ethiopian Highlands during the 20th century. It threatens the soil resource, lowers crop yields in intergully areas through enhanced drainage and desiccation, and aggravates flooding and reservoir siltation. Knowing the age and rates of gully development during the last few decades will help explain the reasons for current land degradation. In the absence of historical written or photographic documentation, the AGERTIM method (Assessment of Gully Erosion Rates Through Interviews and Measurements) has been developed. It comprises measurements of contemporary gully volumes, monitoring of gully evolution over several years and semi‐structured interview techniques. Gully erosion rates in the Dogu'a Tembien District, Tigray, Ethiopia, were estimated in three representative case‐study areas. In Dingilet, gullying started around 1965 after gradual environmental changes (removal of vegetation from cropland in the catchment and eucalyptus plantation in the valley bottom); rill‐like incisions grew into a gully, which increased rapidly in the drier period between 1977 and 1990. The estimated evolution of the total gully volume in the other areas show patterns similar to those of the Dingilet gully. Average gully erosion rate over the last 50 years is 6·2 t ha^?1 a^?1. Since 1995, no new gullies have developed in the study area. Area‐specific short‐term gully erosion rates are now on average 1·1 t ha^?1 a^?1. The successful application of the AGERTIM method requires an understanding of the geomorphology of the study area and an integration of the researchers with the rural society. It reveals that rapid gully development in the study area is some 50 years old and is mainly caused by human‐induced environmental degradation. Under the present‐day conditions of ‘normal’ rain and catchment‐wide soil and water conservation, gully erosion rates are decreasing. Copyright © 2006 John Wiley & Sons, Ltd.     

The information system of the French Peatland Observation Service: Service National d'Observation Tourbières – A valuable tool to assess the impact of global changes on the hydrology and biogeochemistry of temperate peatlands through long term monitoring

Mitigating and adapting to global changes requires a better understanding of the response of the Biosphere to these environmental variations. Human disturbances and their effects act in the long term (decades to centuries) and consequently, a similar time frame is needed to fully understand the hydrological and biogeochemical functioning of a natural system. To this end, the ‘Centre National de la Recherche Scientifique’ (CNRS) promotes and certifies long-term monitoring tools called national observation services or ‘Service National d'Observation’ (SNO) in a large range of hydrological and biogeochemical systems (e.g., cryosphere, catchments, aquifers). The SNO investigating peatlands, the SNO ‘Tourbières’, was certified in 2011 ( https://www.sno-tourbieres.cnrs.fr/ ). Peatlands are mostly found in the high latitudes of the northern hemisphere and French peatlands are located in the southern part of this area. Thus, they are located in environmental conditions that will occur in northern peatlands in coming decades or centuries and can be considered as sentinels. The SNO Tourbières is composed of four peatlands: La Guette (lowland central France), Landemarais (lowland oceanic western France), Frasne (upland continental eastern France) and Bernadouze (upland southern France). Thirty target variables are monitored to study the hydrological and biogeochemical functioning of the sites. They are grouped into four datasets: hydrology, fluvial export of organic matter, greenhouse gas fluxes and meteorology/soil physics. The data from all sites follow a common processing chain from the sensors to the public repository. The raw data are stored on an FTP server. After operator or automatic processing, data are stored in a database, from which a web application extracts the data to make them available ( https://data-snot.cnrs.fr/data-access/ ). Each year at least, an archive of each dataset is stored in Zenodo, with a digital object identifier (DOI) attribution ( https://zenodo.org/communities/sno_tourbieres_data/ ).     

Evolution paragénétique de la minéralisation uranifère de Chaméane (Puy-de-Dôme), France: chaméanite,geffroyite et giraudite,trois séléniures nouveaux de Cu,Fe, Ag et As

Résumé Trois séléniures nouveaux ont été découverts dans la minéralisation unranifère à séléniures et sulfures de Chaméane, France. Geffroyite, (Cu, Fe, Ag)₉(Se, S)₈, cubique,Fm3m,a=10.889 ,Z=4; structure type pentlandite. Densité calculée 5.39 g/cm³. Les raies les plus intenses du diagramme de poudre sont: 9 3.282 (311); 9 3.145 (222); 6 2.094 (511;333); 10 1.925 (440); 5 1.660 (533); 6 1.112 (844). Microdureté Vickers 70 kg/mm². Brun crème en lumière réfléchie, réflectances: 19.0 (420), 27.5 (500), 30.1 (540), 33.6 (600), 35.8 (660), 36.9 (700 nm). Chaméanite. Les analyses à la microsonde correspondent à (Cu_3.46Fe_0.52)_3.98 (As_0.94 Sb_0.02)_0.96(Se_3.72S_0.34)_4.06, formule idéale (Cu, Fe)₄As(Se, S)₄. Le rapport Cu/Fe varie de 6 à 13. Cubique,I---,a=11.039 ,Z=8, densité calculée 6.17 g/cm³. Raies les plus intenses du diagramme de poudre: 10 3.187 (222); 9 1.951 (440); 8 1.665 (622); 4 1.381 (800); 6 1.266 (662); 7 1.127 (844); 5 1.062 (10.2.2; 666). Microdureté Vickers 265 kg/mm². Gris foncé en section polie, plages à zonage complexe dû à des variations de Cu/Fe. Réflectances maximales: 27.1 (420), 26.6 (500), 27.1 (540), 27.7 (600), 28.2 (660); 28.7 (700 nm). Giraudite, (Cu, Zn, Ag)₁₂(As, Sb)₄(Se, S)₁₃. Cubique ,a=10.578 ,Z=2; structure type tétraédrite. Analogue arsénié de la hakite. Densité calculée 5.75 g/cm³. Raies les plus intenses du diagramme de poudre: 10 3.050 (222); 5 2.497 (411; 330); 6 1.932 (521); 9 1.868 (440); 7 1.593 (622). Microdureté Vickers 293 kg/mm². Gris clair, réflectances: 32.2 (420), 31.6 (500), 31.7 (540), 31.7 (600), 31.5 (660), 30.8 (700 nm).Trois épisodes minéralisants, séparés par des mouvements tectoniques, forment la paragenèse de Chaméane, comportant: barytine, pechblende, hématite, löllingite, mispickel, pyrite, chalcopyrite, clausthalite, tétraédrite, tennantite, bukovite, athabascaïte, umangite, berzelianite, klockmannite, eucaïrite, geffroyite, chaméanite, giraudite, eskebornite.

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Paragenetic evolution of the uranium mineralization rich in selenides at chaméane (Puy-de Dôme), France: Chaméanite, geffroyite and giraudite, three new selenides of Cu, Fe, Ag and As

Summary Three new selenides occur in the uranium mineralization rich in selenides and sulphides at Chaméane, France. Geffroyite, (Cu, Fe, Ag)₉(Se, S)₈, cubic,Fm3m,a=10.889 ,Z=4; pentlandite-like structure. Calculated density 5.39 g/cm³. The strongest lines in the X-ray powder pattern are: 9 3.282 (311); 9 3.145 (222); 6 2.094 (511; 333); 10 1.925 (440); 5 1.660 (533); 6 1.112 (844). Vickers microhardness 70 kg/mm². In reflected light, it has a brown colour with a cream tint. Reflectances: 19.0 (420), 27.5 (500), 30.1 (540), 33.6 (600), 35.8 (660), 36.9 (700 nm). Chaméanite. Microprobe analyses gave (Cu_3.46Fe_0.52)_3.98(As_0.94Sb_0.02)_0.96(Se_3.72S_0.34)_4.06; ideal formula is (Cu, Fe)₄As(Se, S)₄. The Cu/Fe ratio varies from 6 to 13. CubicI---,a=11.039 ,Z=8, calculated density 6.17 g/cm³. Strongest lines in the powder pattern: 10 3.187 (222); 9 1.951 (440); 8 1.665 (622); 4 1.381 (800); 6 1.266 (622); 7 1.127 (844); 5 1.062 (10.2.2; 666). Vickers microhardness 265 kg/mm². Dark grey in reflected light. Some grains exhibit irregular zoning due to variations of Cu/Fe ratio. Maximum reflectances: 27.1 (420), 26.6 (500), 27.1 (540); 27.7 (600), 28.2 (660), 28.7 (700 nm). Giraudite, (Cu, Zn, Ag)₁₂(As, Sb)₄(Se, S)₁₃. Cubic, ,a=10.578 ,Z=2; member of tetrahedrite series. Arsenian analogue of hakite. Calculated density 5.75 g/cm³. Strongest lines in the powder pattern: 10 3.050 (222); 5 2.497 (411; 330); 6 1.932 (521); 9 1.868 (440); 7 1.593 (622). Vickers microhardness 293 kg/mm². Light grey in reflected light, reflectances: 32.2 (420), 31.6 (500), 31.7 (540), 31.7 (600), 31.5 (660), 30.8 (700 nm). The mineralization of the Chaméane deposit consists of three cycles separated by tectonic movements. The minerals found are: barite, pitchblende, hematite, löllingite, arsenopyrite, pyrite, chalcopyrite, clausthalite, tetrahedrite, tennanite, bukovite, athabascaite, umangite, berzelianite, klockmannite, eucairite, geffroyite, chaméanite, giraudite and eskebornite.

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Avec 5 Figures     

Simulation des changements climatiques au cours du XXIe siècle incluant l'ozone stratosphériqueSimulation of climate changes during the 21st century including stratospheric ozone

Two climate simulations of 150 years, performed with a coupled ocean/sea-ice/atmosphere model including stratospheric ozone, respectively with and without heterogeneous chemistry, simulate the tropospheric warming associated with an increase of the greenhouse effect of carbon dioxide and other trace gases since 1950 and their impact on sea–ice extent, as well as the stratospheric cooling and its impact on ozone concentration. The scenario with heterogeneous chemistry reproduces the formation of the ozone hole over the South Pole from the 1970s and its deepening until the present time, and shows that the ozone hole should progressively fill during the coming decades. To cite this article: J.-F. Royer et al., C. R. Geoscience 334 (2002) 147–154.     

Assessment of annual high‐water events for the Mackenzie River basin,Canada

River ice break‐up is known to have important morphological, ecological and socio‐economic effects on cold‐regions river environments. One of the most persistent effects of the spring break‐up period is the occurrence of high‐water events. A return‐period assessment of maximum annual nominal water depths occurring during the spring break‐up and open‐water season at 28 Water Survey of Canada hydrometric sites over the 1913–2002 time period in the Mackenzie River basin is presented. For the return periods assessed, 13 (14) stations are dominated by peak events occurring during the spring break‐up (open‐water) season. One location is determined to have a mixed signal. A regime classification is proposed to separate ice‐ and open‐water dominated systems. As part of the regime classification procedure, specific characteristics of return‐period patterns including alignment, and difference between the 2 and 10‐year events are used to identify regime types. A dimensionless stage‐discharge plot allows for a contrast of the relative magnitudes of flows required to generate maximum nominal water‐depth events in the different regimes. At sites where discharge during the spring break‐up is approximately one‐quarter or greater than the magnitude of the peak annual discharge, nominal water depths can be expected to exceed those occurring during the peak annual discharge event. Several physical factors (location, basin area, stream order, gradient, river orientation, and climate) are considered to explain the differing regimes and discussed relative to the major sub‐regions of the MRB. Copyright © 2008 John Wiley & Sons, Ltd and Her Majesty the Queen in right of Canada.