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.     

Environmental conservation and the production of new territories: the example of French départements

Very important initiatives have been taken and policies have been adopted in the European Union to protect areas of great importance for threatened species and habitats. Protected areas differ broadly in terms of category, natural conditions and administrative organisation, from international initiative such as Biosphere Reserves, European ones with Natura 2000 network until the institution of national and regional protected areas. In France, the administrative subdivisions known as “départements” were created with the French Revolution in the end of the eighteenth century; in 1985 an original and autonomous procedure to establish special protected areas, called “Sensitive Natural Spaces” (SNS) was devolved to them. The scope of this paper is to present an overview of these devolved powers which enable French départements to create protected areas and to levy a departmental tax on sensitive natural spaces (DTSNS). We statistically studied some parameters by multivariate methods in order to explain the choices of this policy by the départements. The huge variations in the way these powers are implemented prove the development of new environmental territories.     

Schooling behaviour and environmental forcing in relation to anchoveta distribution: An analysis across multiple spatial scales

The Peruvian anchovy or anchoveta (Engraulis ringens) supports the highest worldwide fishery landings and varies in space and time over many scales. Here we present the first comprehensive sub-mesocale study of anchoveta distribution in relation to the environment. During November 2004, we conducted a behavioural ecology survey off central Peru and used a series of observational and sampling tools including SST and CO₂ sensors, Niskin bottles, CTD probes, zooplankton sampling, stomach content analysis, echo-sounder, multibeam sonar, and bird observations. The sub-mesoscale survey areas were chosen from mesoscale acoustic surveys. A routine coast-wide (2000 km) acoustic survey performed just after the sub-mesoscale surveys, provided information at an even larger population scale. The availability of nearly concurrent sub-mesoscale, mesoscale and coast-wide information on anchoveta distribution allowed for a unique multi-scale synthesis. At the sub-mesoscale (100s m to km) physical processes (internal waves and frontogenesis) concentrated plankton into patches and determined anchoveta spatial distribution. At the mesoscale (10s km) location relative to the zone of active upwelling (and age of the upwelled water) and the depth of the oxycline had strong impacts on the anchoveta. Finally, over 100s km the size of the productive area, as defined by the upwelled cold coastal waters, was the determining factor. We propose a conceptual view of the relative importance of social behaviour and environmental (biotic and abiotic) processes on the spatial distribution of anchoveta. Our ecological space has two y-axis; one based on self-organization (social behaviour), and the other based on the environmental processes. At scales from the individual (10s cm), to the nucleus (m), social behaviour (e.g. the need to school) drives spatial organization. At scales larger than the school, environmental forces are the main driver of fish distribution. The conceptual ecosystem models presented in this paper may provide the final links needed to develop accurate forecasts of the spatial distribution of anchoveta over multiple scales.     

TESSIN VISLab—laboratory for scientific visualization

Scientific visualization is an integral part of the modeling workflow, enabling researchers to understand complex or large data sets and simulation results. A high-resolution stereoscopic virtual reality (VR) environment further enhances the possibilities of visualization. Such an environment also allows collaboration in work groups including people of different backgrounds and to present results of research projects to stakeholders or the public. The requirements for the computing equipment driving the VR environment demand specialized software applications which can be run in a parallel fashion on a set of interconnected machines. Another challenge is to devise a useful data workflow from source data sets onto the display system. Therefore, we develop software applications like the OpenGeoSys Data Explorer, custom data conversion tools for established visualization packages such as ParaView and Visualization Toolkit as well as presentation and interaction techniques for 3D applications like Unity. We demonstrate our workflow by presenting visualization results for case studies from a broad range of applications. An outlook on how visualization techniques can be deeply integrated into the simulation process is given and future technical improvements such as a simplified hardware setup are outlined.     

Residential mobility trajectories and integration in Douala and Bafoussam,Cameroon

Abstract

This study examines how migrant households relocate their homes in two Cameroonian cities over the course of lifetimes or even generations. The central claim is that homeownership is the ultimate sign of integration into city life. Using qualitative and quantitative research methods (218 interviews, 30 focus groups and a household survey, sample size 686), the study argues that three key factors explain why people move: the quality of housing they can affords, the proximity to a workplace and the potential for homeownership. Three residential model trajectories are identified. The first describes a journey from being a new migrant who is a guest of family or friends in the city centre to being a married family with kids owning a home in the urban periphery. The second model continues that journey by returning back to the city centre in pursuit of more convenient, high-status home location (if finances permit). A third model describes moves to sites all over the city later in life as older individuals seek to maximize family income in the way they use multiple properties. Understanding residential mobility patterns has the potential to lead to a better public policies and more effective private investments in the housing sector.     

Precipitation and temperature space–time variability and extremes in the Mediterranean region: evaluation of dynamical and statistical downscaling methods

This study evaluates how statistical and dynamical downscaling models as well as combined approach perform in retrieving the space–time variability of near-surface temperature and rainfall, as well as their extremes, over the whole Mediterranean region. The dynamical downscaling model used in this study is the Weather Research and Forecasting (WRF) model with varying land-surface models and resolutions (20 and 50 km) and the statistical tool is the Cumulative Distribution Function-transform (CDF-t). To achieve a spatially resolved downscaling over the Mediterranean basin, the European Climate Assessment and Dataset (ECA&D) gridded dataset is used for calibration and evaluation of the downscaling models. In the frame of HyMeX and MED-CORDEX international programs, the downscaling is performed on ERA-I reanalysis over the 1989–2008 period. The results show that despite local calibration, CDF-t produces more accurate spatial variability of near-surface temperature and rainfall with respect to ECA&D than WRF which solves the three-dimensional equation of conservation. This first suggests that at 20–50 km resolutions, these three-dimensional processes only weakly contribute to the local value of temperature and precipitation with respect to local one-dimensional processes. Calibration of CDF-t at each individual grid point is thus sufficient to reproduce accurately the spatial pattern. A second explanation is the use of gridded data such as ECA&D which smoothes in part the horizontal variability after data interpolation and damps the added value of dynamical downscaling. This explains partly the absence of added-value of the 2-stage downscaling approach which combines statistical and dynamical downscaling models. The temporal variability of statistically downscaled temperature and rainfall is finally strongly driven by the temporal variability of its forcing (here ERA-Interim or WRF simulations). CDF-t is thus efficient as a bias correction tool but does not show any added-value regarding the time variability of the downscaled field. Finally, the quality of the reference observation dataset is a key issue. Comparison of CDF-t calibrated with ECA&D dataset and WRF simulations to local measurements from weather stations not assimilated in ECA&D, shows that the temporal variability of the downscaled data with respect to the local observations is closer to the local measurements than to ECA&D data. This highlights the strong added-value of dynamical downscaling which improves the temporal variability of the atmospheric dynamics with regard to the driving model. This article highlights the benefits and inconveniences emerging from the use of both downscaling techniques for climate research. Our goal is to contribute to the discussion on the use of downscaling tools to assess the impact of climate change on regional scales.     

Impacts of forest conversion and agriculture practices on water pathways in Southern Brazil

Land‐use/cover change (LUCC), and more specifically deforestation and multidecadal agriculture, is one of the various controlling factors of water fluxes at the hillslope or catchment scale. We investigated the impact of LUCC on water pathways and stream stormflow generation processes in a subtropical region in southern Brazil. We monitored, sampled and analysed stream water, pore water, subsurface water, and rainwater for dissolved silicon concentration (DSi) and ¹⁸O/¹⁶O (δ¹⁸O) signature to identify contributing sources to the streamflow under forest and under agriculture. Both forested and agricultural catchments were highly responsive to rainfall events in terms of discharge and shallow groundwater level. DSi versus δ¹⁸O scatter plots indicated that for both land‐use types, two run‐off components contributed to the stream discharge. The presence of a dense macropore network, combined with the presence of a compact and impeding B‐horizon, led to rapid subsurface flow in the forested catchment. In the agricultural catchment, the rapid response to rainfall was mostly due to surface run‐off. A 2‐component isotopic hydrograph separation indicated a larger contribution of rainfall water to run‐off during rainfall event in the agricultural catchments. We attributed this higher contribution to a decrease in topsoil hydraulic conductivity associated with agricultural practices. The chemical signature of the old water component in the forested catchment was very similar to that of the shallow groundwater and the pore soil water: It is therefore likely that the shallow groundwater was the main source of old water. This is not the case in the agricultural catchments where the old water component had a much higher DSi concentration than the shallow groundwater and the soil pore water. As the agricultural catchments were larger, this may to some extent simply be a scale effect. However, the higher water yields under agriculture and the high DSi concentration observed in the old water under agriculture suggest a significant contribution of deep groundwater to catchment run‐off under agriculture, suggesting that LUCC may have significant effects on weathering rates and patterns.     

Tropical peatlands: current plight and the need for responsible management

Peatlands are important carbon stores, but when drained (e.g. for agriculture), this carbon is released to the atmosphere as carbon dioxide (CO₂, a greenhouse gas). Globally, at least 15% of peatlands have been drained, mostly in Europe and South‐east Asia, and are responsible for 5% of human‐derived CO₂ emissions. Peatlands have been exploited for generations, but not without local to global consequences, particularly in South‐East Asia. However, recognition of the continuous environmental toll caused by peatland exploitation is leading to a need to change attitudes and practices, in order to propel a move towards a more balanced and responsible use of peat in both northern and tropical peatlands.     

Fast switch from extensional exhumation to thrusting of the Ronda Peridotites (South Spain)

The Alboran Domain, situated at the western end of the Mediterranean subduction system, is characterized by the Ronda Peridotites, one of the world's largest exposures of sub‐continental mantle. Using U–Pb (LA‐ICP‐MS) and Ar–Ar dating, we precisely dated two tectonic events associated with the Tertiary exhumation of the Ronda Peridotites. First, shearing along the Crust–Mantle Extensional Shear Zone caused, at ca. 22.5 Ma, mantle exhumation, local partial melting in the deep crust and coeval cooling in the upper crust. Second, the Ronda Peridotites Thrust triggered the final emplacement of the peridotites onto the continental crust at c. 21 Ma, as testified by granitic intrusions in the thrust hangingwall. The tectonic evolution of the western Alboran Domain is therefore characterized by a fast switch from continental lithospheric extension in a backarc setting, with sub‐continental mantle exhumation, to a rift inversion by thrusting driven by shortening of the upper plate.