21 research outputs found
Hydroelectric production in Akosombo, and the development of irrigated agriculture upstream, a fair balance to be found to reconcile regional energy and food security. - Challenges of the Volta Basin Water Charter
The Volta River is a West African river that flows from Burkina Faso to Ghana where it empties into the Atlantic Ocean. It basin extends over six countries: Benin, Burkina Faso, CĂŽte dâIvoire, Ghana, Mali and Togo. These states, members of the Volta Basin Authority, have committed themselves to drawing up a Water Charter. One of the challenges of this international agreement is to agree on a reasonable level of abstraction to reconcile food and energy security for the populations, while guaranteeing the minimum needs of the ecosystems. Supported by an appropriation of the needs-resources balance through the use of LegoÂź bricks, their reflection was supported by a hydro-economic analysis. This analysis consisted in comparing the added value associated with an agricultural abstraction - which leads to a definitive consumption of water upstream of the basin, for example in BagrĂ© in Burkina Faso - and the one associated with the same quantity of water if it had been allowed to flow and turbined in one of the hydroelectric facilities located further downstream, for example in the large Akosombo dam in Ghana. The results show that the agricultural valorisation of a continuous abstraction of one m3/s, i.e. 30 Mm3 per year, allows to irrigate 1,500 ha and generates an added value of 1,300 M FCFA per year, i.e. 44 FCFA/m3. This volume of 30 Mm3, taken upstream of the dam would induce a loss of hydroelectric production of 6 GWh/year, worth 297 M FCFA, i.e. 10 FCFA/m3. The economic value of each m3 withdrawn to develop irrigated agriculture upstream of the basin is thus higher than that of each m3 turbined in the Akosombo-Kpong complex. Within the limit of an acceptable reduction of hydropower production, the economic development of the basin as a whole would thus benefit from the development of irrigated agriculture
Cylindrical cyclic acoustic imaging with a Bayesian approach for reconstruction of cyclostationary sources
International audienceStandard acoustic imaging techniques, such as beamforming or near acoustical holography, are now widely used in engineering contexts. However, large arrays of microphones are sometimes required to have a good resolution. Besides new challenges arise, particularly in the field of non stationary sources, which need to be identified and solved. Cyclostationary sound sources, a specific kind of non stationary signals, are characterized by statistical properties evolving periodically in time. In practice, the first-order statistical properties contain some periodic components while the second orders may be random with a periodic flow of energy. The present work tackles the acoustic imaging of cyclostationary sources with a scanning microphone, i.e., without any array. Cylindrical surfaces, adapted to standard rotating machines, are considered. The reconstruction difficulty of acoustic sources from discrete measurements is addressed here thanks to the cyclostationary properties. A cyclic sound field is hence extracted from the discrete measurements. Finally, a Bayesian formulation, gathering both physical and probabilistic information on this inverse problem, is used to back propagate the sound over the radiating surface
Les Pyrénées orientales face aux changements globaux: comparaison des effets des changements climatique et anthropique sur les besoins en eau
Dans les Pyrénées Orientales, la tendance à la décroissance du débit d'étiage des riviÚres observée au cours des derniÚres décennies devrait se poursuivre à l'avenir, pouvant accentuer les stress hydriques sur les milieux aquatiques et la compétition entre usages et usagers pour l'accÚs aux ressources.
Le projet de recherche ANR-VULCAIN a comparĂ© les impacts des changements climatique et socio-Ă©conomique sur les hydrosystĂšmes du territoire des PyrĂ©nĂ©es Orientales. Un couplage de mĂ©thodes de prospective participative et de modĂ©lisation ont Ă©tĂ© utilisĂ©s pour quantifier l'Ă©volution des prĂ©lĂšvements en eau sous l'effet de ces changements. Des scĂ©narios socio-Ă©conomiques ont Ă©tĂ© construits avec les acteurs du territoire, lors de sĂ©ances thĂ©matiques de travail en groupe (urbanisme et amĂ©nagement du territoire d'une part et agriculture d'autre part), dont les rĂ©sultats ont Ă©tĂ© quantifiĂ©s Ă l'aide de modĂšles pour en estimer les effets des changements anthropiques sur les prĂ©lĂšvements domestiques et agricoles. En parallĂšle, des scĂ©narios climatiques ont Ă©tĂ© utilisĂ©s dans le mĂȘme modĂšle agricole afin d'estimer les possibles impacts des changements climatiques sur les besoins agricoles.
Dans les scĂ©narios envisagĂ©s, l'Ă©volution des besoins nets en irrigation sous l'effet des changements anthropiques a une amplitude plus grande que l'Ă©volution des prĂ©lĂšvements pour l'eau potable ou les Ă©volutions des besoins nets en irrigation sous l'effet du changement climatique qui sont du mĂȘme ordre de grandeur. Des marges de manĆuvre existent pour satisfaire l'augmentation de ces besoins, en rĂ©visant les modes de distribution actuels pour les rendre plus efficients, en optimisant l'utilisation des capacitĂ©s de stockage, ou en utilisant des ressources de substitution.
Cet article présente l'approche utilisée, ainsi que quelques-uns des principaux résultats
Composer avec lâinvisible, lâincertain et le flou des frontiĂšres : les gestionnaires interprĂštes des chercheurs pour planifier la gestion des aquifĂšres dans la plaine du Roussillon
International audienceTerritorial groundwater management is complicated by the invisibility, complexity and uncertainties of the hydrogeological and social processes involved. The article deals with water management expert's interpretation of research results on hydrogeological processes, water uses, associated uncertainties and spatialization to guide public policy. The multilayer aquifer of the Roussillon plain provides the empirical basis for this work. A chronological timeline highlights the convergences, divergences and time or space shifts between scientific production and planning documents since the 1960s, on three major subjects (interactions between surface water and aquifers, vulnerability to overexploitation and risks of seawater intrusions). These distortions are analysed in terms of cognitive biases, pragmatic choices and socio-political pressures
Explore 2070 : quelle utilisation dâun exercice prospectif sur les impacts des changements climatiques Ă lâĂ©chelle nationale pour dĂ©finir des stratĂ©gies dâadaptation ?
Les changements climatiques projetĂ©s Ă lâhorizon du milieu du XXIe siĂšcle pourraient avoir des impacts importants sur la disponibilitĂ© en eau en France. LâĂ©tude prospective Explore 2070, pilotĂ©e par le ministĂšre chargĂ© de lâĂ©cologie, a ainsi mis en Ă©vidence la nĂ©cessitĂ© de quantifier et dâanticiper ces changements, et de construire des stratĂ©gies dâadaptation pour limiter leurs consĂ©quences nĂ©gatives sur les hydrosystĂšmes et les activitĂ©s humaines. Cet article analyse dans quelle mesure ces travaux ont pu contribuer Ă la sensibilisation des acteurs de lâeau et Ă la rĂ©flexion sur lâadaptation au changement climatique en France
Incertitudes climatiques et hydrologiques sur les projections de crues et d'Ă©tiages en France
[Departement_IRSTEA]Eaux [TR1_IRSTEA]ARCEAUInternational audienceChanges in river flows are associated with different types of uncertainties, due to an imperfect knowledge of both future climate and rainfall-runoff processes. Due to computational constraints, impact and adaptation studies unfortunately cannot always afford to perform a detailed analysis of all these uncertainties. In that case, the modelling efforts have to focus on the most relevant source of uncertainty in order to provide the best estimate of the overall uncertainty. As part of the national Explore2070 project, the present study thus aims at assessing the hierarchy of uncertainties in changes on river flow extremes at the scale of France. Amongst all possible sources of uncertainties, two are here considered: (1) the uncertainty in General Circulation Model (GCM) configuration, with 7 different models that adequately sample the range of changes as projected by the GCMs used in the IPCC AR4 over France, and (2) the uncertainty in hydrological model structure, with 2 quite different models: GR4J (Perrin et al., 2003), a lumped conceptual model, and Isba-Modcou (Habets et al., 2008), a suite of a land surface scheme and a distributed hydrogeological model. The hydrological models have been run at more than 1500 locations in France over the 1961-1990 baseline period with forcings from both the Safran near-surface atmospheric reanalysis (Vidal et al., 2010) and the GCM control runs downscaled with a weather type method (Boé et al., 2006), and over the 2046-2065 period with forcings from all downscaled GCM runs under the A1B emissions scenario. Various high flow indices (annual maximum daily flow with return period of 10 and 20 years, the daily flow value exceeded 10% of the time) and low flow indices (annual minimum monthly flow with a 5-year return period, annual minimum 10-day mean flow with a 2-year return period, the daily flow value exceeded 95% of the time) as well as seasonality indices have been computed for both periods. An analysis of variance has been performed for each river flow index and at all stations shared by the two hydrological models (around 500) in order to assess the two considered sources of uncertainties in index changes as well as their hierarchy. Results first show spatial differences in the amount of sampled uncertainties due to both sub-regional climate specificities and catchment properties. The analysis of hierarchy between climate and hydrological uncertainties show striking differences (1) over France for a single index and (2) between different indices. The part of uncertainty relative to the hydrological response for example appears to be much more important for low-flow indices than for high-flow indices. Experiments have additionally been performed to possibly reduce the overall uncertainty by weighting combinations of GCM and hydrological model through their ability of reproducing observed river flow extreme values over the baseline period. The results of this study will help to define the relevant hydrological scenarios to be used in the adaptation part of the Explore2070 project for deriving national-scale adaptation strategies
Eemian estuarine record forced by glacio-isostasy (southern Iceland)âlink with Greenland and deep sea records
International audienc
Vulnérabilité des ressources en eau au changement global en zone méditerranéenne - Le projet Vulcain. Compte-rendu de fin de projet
The Mediterranean region has been pointed out as a « hot spot » in terms of climate change, withsevere warming and precipitations decrease. Moreover, the intense population growth rate willprobably deepen its water resources structural deficit. In the future, the water scarcity level will dependon both the withdrawals and the climate evolution. The VULCAIN project proposes a method toanalyze and compare the climate and socio-economic change impacts on the water resources of thePyrĂ©nĂ©es Orientales department (figure 1). Future climate and drinking/agricultural water usescenarios have been built and their impact on the water resources of the study zone wascharacterized and compared, with a description of the associated uncertainties. The results allowedthe vulnerability characterization based on future water resources to water use budget. The mainissues of the vulnerability of the studied territory have been identified, which are currently integratedby the water managers to structure their adaptation strategies.La rĂ©gion mĂ©diterranĂ©enne est considĂ©rĂ©e comme un « hot spot » du changement climatique, affectĂ©epar une poursuite du rĂ©chauffement et une diminution des prĂ©cipitations. Par ailleurs, le rapideaccroissement dĂ©mographique observĂ© risque dâaggraver son dĂ©ficit structurel en termes deressource en eau. Dans le futur, le niveau de raretĂ© de lâeau devrait dĂ©pendre Ă la fois de lâĂ©volutiondes prĂ©lĂšvements et du climat. Le projet VULCAIN propose une mĂ©thode dâĂ©tude et de comparaisondes impacts du changement climatique et socio-Ă©conomique sur les ressources en eau sur ledĂ©partement des PyrĂ©nĂ©es Orientales (figure 1). AprĂšs avoir Ă©laborĂ© des scĂ©narios de climat etdâĂ©volution des usages eau potable et agricoles, leur impact sur les ressources en eau du territoire aĂ©tĂ© caractĂ©risĂ© Ă lâaide de modĂšles et comparĂ©, en veillant Ă identifier les sources dâincertitudes quileur sont associĂ©es. Les rĂ©sultats ont permis de caractĂ©riser la vulnĂ©rabilitĂ© en se basant sur un bilanentre ressources et usages futurs. Ce travail a permis dâidentifier les enjeux en termes de vulnĂ©rabilitĂ©sur le territoire Ă©tudiĂ© et dâalimenter les structures de gestion pour leur rĂ©flexion en termes destratĂ©gies dâadaptation
Transdisciplinary characterisation of a complex coastal aquifer, for a sustainable exploitation of its groundwater resources in a Mediterranean context. The DEM'EAUX ROUSSILLON project
International audienceMore than 80 million m3 per year are pumped into the Roussillon plain coastal aquifer, covering 850 kmÂČ and located between the Pyrenean massif to the west and the Mediterranean Sea to the east, south of France. This is a multilayer aquifer of more than 350 m thick, made up of sandy layers embedded in low-permeability clayey material from the Pliocene and topped by alluvial formations from the Quaternary. Its groundwater resource is primarily used for the supply of drinking water, but also contributes to the irrigation of some 13,000 hectares. For more than 40 years, this aquifer has been undergoing a general decline in its piezometric level due to pumping and water demand is expected to increase (growing irrigation areas and climatic demand). Moreover, given its flat topography, the Roussillon plain is likely to suffer sea water intrusions and marine submersion, due to the sea level rise, which could reach 1 m by 2100. This context shaped the Dem'Eaux Roussillon project, which brought together nearly ten partners from the Occitanie region (research units, consultancies and local authorities). Its objective was to characterise the behaviour of the groundwater resource in this aquifer, in order to be able to project its future situation, in the context of climate change, rising sea levels (risk of saline intrusion) and changes in water use. A detailed characterisation of the geological reservoir highlighted the need to consider the offshore extension of this coastal aquifer. The analysis of the piezometric evolution at the scale of the Roussillon plain over the last 50 years allowed the spatialized characterization of the hydrodynamic parameters and the understanding of the vertical drainage processes that control the hydraulic equilibrium between the Quaternary and the Pliocene water tables. Two high-resolution hydro-geophysical observatories have been set up to quantify these processes and improve understanding of saline intrusions processes. Finally, a conceptual model presenting the main features of the main processes controlling the groundwater evolution and the sea water intrusion risk was obtained ready to launch a numerical modelling wor
Transdisciplinary characterisation of a complex coastal aquifer, for a sustainable exploitation of its groundwater resources in a Mediterranean context. The DEM'EAUX ROUSSILLON project
International audienceMore than 80 million m3 per year are pumped into the Roussillon plain coastal aquifer, covering 850 kmÂČ and located between the Pyrenean massif to the west and the Mediterranean Sea to the east, south of France. This is a multilayer aquifer of more than 350 m thick, made up of sandy layers embedded in low-permeability clayey material from the Pliocene and topped by alluvial formations from the Quaternary. Its groundwater resource is primarily used for the supply of drinking water, but also contributes to the irrigation of some 13,000 hectares. For more than 40 years, this aquifer has been undergoing a general decline in its piezometric level due to pumping and water demand is expected to increase (growing irrigation areas and climatic demand). Moreover, given its flat topography, the Roussillon plain is likely to suffer sea water intrusions and marine submersion, due to the sea level rise, which could reach 1 m by 2100. This context shaped the Dem'Eaux Roussillon project, which brought together nearly ten partners from the Occitanie region (research units, consultancies and local authorities). Its objective was to characterise the behaviour of the groundwater resource in this aquifer, in order to be able to project its future situation, in the context of climate change, rising sea levels (risk of saline intrusion) and changes in water use. A detailed characterisation of the geological reservoir highlighted the need to consider the offshore extension of this coastal aquifer. The analysis of the piezometric evolution at the scale of the Roussillon plain over the last 50 years allowed the spatialized characterization of the hydrodynamic parameters and the understanding of the vertical drainage processes that control the hydraulic equilibrium between the Quaternary and the Pliocene water tables. Two high-resolution hydro-geophysical observatories have been set up to quantify these processes and improve understanding of saline intrusions processes. Finally, a conceptual model presenting the main features of the main processes controlling the groundwater evolution and the sea water intrusion risk was obtained ready to launch a numerical modelling wor