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, Côte d’Ivoire, 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 Lego® 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 Bagré 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 The economic value of each m3 withdrawn to develop irrigated agriculture upstream of the basin is thus higher than that of each m3 turbined in the Akosombo-Kpong complex.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

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 rivières observée au cours des dernières 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'accès aux ressources. Le projet de recherche ANR-VULCAIN a comparé les impacts des changements climatique et socio-économique sur les hydrosystèmes du territoire des Pyrénées Orientales. Un couplage de méthodes de prospective participative et de modélisation ont été utilisés pour quantifier l'évolution des prélèvements en eau sous l'effet de ces changements. Des scénarios socio-économiques ont été construits avec les acteurs du territoire, lors de séances thématiques de travail en groupe (urbanisme et aménagement du territoire d'une part et agriculture d'autre part), dont les résultats ont été quantifiés à l'aide de modèles pour en estimer les effets des changements anthropiques sur les prélèvements domestiques et agricoles. En parallèle, des scénarios climatiques ont été utilisés dans le même modèle agricole afin d'estimer les possibles impacts des changements climatiques sur les besoins agricoles. Dans les scénarios envisagés, l'évolution des besoins nets en irrigation sous l'effet des changements anthropiques a une amplitude plus grande que l'évolution des prélèvements pour l'eau potable ou les évolutions des besoins nets en irrigation sous l'effet du changement climatique qui sont du même ordre de grandeur. Des marges de manœuvre existent pour satisfaire l'augmentation de ces besoins, en révisant les modes de distribution actuels pour les rendre plus efficients, en optimisant l'utilisation des capacités de stockage, ou en utilisant des ressources de substitution. Cet article présente l'approche utilisée, ainsi que quelques-uns des principaux résultats

Composer avec l’invisible, l’incertain et le flou des frontières : les gestionnaires interprètes des chercheurs pour planifier la gestion des aquifères 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 d’un exercice prospectif sur les impacts des changements climatiques à l’échelle nationale pour définir des stratégies d’adaptation ?

Les changements climatiques projetés à l’horizon du milieu du XXIe siècle pourraient avoir des impacts importants sur la disponibilité en eau en France. L’étude prospective Explore 2070, pilotée par le ministère chargé de l’écologie, a ainsi mis en évidence la nécessité de quantifier et d’anticiper ces changements, et de construire des stratégies d’adaptation pour limiter leurs conséquences négatives sur les hydrosystèmes et les activités humaines. Cet article analyse dans quelle mesure ces travaux ont pu contribuer à la sensibilisation des acteurs de l’eau et à la réflexion sur l’adaptation au changement climatique en France

Incertitudes climatiques et hydrologiques sur les projections de crues et d'étiages 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)—link 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 thePyrénées 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 région méditerranéenne est considérée comme un « hot spot » du changement climatique, affectéepar une poursuite du réchauffement et une diminution des précipitations. Par ailleurs, le rapideaccroissement démographique observé risque d’aggraver son déficit structurel en termes deressource en eau. Dans le futur, le niveau de rareté de l’eau devrait dépendre à la fois de l’évolutiondes prélèvements et du climat. Le projet VULCAIN propose une méthode d’étude et de comparaisondes impacts du changement climatique et socio-économique sur les ressources en eau sur ledépartement des Pyrénées Orientales (figure 1). Après avoir élaboré des scénarios de climat etd’évolution des usages eau potable et agricoles, leur impact sur les ressources en eau du territoire aété caractérisé à l’aide de modèles et comparé, en veillant à identifier les sources d’incertitudes quileur sont associées. Les résultats ont permis de caractériser la vulnérabilité en se basant sur un bilanentre ressources et usages futurs. Ce travail a permis d’identifier les enjeux en termes de vulnérabilitésur le territoire étudié et d’alimenter les structures de gestion pour leur réflexion en termes destratégies d’adaptation

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 km² 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 km² 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 km² 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