The Mediterranean basin has been identified as one of the world's regions most vulnerable to climatic and anthropogenic changes. A methodology accounting for the basin specific conditions is developed to assess the impacts of these changes on water resources. Based on global climate projections and water-use scenarios inspired by national reports, the current water stress state is addressed first and then it is explored for the mediumterm. Currently, the southern and eastern rims are experiencing high to severe water stress. By the 2050 horizon, this stress could increase over the whole Mediterranean basin, notably because of a 30-50% decline in freshwater resources as a result of climate change. In addition, under a business-as-usual water-use scenario, total water withdrawals are projected to double on the southern and eastern rims. These worrying trends indicate the need to develop mitigation scenarios. In accord with the Mediterranean Strategy for Sustainable Development, an alternative water-use scenario based on improvements in the efficiency of water distribution networks and of irrigated agriculture is investigated. Such progress would stabilize total water withdrawals over the Mediterranean basin and even make them decrease (10-40%) in many northern catchments. Water stress could thus be tempered in some eastern catchments and remain low on the northern rim. This study highlights the importance of developing sustainable development strategies to cope with climatic and anthropogenic changes in order to explore their impacts at regional scales. It supports the need to focus on the most vulnerable areas within the Mediterranean basin. Key words regional assessment; water stress index; climate scenarios; water-use scenarios; sustainable development strategies; Mediterranean basin Etat actuel des ressources en eau en Méditerranée et tendances futures sous contraintes de changements climatiques et anthropiques Résumé Le bassin méditerranéen a été identifié comme l'une des régions au monde les plus vulnérables aux changements climatiques et anthropiques. Une méthode intégrant les spécificités du bassin a été développée afin d'évaluer les impacts de ces changements sur les ressources en eau. Elle s'appuie sur des projections climatiques globales et des scénarios d'usages de l'eau, définis à partir de rapports nationaux, pour évaluer l'état actuel du stress hydrique et son évolution à moyen terme. Actuellement, le sud et l'est de la méditerranée doivent faire face à un stress hydrique sévère, voire à des pénuries d'eau. D'ici 2050, le stress hydrique pourrait augmenter sur l'ensemble du pourtour méditerranéen, en particulier du fait d'une diminution de 30 à 50 % des ressources en eau associée aux changements climatiques. De plus, selon un scénario d'usages de l'eau tendanciel, les prélèvements totaux en eau pourraient doubler sur les rives sud et est de la Méditerranée. Ces tendances suggèrent le besoin de développer des scénarios alternatifs. En se fondant sur la Stratégie Méditerranéenne pour le Développement D...

No abstract

Abstract. In this study we present an integrative modeling framework aimed at assessing the balance between water demand and availability and its spatial and temporal variability over long time periods. The model was developed and tested over the period 1971-2009 in the Hérault (2500 km 2 , France) and the Ebro (85 000 km 2 , Spain) catchments. Natural streamflow was simulated using a conceptual hydrological model. The regulation of river flow was accounted for through a widely applicable demand-driven reservoir management model applied to the largest dam in the Hérault Basin and to 11 major dams in the Ebro Basin. Urban water demand was estimated from population and monthly unit water demand data. Water demand for irrigation was computed from irrigated area, crop and soil data, and climatic forcing. Water shortage was assessed at a 10-day time step by comparing water demand and availability through indicators calculated at strategic resource and demand nodes. The outcome of this study is twofold. First, we were able to correctly simulate variations in influenced streamflow, reservoir levels and water shortage between 1971 and 2009 in both basins, taking into account climatic and anthropogenic pressures and changes in water management strategies over time. Second, we provided information not available through simple data analysis on the influence of withdrawals and consumptive use on streamflow and on the drivers of imbalance between demand and availability. Observed past variations in discharge were explained by separating anthropogenic and climatic pressures in our simulations: 3 % (20 %) of the decrease in the Hérault (Ebro) discharge were linked to anthropogenic changes. Although key areas of the Hérault Basin were shown to be highly sensitive to hydro-climatic variability, the balance between water demand and availability in the Ebro Basin appears to be more critical, owing to high agricultural pressure on water resources. The modeling framework developed and tested in this study will be used to assess water balance under climatic and socioeconomic prospective scenarios and to investigate the effectiveness of adaptation policies aimed at maintaining the balance between water demand and availability.