Articles | Volume 19, issue 3
Research article
05 Mar 2015
Research article |  | 05 Mar 2015

Simulating past changes in the balance between water demand and availability and assessing their main drivers at the river basin scale

J. Fabre, D. Ruelland, A. Dezetter, and B. Grouillet

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 km2, France) and the Ebro (85 000 km2, 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.

Short summary
Socioeconomic and hydro-climatic data were used to model water resources, water demand and their interactions in two river basins. By using an integrative framework we successfully modeled variations in water stress over the past 40 years, accounting for climate and human pressures and changes in water management strategies over time. We explained past changes in discharge by separating human and hydro-climatic trends. This work will help assess future water stress and design adaptation plans.