Historical reconstruction and 2050 projections of water demand under anthropogenic and climate changes in two contrasted Mediterranean catchments

- Our integrative framework simulates spatial and temporal variations in water demand.
- Our method was validated in two catchments facing contrasted human pressures.
- We identified the main drivers of water demand and their past dynamics.
- Water use scenarios were built based on these drivers and local projections.
- Increasing human activities have more impact on water demand than climatic changes.

SummaryThis paper presents an integrative conceptual framework developed to simulate the spatial and temporal dynamics of water demand caused by human influences and climate change, at the river basin management scale. The past dynamics of urban, agricultural, and industrial components of water demand were simulated at a 10-day time step for the period between 1970 and 2009. The same model was used to forecast water demand at the 2050 horizon under water use scenarios based on local projections, trends observed in the past, and climate scenarios. Climate prediction uncertainties were taken into account using a wide range of climate scenarios downscaled from 9 IPCC-AR5 GCMs under RCP8.5. To test how widely and easily our approach can be applied, we tested it in two river basins facing different kinds of human pressure and different water management issues: the Herault basin (2500 km2) in France and the Ebro basin (85,000 km2) in Spain. Results showed that water demand has increased significantly in the last 40 years in both the Herault basin (+29%) and the Ebro basin (+57%), and revealed spatially heterogeneous variations in water demand. Identifying the main drivers of water demand and their past dynamics enabled us to build water use trend scenarios at the 2050 horizon. Simulations of water demand under anthropogenic and climate trends in 2050 revealed a significant increase in total water demand in both basins (Herault +38% to +50%, Ebro +35% to +58%). These projections show that changes in the pressure of human activities will influence variations in water demand more than climate change. The broader aim of this research is to assess the balance between water demand and supply through a comprehensive modeling framework to evaluate the sustainability of water uses in a changing environment.