Guiding national water resource policies: An example of estimating potential water stress in France in 2050.

The risk of water scarcity is increasing with climate change, even in countries with significant water resources such as France. Over the past 10 years, French governments and public agencies have implemented public policies to adapt to climate change. Identifying and quantifying stress on water resources is essential for developing effective public policies. Our objectives were therefore to estimate the potential stress on surface water resources in 2050 under three demand scenarios. At the watershed level, the environmental flow requirement, water needs for all human activities (agriculture, industry, energy production, etc.), and future water resources were compared on a monthly basis for a year with high rainfall and a year with low rainfall in the spring and summer. Two climate change projections were considered (with the RCP8.5 and the biais correction ADAMONT) : HadGEM2-ES/CCLM4-8-17 and CNRM-CM5/ALADIN63. The environmental flow requirement was estimated from the variable monthly flow method. The water demand of human activities were estimated using the latest climate projections and an integrated water resource management tool. Future water resources were estimated based on the results of the EXPLORE2 project, which provides daily projections of the flow of France's main rivers, using two hydrological model : ORCHIDEE and SMASH. Three demand scenarios were considered: the “trend” scenario continues past trends, the “public policies” scenario takes into account changes in water demand for certain activities, and the “disruptive” scenario envisages a water-efficient society. This study is the first national-scale study to estimate potential water stress in 2050, taking into account all human activities. Main results are : (i) Under both climate projections considered, for 93% of the watersheds, envrionmental flow requirement would not be satisfied for at least one month of the year in dry years (low rainfall during spring and summer), (ii) under the HadGEM2-ES/CCLM4-8-17 climate projection, water consumption will increase in 2050 in all scenarios, (iii) a dry year could lead to severe water stress across 88% of the country, and water restrictions would need to be enforced and (iv) only a public policy similar to the « disruptive » scenario could mitigate the increase in water stress.