From global climate models to local water stress: A framework for estimating future water availability in the Mediterranean

Study region: River basins draining into the Mediterranean Sea (excluding the Nile). The study area covers approximately 1.5 million km2 across Southern Europe, North Africa, and the Near East, supporting around 200 million inhabitants. Study focus: The objective is to assess potential water availability in Mediterranean basins under historical and future climate scenarios. Climate and runoff projections from the Inter-Sectoral Impact Model Intercomparison Project (ISIMIP3b) are combined with global hydrological models (H08 and CWatM) to simulate natural flows. The Water Availability and Adaptation Policy Analysis (WAAPA) model is used to incorporate reservoir operations, ecological flows, and demand reliability. Potential water availability is defined as the maximum demand that can be satisfied under specified management rules. The analysis considers three climate and socioeconomic scenarios (SSP1-2.6, SSP3-7.0 and SSP5-8.5) over two future time horizons (2020-2059 and 2060-2099). New hydrological insights for the region: Results show a projected reduction of up to 26 % in annual flows and up to 41 % in potential availability by 2100 under high-emission scenarios. Reservoirs currently provide over 50 % of available water, buffering seasonal and interannual variability, yet increasing climate variability and population growth will exacerbate water stress. The study identifies spatial hotspots of future scarcity and emphasizes the need for basin-scale adaptation strategies and integrated management of surface, groundwater, and non-conventional water resources across the Mediterranean region.