Hydrological Sustainability of Dam-Based Water Resources in a Mediterranean Basin Undergoing Climate Change

The Flumendosa dams are a key part of the water resources system of the island of Sardinia. The analysis of a long-term (1922–2022) hydrological database showed that the Flumendosa basin has been affected by climate change since the middle of the last century, associated with a decrease in winter precipitation and annual runoff (Mann–Kendall τ = −0.271), reduced by half in the last century, and an increase in the mean annual air temperature (Mann–Kendall τ = +0.373). We used a spatially distributed ecohydrological model and a water resources management model (WARGI) to define the economic efficiency and the optimal water allocation in the water system configurations throughout the evaluation of multiple planning and management rules for future climate scenarios. Using future climate scenarios, testing land cover strategies (i.e., forestation/deforestation), and optimizing the use of water resources, we predicted drier future scenarios (up to the end of the century) with an alarming decrease in water resources for agricultural activities, which could halt the economic development of Sardinia. In the future hydrological conditions (2024–2100), irrigation demands will not be totally satisfied, with up to 74% of future years being in deficit for irrigation, with a mean deficit of up to 52% for irrigation.