Water resources planning and climate change adaptation strategies of Sardinian basins under water-limited conditions

Sardinia, an island in the western Mediterranean Sea, serves as a natural laboratory to study the effects of climate change on ecosystems and water resources in water-limited environments. Long-term observations over the last century have revealed significant declines in winter precipitation, a halving of annual river runoff, and an increase of approximately 1 °C in mean annual air temperature. To investigate ecosystem responses to contrasting precipitation regimes, two micrometeorological towers were installed: one in Orroli, a site characterized by shallow basaltic soils, herbaceous vegetation, and wild olive trees; and another in the Marganai forest, a denser holm oak (Quercus ilex) forest on steeper rocky slopes. Measurements of land surface energy fluxes, carbon dioxide fluxes, soil moisture, and tree transpiration highlight different ecohydrological behaviors: at Orroli, evapotranspiration (ET) closely follows seasonal rainfall patterns and vegetation dynamics, whereas at Marganai, ET remains more stable throughout the year, sustained by deep water sources accessed by the trees. Ecohydrological models, coupled with climate projections from IPCC global circulation models, predict that rising temperatures and decreasing precipitation will lead to further reductions in vegetation cover (with up to a 50% decrease in Leaf Area Index), tree transpiration, and water availability. Future scenarios for 2024–2100 forecast that irrigation demands will not be fully satisfied, with up to 74% of future years experiencing irrigation deficits, and an average deficit of up to 52%. Additionally, although annual runoff is expected to decrease, the severity of flood events may increase, highlighting a future that is both drier and more prone to extreme events. These findings underscore the vulnerability of Sardinian ecosystems and water resource systems to climate change, emphasizing the urgent need for adaptive water and land management strategies to ensure the island’s environmental and economic sustainability under future climate conditions.