Water availability assessment across Southern Italy under future climate scenarios

Assessing the impact of climate change on water availability requires robust and spatially consistent modelling frameworks, particularly in Mediterranean regions characterized by strong hydroclimatic variability. The Mediterranean basin is widely recognized as a climate-change hotspot, where increasing temperatures and changes in precipitation regimes are expected to exacerbate water scarcity and hydrological extremes, especially in southern areas (Lazoglou et al., 2024). This study investigates future water availability across Southern Italy, with a specific focus on the Southern Apennines River Basin District, by coupling high-resolution climate projections with a large-scale gridded hydrological model.

Future climate forcing was derived from the Global Climate Model MPI-ESM-1-2-HR under the SSP5-8.5 scenario and dynamically downscaled at a convection-permitting scale (~4 km) using the WRF model. Bias-corrected precipitation and air temperature fields were subsequently re-gridded to 1-km resolution and used to force HYGRID-M (an acronym for HYdrological GRIDed – Monthly), a distributed water balance model operating at monthly time scale. HYGRID-M simulates actual evapotranspiration and runoff by integrating climatic inputs with spatially distributed information on land use, soil properties, and topography. The modelling framework was applied to simulate water balance components for the future period 2025–2044 and compared with a observed baseline (2000–2023), analyzing changes in precipitation seasonality and temperature, together with their impacts on evapotranspiration and runoff at both temporal and spatial scales.

Results indicate a marked reduction in summer precipitation and a consistent increase in air temperature across all months, with warming reaching approximately +2°C. Despite higher temperatures, both actual evapotranspiration and runoff exhibited predominantly negative anomalies relative to the observed period, reflecting increased water limitations rather than a persistent long-term decreasing trend. Actual evapotranspiration (AET) exhibited yearly variations ranging from -29% to +16% with a mean of -2% and a standard deviation of 10.2% while runoff (Q) ranged from –39% to +46%, with a mean of –1.3% and a standard deviation of 24%, indicating the strong interannual variability with alternating dry and wetter years. The negligible contribution of snow accumulation and melting under future climatic conditions further alters seasonal runoff dynamics. Spatially, evapotranspiration responses were heterogeneous, with localized increases in Puglia and parts of Basilicata, whereas runoff showed mixed signals, with widespread reductions across Campania, Molise, Abruzzo and parts of Calabria.

Overall, the results highlight a shift toward drier and more variable hydroclimatic conditions in Southern Italy, emphasizing the importance of integrated high-resolution climate–hydrological modelling for supporting climate adaptation and sustainable water resource planning at river basin scale.