Understanding the uncertainty in the climate and water resource availability interplay: a distributed analysis of the Italian territory

As the tangible impacts of climate change continue to unfold, the imperative to assess and prepare for its repercussions on water resources becomes increasingly evident. This study addresses the urgent necessity to foresee future scenarios of surface water availability in Italy, recognizing the crucial role of water in sustaining ecosystems, agriculture, and human life. To unravel the intricate interplay between climate change and water availability, our methodology integrates the three representative concentration pathways (RCPs) from the Intergovernmental Panel on Climate Change with six regional circulation models. This combination projects future trajectories of temperature and precipitation. Utilizing the time-varying quantile mapping downscaling technique, we refine these trajectories for enhanced spatial and temporal resolution (1 km). These downscaled data feed into the water balance model BIGBANG, developed by the Italian Institute for Environmental Protection and Research (ISPRA), facilitating the generation of the spatiotemporal distributions of surface water availability across Italy. A probabilistic analysis offers a nuanced understanding of potential future water scenarios. Our findings highlight the profound influence of emission scenarios on water availability's future trajectory. Under maximum adaptation conditions (RCP 2.6), a relatively stable water availability pattern is projected through the century. Conversely, the business-as-usual scenario predicts a significant decrease of up to 50% in surface water availability, particularly in historically drought-prone southern regions of the country. These results underscore the critical importance of proactive adaptation measures to mitigate the potential impacts of climate change on Italy's water resources.