Atmospheric moisture dynamics: a precipitationshed and evaporationshed analysis across Italy

Human activities have determined deep changes in the global water cycle, with significant effects on the availability and quality of hydrological resources. This study investigates the dynamics of atmospheric moisture and hydrological connectivity in Italy and in three regions (Piemonte, Lazio, Sicily) through the analysis of two main concepts: evaporationsheds – that is, the downwind areas where the precipitations supplied by the evaporation in the region of interest occur – and precipitationsheds – that is, the upwind areas from which the evaporation contributing to precipitations in the region of interest originates. The study has been implemented through the use of two different datasets: UTrack – a Lagrangian atmospheric moisture tracking model developed by Tuinenburg et al. (2020) – and RECON, a post-processed version of UTrack. Both datasets allowed for the reconstruction of the annual atmospheric moisture forward and backward flows relative to the regions of interest. While UTrack provided a detailed analysis on both an annual and seasonal scale, RECON focused only on annual flows. The comparative analysis between the outputs of the two datasets highlights a better consistency of RECON, which shows greater uniformity with ERA5 data and better adherence to the principle of mass conservation. Italy emerges as an evident ‘atmospheric bridge,’ receiving most of its precipitations from moisture coming from the west, particularly from the North Atlantic Ocean, and redistributing this water mainly towards the east, reaching far areas such as Russia. The quantitative analysis, based on RECON data, highlights that 92.59% of Italian precipitations come from external sources to the country, while 87.72% of the water evaporating from the national territory is transported beyond the Italian territory. This trend points out a clear condition of hydrological interdependency, challenging any possible claims of water autarchy. This study, the first one realized in Italy, provides an innovative perspective regarding water management policies and adaptation to climate change, highlighting the strong interconnection bewteen different areas of the world and the importance of a global approach in water conservation.