Changing moisture transport as a driver of continental drying

Land available water has declined across many regions over recent decades, reflecting widespread aridification and increasing pressure on terrestrial systems. These changes are commonly attributed to shifts in precipitation, enhanced evaporative demand, and increasing soil moisture limitations under warming. However, the extent to which changes in large-scale atmospheric moisture transport contribute to declining continental water availability remains poorly understood. 

To address this gap, we develop a four-decade (1979–2024) global dataset of atmospheric trajectories based on the Lagrangian transport model FLEXPART driven by ERA5 data, and evaluate the atmospheric moisture transport using a novel attribution framework. This framework allows us to link changes in the continental water balance (P–E) to shifts in moisture source–sink relationships, including continental evaporation recycling, defined as the fraction of land evaporation that returns as precipitation over land.  

Our results show that the declining continental P–E is associated with a relative decrease of evaporation recycling and a relative increase in the export of land-evaporated moisture towards the oceans.  These changes cannot be directly explained by changes in terrestrial evaporation. Instead, they respond to changes in large-scale circulation, together with reduced precipitation efficiency and longer atmospheric residence times. 

These results demonstrate that thermodynamic and dynamical changes in atmospheric moisture transport provide a missing link between observed P–E declines and continental aridification, with important implications for future land water availability.