Future Mediterranean drying: The role of stationary eddies

We investigate changes in the Mediterranean hydroclimate using historical simulations and future projections from ten models participating in phase 6 of the Coupled Model Intercomparison Project (CMIP6) through the lens of the atmospheric moisture budget. By the end of the 21st century, the multi-model mean projects a substantial decrease in annual-mean net precipitation ($P-E$) over the Mediterranean Sea and surrounding land. This primarily arises from increased moisture flux divergence by the time-mean flow, while changes in transient eddies make a smaller and more spatially heterogeneous contribution. Decomposing the time mean flow into contributions from the zonal mean and stationary eddies reveals that much of the annual-mean response is associated with changes in stationary eddies, rather than with the zonal-mean overturning circulation. The dominant stationary-eddy drying tendency arises from increased moisture divergence by the zonally anomalous circulation acting on zonal-mean moisture and is associated with enhanced zonally anomalous descent over the Mediterranean. This tendency is partially compensated by changes in the pure stationary-eddy term, reflecting the coupling between zonally anomalous circulation and moisture. Both thermodynamic and circulation changes contribute to the projected drying, although their relative importance varies seasonally: circulation changes play a more prominent role in the localized winter response, whereas thermodynamic changes make a larger contribution to summertime time-mean drying. Our results highlight the importance of zonally asymmetric circulation changes, alongside thermodynamic changes, in shaping the magnitude and spatial structure of future Mediterranean hydroclimate change.