Eastern Mediterranean Drying: Projected Changes in Dynamics and Thermodynamics and Their Relation to Large-Scale Processes

Observations from the past century and projections for the end of this century show a decrease in precipitation over the eastern Mediterranean Sea and surrounding land areas. Changes in precipitation are controlled by both thermodynamic and dynamic processes, but the relative contributions of these processes, in particular on regional scales, is not well understood. Models included in the fifth and sixth phases of the Coupled Model Intercomparison Project (CMIP5 and CMIP6) exhibit a wide spread in the magnitude of expected drying in the eastern Mediterranean region, as well as in other meteorological variables. By decomposing projected changes in the moisture budget in 48 models into mean dynamic and mean thermodynamic components, we explore the contribution of each of these components to the model spread in regional drying. In the eastern Mediterranean, the dynamic component explains 64% and the thermodynamic component explains 9% of the variance in net precipitation change. We further examine the relation of the regional components to changes in five large-scale mechanisms: tropical vertical stratification, global near-surface temperature, latitude of the eddy-driven jet, stratospheric polar vortex, and arctic amplification. Of these, we find that a decrease in the dynamical contribution in the eastern Mediterranean, causing regional drying, is most strongly related to a northward shift of the eddy-driven jet and a rise in global near-surface temperature.