Divergent Changes in Oceanic and Terrestrial Surface Water Budgets Under Global Warming: Insights From ERA5 Reanalysis

Abstract Understanding how the global surface water budget (WB) responds to climate warming is crucial for assessing future water resources and hydroclimatic extremes. Here, we develop a process‐level decomposition framework and apply it to ERA5 reanalysis (1981–2024) to quantify WB sensitivity to global mean surface temperature (GMST). WB changes are regressed against GMST and decomposed into thermodynamic, mean‐circulation, transient‐eddy, surface‐pressure and column‐storage contributions, using vertically integrated water vapor divergence (VIWVD) as a closure‐consistent diagnostic. Results suggest an intensification of the water cycle: enhanced ocean moisture export and increased land moisture convergence imply strengthened ocean‐to‐land moisture redistribution. Circulation and transient‐eddy largely shape the spatial WB response, while net thermodynamic effects are secondary due to compensating subcomponents. Regime analysis shows circulation‐driven drying in subtropical/deficit zones and thermodynamic‐ and eddy‐driven wetting in surplus/high‐latitude zones, and weak net changes in transitional regions. Beyond quantifying mechanisms, our framework provides a transferable diagnostic tool for assessing model and reanalysis performance and for contextualizing regional water cycle changes under warming.