Changes of Water Vapor Budget over East Asia in Response to 4xCO2 Concentration Forcing

Water resources are essential for the economic development and social security in East Asia, especially under global warming. Based on newly released CMIP6 149-year simulation data from a pre-industrial control experiment (piControl) and a forced experiment on the abrupt quadrupling of CO2 concentration (abrupt-4xCO2), changes of water vapor budget over East Asia due to 4xCO2 concentration forcing and their possible mechanisms are investigated. Change of precipitation (P) demonstrates a spatial pattern of “Southern Flood and Northern Drought” (SFND) in eastern China, which can also be seen in the change of evaporation (E), though at a much smaller amplitude. The change of water vapor budget represented by E–P is dominated by P, which is primarily induced by changes of water vapor divergence associated with both moisture-related thermodynamic contribution and atmospheric circulation-related dynamic contribution. Specifically, under global warming, tropical El Nino-like SST warming causes weakened Walker circulation through decreased zonal temperature gradient, while amplified Arctic warming induces a negative Arctic Oscillation pattern via reduced meridional temperature gradient. The combined signals from tropical and mid-high latitudes result in significant long-term changes of water vapor convergence as well as much more precipitation in the Yangtze River Valley, forming the SFND. Furthermore, the intensity of the SFND change pattern could also have notable interdecadal variation, which is mainly attributed to the modulation of interdecadal signals of the Indian Ocean basin mode (IOBM) and Pacific Decadal Oscillation (PDO). Results of this study could provide an important scientific basis for the future planning and management of water resources over East Asia, specifically in eastern China.