Large-scale, inter-annual relations among surface temperature, water vapour and precipitation with and without ENSO and volcano forcings

摘要

How the global hydrological cycle, generally denoted by precipitation, responds to surface temperature change has been debated for decades. This debate is crucial to correctly assess the global warming-related climate variability/change in the water cycle, but reflects our limited understanding of the relationships that exist among key components of the water cycle on various spatial and temporal scales. Primarily using satellite-based measurements, we find that correlations between precipitation and surface temperature anomalies averaged over large domains (i.e. tropical and global ocean/land areas) during 1988-2008 are very weak once the effects from two large-scale forcings, ENSO and volcanic eruptions, are removed, whereas tropospheric water vapour content varies with surface temperature no matter whether the ENSO and volcanic effects are included or not. We thus conclude that precipitation variability on the inter-annual time scale, once the net large-scale dynamic effects particularly associated with ENSO become weak or limited, does not follow surface temperature and related water vapour variations, even though inter-decadal signals may still exist. This is consistent with the fact that ENSO precipitation signals are usually weak over combined land plus ocean areas for both tropical and global regimes, though ENSO can greatly modulate global precipitation patterns through shifting large-scale circulation systems. These findings are also similar to the weak global-mean precipitation responses under the recent global warming that have been evident in both observations and models, compared to large associated tropospheric water vapour changes, roughly following the Clausius-Clapeyron (CC) relation.