Abstract
Large-scale modes of climate variability (or teleconnection patterns), such as the El Niño Southern Oscillation and the North Atlantic Oscillation, affect local weather worldwide. However, the response of terrestrial water and energy fluxes to these modes of variability is still poorly understood. Here, we analyse the response of evaporation to 16 teleconnection patterns, using a simple supervised learning framework and global observation-based datasets of evaporation and its key climatic drivers. Our results show that the month-to-month variability in terrestrial evaporation is strongly affected by (coupled) oscillations in sea-surface temperature and air pressure: in specific hotspot regions, up to 40% of the evaporation dynamics can be explained by climate indices describing the fundamental modes of climate variability. While the El Niño Southern Oscillation affects the dynamics in land evaporation worldwide, other phenomena such as the East Pacific–North Pacific teleconnection pattern are more dominant at regional scales. Most modes of climate variability affect terrestrial evaporation by inducing changes in the atmospheric demand for water. However, anomalies in precipitation associated to particular teleconnections are crucial for the evaporation in water-limited regimes, as well as in forested regions where interception loss forms a substantial fraction of total evaporation. Our results highlight the need to consider the concurrent impact of these teleconnections to accurately predict the fate of the terrestrial branch of the hydrological cycle, and provide observational evidence to help improve the representation of surface fluxes in Earth system models.
Highlights
Intra-annual and decadal variability in Earth’s climate is largely driven by large-scale and periodic changes in the state of ocean and atmosphere, such as the El Niño Southern Oscillation (ENSO)
Key climatic drivers of terrestrial evaporation, such as precipitation, total incoming radiation and near-surface air temperature, are known to be affected by different teleconnection patterns. This effect is likely to propagate to the dynamics in land evaporation.[4]
Clear hotspots, where up to 40% of the variance in land evaporation can be explained by the climate indices (CIs) can be identified for different seasons (Fig. 1b)
Summary
Intra-annual and decadal variability in Earth’s climate is largely driven by large-scale and periodic changes in the (coupled) state of ocean and atmosphere, such as the El Niño Southern Oscillation (ENSO) These modes of climate variability do affect meteorological conditions in regions where they occur, but can influence weather patterns in remote areas, being commonly referred to as teleconnections.[1] As such, these modes of climate variability are expected to affect the general dynamics of ecosystems and biogeochemical cycles inland.[2,3] Terrestrial evaporation (or evapotranspiration) is a critical variable in the water cycle that can serve as a diagnostic of ecosystem activity, and that is expected to be influenced by these teleconnections.[4] Terrestrial evaporation consists of the vaporization of water through vegetation (transpiration), directly from soil (bare soil evaporation), or from wet canopies (interception loss) and snowcovered surfaces (sublimation). Transpiration accounts for the vast majority of the flux at the continental scale,[5] and is closely related to the process of photosynthesis—the assimilation of carbon dioxide by plants—acting as a nexus between the water and carbon cycles.[6,7] Due to the high energy requirements to evaporate water, terrestrial evaporation controls the partitioning of radiation at the ecosystem and the cycling of energy in the atmosphere, thereby affecting air temperature, humidity and cloud formation.[8,9,10,11]
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