The Response of Precipitation Minus Evapotranspiration to Climate Warming: Why the “Wet-Get-Wetter, Dry-Get-Drier” Scaling Does Not Hold over Land

The Response of Precipitation Minus Evapotranspiration to Climate Warming: Why the “Wet-Get-Wetter, Dry-Get-Drier” Scaling Does Not Hold over Land

Simulations with climate models show a land–ocean contrast in the response ofP – E(precipitation minus evaporation or evapotranspiration) to global warming, with larger changes over ocean than over land. The changes over ocean broadly follow a simple thermodynamic scaling of the atmospheric moisture...

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Bibliographic Details
Published in:Journal of climate 2015-10, Vol.28 (20), p.8078-8092
Main Authors: Byrne, Michael P., O’Gorman, Paul A.
Format: Article
Language:eng
Subjects:
Atmospheric moisture
Climate change
Climate models
Drying
Global warming
Humidity
Hydrologic cycle
Land
Marine
Oceans
Precipitation
Relative humidity
Salinity
Temperature gradients
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Summary:Simulations with climate models show a land–ocean contrast in the response ofP – E(precipitation minus evaporation or evapotranspiration) to global warming, with larger changes over ocean than over land. The changes over ocean broadly follow a simple thermodynamic scaling of the atmospheric moisture convergence: the so-called “wet-get-wetter, dry-get-drier” mechanism. Over land, however, the simple scaling fails to give any regions with decreases inP – E, and it overestimates increases inP – Ecompared to the simulations. Changes in circulation cause deviations from the simple scaling, but they are not sufficient to explain this systematic moist bias. It is shown here that horizontal gradients of changes in temperature and fractional changes in relative humidity, not accounted for in the simple scaling, are important over land and high-latitude oceans. An extended scaling that incorporates these gradients is shown to better capture the response ofP – Eover land, including a smaller increase in global-mean runoff and several regions with decreases inP – E. In the zonal mean over land, the gradient terms lead to a robust drying tendency at almost all latitudes. This drying tendency is shown to relate, in part, to the polar amplification of warming in the Northern Hemisphere, and to the amplified warming over continental interiors and on the eastern side of midlatitude continents.
ISSN:0894-8755
1520-0442