Geoscience Reference
In-Depth Information
Physically Consistent Responses of the Global
Atmospheric Hydrological Cycle in Models
and Observations
Richard P. Allan
Chunlei Liu
Matthias Zahn
David A. Lavers
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Evgenios Koukouvagias
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Alejandro Bodas-Salcedo
Received: 30 August 2012 / Accepted: 6 November 2012 / Published online: 10 January 2013
Springer Science+Business Media Dordrecht 2013
Abstract Robust and physically understandable responses of the global atmospheric water
cycle to a warming climate are presented. By considering interannual responses to changes in
surface temperature (T), observations and AMIP5 simulations agree on an increase in column
integrated water vapor at the rate 7 %/K (in line with the Clausius-Clapeyron equation) and
of precipitation at the rate 2-3 %/K (in line with energetic constraints). Using simple and
complex climate models, we demonstrate that radiative forcing by greenhouse gases is
currently suppressing global precipitation (P)at*-0.15 %/decade. Along with natural
variability, this can explain why observed trends in global P over the period 1988-2008 are
close to zero. Regional responses in the global water cycle are strongly constrained by
changes in moisture fluxes. Model simulations show an increased moisture flux into the
tropical wet region at 900 hPa and an enhanced outflow (of smaller magnitude) at around
600 hPa with warming. Moisture transport explains an increase in P in the wet tropical
regions and small or negative changes in the dry regions of the subtropics in CMIP5 sim-
ulations of a warming climate. For AMIP5 simulations and satellite observations, the
heaviest 5-day rainfall totals increase in intensity at *15 %/K over the ocean with reduc-
tions at all percentiles over land. The climate change response in CMIP5 simulations shows
consistent increases in P over ocean and land for the highest intensities, close to the Clau-
sius-Clapeyron scaling of 7 %/K, while P declines for the lowest percentiles, indicating that
interannual variability over land may not be a good proxy for climate change. The local
changes in precipitation and its extremes are highly dependent upon small shifts in the large-
scale atmospheric circulation and regional feedbacks.
Keywords
Precipitation
Water
Climate models
Satellite data
Global change
