A Recent Systematic Increase in Vapor Pressure Defcit over Tropical South America




Nature Research – Scientific Reports

Armineh Barkhordarian (1,2)*, Sassan S. Saatchi (2,3),

Ali Behrangi (4) PaulC. Loikith (5) & Carlos R. Mechoso (1)

[/vc_column_text][/vc_column][/vc_row][vc_row][vc_column][vc_column_text]We show a recent increasing trend in Vapor Pressure Defcit (VPD) over tropical South America in dry
months with values well beyond the range of trends due to natural variability of the climate system
defned in both the undisturbed Preindustrial climate and the climate over 850–1850 perturbed with
natural external forcing. This trend is systematic in the southeast Amazon but driven by episodic
droughts (2005, 2010, 2015) in the northwest, with the highest recoded VPD since 1979 for the
2015 drought. The univariant detection analysis shows that the observed increase in VPD cannot be
explained by greenhouse-gas-induced (GHG) radiative warming alone. The bivariate attribution analysis
demonstrates that forcing by elevated GHG levels and biomass burning aerosols are attributed as key
causes for the observed VPD increase. We further show thatThere is a negative trend in evaporative
fraction in the southeast Amazon, where lack of atmospheric moisture, reduced precipitation together
with higher incoming solar radiation (~7% decade−1 cloud-cover reduction) infuences the partitioning
of surface energy fuxes towards less evapotranspiration. The VPD increase combined with the decrease
in evaporative fraction are the frst indications of positive climate feedback mechanisms, which we
show that will continue and intensify in the course of unfolding anthropogenic climate change.


(1) Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles, USA. (2) Jet Propulsion
Laboratory, California Institute of Technology, Pasadena, USA. (3) Institute of Environment and Sustainability,
University of California, Los Angeles, USA. (4) University of Arizona, Department of hydrology and atmospheric
sciences, Tucson, USA. (5) Portland State University, Department of Geography, Portland Oregon, USA. *email:

[/vc_column_text][/vc_column][/vc_row][vc_row][vc_column][vc_column_text]Read the article in PDF here: A Recent Systematic Increase in Vapor Pressure Defcit over Tropical South America



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