GC095-09
Soil moisture-atmosphere feedbacks mitigate projected surface water availability declines in drylands

Monday, 14 December 2020: 21:02
Virtual
Sha Zhou, Columbia University of New York, Lamont-Doherty Earth Observatory, Palisades, NY, United States, Park Williams, Columbia University, Lamont -Doherty Earth Observatory, Palisades, NY, United States, Benjamin R Lintner, Rutgers, New Brunswick, NJ, United States, Alexis M Berg, Rutgers University New Brunswick, New Brunswick, NJ, United States, Yao Zhang, Lawrence Berkeley National Laboratory, Climate and Ecosystem Sciences Division, Berkeley, CA, United States, Trevor F Keenan, Lawrence Berkeley National Laboratory, Berkeley, CA, United States, Benjamin Cook, NASA-GISS, New York, NY, United States, Stefan Hagemann, Heimholtz-Zentrum Geesthacht, Geesthacht, Germany, Sonia I Seneviratne, Institute for Atmospheric and Climate Science, ETH Zürich, Zürich, Switzerland and Pierre Gentine, Columbia University, Earth and Environmental Engineering, New York, NY, United States
Recorded Presentation
Abstract:
Global warming is expected to change surface water availability (precipitation minus evapotranspiration, P-E) and hence freshwater resources. However, the influence of land-atmosphere feedbacks on future P-E changes and the underlying mechanisms remain unclear. Here we demonstrate that soil moisture (SM) strongly impacts future P-E changes, especially in drylands, through regulating evapotranspiration and atmospheric moisture inflow. To do so, we use transient simulations from general circulation models, both with and without long-term SM changes, along with empirical statistical models of SM-atmosphere feedbacks. We find a consistent negative SM feedback on P-E, which may offset up to ~60% of the decline in dryland P-E that is otherwise expected to occur. The negative feedback is not caused by atmospheric thermodynamic responses, i.e., temperature and humidity changes, to declining SM, but rather by SM-related regulation of atmospheric circulation and vertical ascent that enhance moisture transport towards drylands. This SM effect is a large source of uncertainty in projected dryland P-E changes, underscoring the need to better constrain future SM changes and improve representation of SM-atmosphere processes in models.
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