Forest response to rising CO2 drives zonally asymmetric rainfall change over tropical land


Understanding how anthropogenic CO2 emissions will influence future precipitation is critical for sustainably managing ecosystems, particularly for drought-sensitive tropical forests. Although tropical precipitation change remains uncertain, nearly all models from the Coupled Model Intercomparison Project Phase 5 predict a strengthening zonal precipitation asymmetry by 2100, with relative increases over Asian and African tropical forests and decreases over South American forests. Here we show that the plant physiological response to increasing CO2 is a primary mechanism responsible for this pattern. Applying a simulation design in the Community Earth System Model in which CO2 increases are isolated over individual continents, we demonstrate that different circulation, moisture and stability changes arise over each continent due to declines in stomatal conductance and transpiration. The sum of local atmospheric responses over individual continents explains the pan-tropical precipitation asymmetry. Our analysis suggests that South American forests may be more vulnerable to rising CO2 than Asian or African forests.

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Fig. 1: Multi-model mean annual mean precipitation change and tropical precipitation asymmetry index.
Fig. 2: Annual mean precipitation change from the CESM.
Fig. 3: Seasonal and interannual precipitation variability.
Fig. 4: Changes in evapotranspiration and specific humidity.
Fig. 5: Annual mean moisture budget (precipitation, evapotranspiration and moisture convergence) and normalized gross moist stability changes.


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G.J.K., Y.C. and J.T.R. acknowledge support from the Gordon and Betty Moore Foundation (GBMF3269). C.D.K., F.M.H., M.S.P. and J.T.R. acknowledge support from the US Department of Energy (DOE) Office of Science Biological and Environmental Research programmes. The DOE support includes funding from the Regional and Global Climate Modeling programme to the Reducing Uncertainties in Biogeochemical Interactions through Synthesis and Computation (RUBISCO) Scientific Focus Area, from the Terrestrial Ecosystem Sciences programme to the Next Generation Ecosystem Experiments — Tropics, and from the Early Career programme (DE-SC0012152). K.L. acknowledges support from the National Center for Atmospheric Research (NCAR), which is sponsored by the US National Science Foundation (NSF). A.L.S.S. acknowledges support from the NSF (AGS-1321745 and AGS-1553715). CESM development is led by NCAR and supported by the NSF and DOE. CESM simulations were run at the NSF NCAR Computational and Information Systems Laboratory on Yellowstone (P36271028).

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All authors contributed to designing the experiment, interpreting the results and editing the manuscript. G.J.K. performed the simulations, carried out the analysis and drafted the manuscript. M.S.P. conducted the moist stability analysis.

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Correspondence to Gabriel J. Kooperman.

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Supplementary Figures 1–7, Supplementary Tables 1–5 and Supplementary Methods

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Kooperman, G.J., Chen, Y., Hoffman, F.M. et al. Forest response to rising CO2 drives zonally asymmetric rainfall change over tropical land. Nature Clim Change 8, 434–440 (2018).

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