The effect of plant physiological responses to rising CO2 on global streamflow


River flow statistics are expected to change as a result of increasing atmospheric CO2 but uncertainty in Earth system model projections is high. While this is partly driven by changing precipitation, with well-known Earth system model uncertainties, here we show that the influence of plant stomatal conductance feedbacks can cause equally large changes in regional flood extremes and even act as the main control on future low latitude streamflow. Over most tropical land masses, modern climate predictions suggest that plant physiological effects will boost streamflow, overwhelming opposing effects of soil drying driven by the effects of CO2 on atmospheric radiation, warming and rainfall redistribution. The relatively unknown uncertainties in representing eco-physiological processes must therefore be better constrained in land-surface models. To this end, we identify a distinct plant physiological fingerprint on annual peak, low and mean discharge throughout the tropics and identify river basins where physiological responses dominate radiative responses to rising CO2 in modern climate projections.

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Fig. 1: Frequency of the pre-industrial 100-yr flood under elevated CO2 and its drivers.
Fig. 2: Changes in seasonal streamflow.
Fig. 3: Changes in environmental conditions.
Fig. 4: Basin-level streamflow percentage changes.
Fig. 5: Average annual streamflow cycles at river outlets in PHYS-dominated basins.

Data availability

The relevant datasets generated during this analysis are available at The full CESM output record is archived and available upon request. Data used to create Fig. 1b were received via personal correspondence with Y. Hirabayashi and requests should be directed to her ( Similarly, CMIP5 multimodel mean streamflow data used for comparison between FULL and K14 were received via personal communication with the lead author and should be requested from S. Koirala ( Full CESM output is archived at the National Center for Atmospheric Research. Global Runoff Data Base observations in Fig. 5 are freely available from GRDC but cannot be redistributed by the author; requests should be sent directly to GRDC.

Code availability

All scripts that replicate the results of this study are accessible at Data associated with these scripts are included in the repository, with a few exceptions. Relevant CESM and CaMa output are not included due to their size but are available at Data obtained from Y. Hirabayashi, S. Koirala and from the GRDC are not included and should be requested from the sources independently. The CaMa model itself can be obtained by emailing the developer, D. Yamazaki (, while CESM is publicly available through a Subversion code repository—see for more details.


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M.D.F. and M.S.P. acknowledge primary support from the US Department of Energy Early Career Program (grant no. DE-SC0012152) and additional support from the National Science Foundation (grant no. AGS-1734164). G.J.K. and J.T.R. acknowledge support from the Gordon and Betty Moore Foundation (grant no. GBMF3269) and the RUBISCO science focus area supported by the Regional & Global Climate Modeling Program in the Climate and Environmental Sciences Division of the US Department of Energy, Office of Science. G.J.K. also acknowledges support from the US Department of Energy, Regional and Global Model Analysis Program (grant no. DE-SC0019459). CESM simulations were run and archived at the National Center for Atmospheric Research, Computational and Information Systems Laboratory on Yellowstone (P36271028). Analysis was run in part on XSEDE supported systems Stampede2 (TG-ATM160016) and Comet (TG-ASC150024).

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All authors contributed to the design of the experiment, interpretation of results and manuscript editing. G.J.K. performed the CESM simulations and M.D.F. performed the CaMa downscaling, carried out the analysis and drafted the initial manuscript with advice from M.S.P.

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Correspondence to Megan D. Fowler.

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Peer review information Nature Climate Change thanks Robert Dickinson, Christopher Schwalm and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary Figs. 1–9, Tables 1–7, note and references.

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Fowler, M.D., Kooperman, G.J., Randerson, J.T. et al. The effect of plant physiological responses to rising CO2 on global streamflow. Nat. Clim. Chang. 9, 873–879 (2019).

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