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.