Floods are a natural hazard with widespread and far-reaching effects on public and global health, infrastructure, agriculture, and the economy. Given their global occurrence and the potential for severe and extensive damage to many facets of life, it is critical to understand the factors that influence their chances of development. One factor that has been growing in recognition is the response of plant physiology to elevated CO2, namely, reduced stomatal conductance and CO2 fertilization effects. As atmospheric CO2 concentrations increase, stomatal conductance declines, decreasing water loss through transpiration and allowing more moisture to stay on land. The CO2 fertilization effect, however, enhances plant growth, potentially increasing the number of stomata and offsetting the reduction in stomatal conductance. This plant growth can also influence leaf area, which impacts canopy precipitation, interception, and evaporation. Using Earth system model simulations that isolate the plant and radiative effects of rising CO2 (C4MIP), we investigate these plant physiological effects and their influence on water resources and flood potential. Globally, we find that some regions increase while other regions decrease in flood risk, with areas of interest including the northern high-latitudes, the Southeastern United States, Southern and Eastern Asia, and much of the tropics.