The Role of Leaf Area Changes Within Plant CO2 Physiological Impacts on the Global Hydrological Cycle

Abstract Rising atmospheric CO2 concentrations enhance greenhouse warming and drive changes to plant physiology, leading to innumerable climate impacts. This study explores the impacts of plant responses on hydrological cycling at 2x preindustrial CO2 concentrations by analyzing simulations that isolate plant physiological effects using the Community Earth System Model versions 1 and 2. We find that leaf area growth increases canopy evaporation, which offsets transpiration declines, and dampens changes in global mean evapotranspiration, precipitation, and runoff in a CESM2 experiment with dynamic leaf area. These leaf area impacts are also evident in the differences between CESM1 and CESM2, with CESM2 better capturing observed leaf area magnitudes but potentially overestimating leaf area‐CO2 sensitivity, highlighting the importance of plant CO2 physiology on hydrological cycle changes and the need to improve its representation in climate models.