How soil moisture influences climate through interactions in the coupled water, energy, and carbon cycles is a key challenge that is not well understood. A team of scientists, led by Department of Energy researchers at Pacific Northwest National Laboratory, studied how uncertainty caused by structural differences between two hydrologic parameterizations may influence carbon cycle simulations. Using the Community Land Model version 4 with two widely-adopted runoff generation parameterizations, from the TOPMODEL and Variable Infiltration Capacity (VIC) model, the team found that the global water balance is sensitive to the runoff generation parameterizations, which caused a relative difference of 36% and 34% in global mean total runoff and soil moisture and substantial differences in their spatial distribution and seasonal variability. Consequently, the simulated global mean gross primary production differs by 20.4% as differences in soil moisture simulated between the two models directly influence leaf photosynthesis through soil moisture availability, and indirectly alter vegetation phenology through the impacts of soil moisture on soil temperature. Our study highlights the significant interactions among the water, energy, and carbon cycles and the need for reducing uncertainty in the hydrologic parameterization of land surface models to better constrain carbon cycle modeling.