Effects of root water uptake formulation on simulated water and energy budgets at local and basin scales

Roots connect water stored beneath the Earth’s surface to water in the atmosphere. The fully integrated hydrologic model ParFlow coupled to the Common Land Model is used to investigate the influence of the root uptake formulation on simulated water and energy fluxes and budgets at local and watershed scales. The effects of four functional representations of vegetation water stress and plant wilting behavior are evaluated in the semi-arid Little Washita watershed of the Southern Great Plains, USA. Monthly mean latent and sensible heat fluxes differ by more than 25 W m^-2 over much of the study area during hot, dry summer conditions. This difference indicates that the root uptake formulation has a substantial impact on simulated land energy fluxes and land–atmosphere interactions. Differences in annual evapotranspiration and stream discharge over the watershed exceed 14.5 and 55.5 % between simulations, respectively, demonstrating significant impacts on simulated water budgets. Notably, the analysis reveals that spatial variability in the sensitivity of local-scale water and energy fluxes to root uptake formulation is primarily driven by feedbacks between water table dynamics, soil moisture, and land energy fluxes. These results have important implications for model development, calibration, and validation.