Effects of Root Water Uptake Parameterizations on Land-Atmosphere Exchanges at Local and Basin Scales

Transpiration is the dominant component of latent heat flux over most vegetated areas and thus plays an important role in the land-atmosphere water and energy balance, atmospheric boundary layer development, and weather and climate processes. The transpiration response to changes in soil moisture availability—and thus the magnitude of soil moisture feedbacks—depends on the distribution and efficiency of water uptake by plant roots over the soil column. While a variety of root uptake and water stress parameterizations are used in land surface models, the sensitivity of simulated water and energy budgets and land-atmosphere feedbacks to the choice of parameterization is not well understood. Here we use the fully-integrated hydrologic model ParFlow to investigate the influence of varying root uptake parameterizations on water and energy budgets at local and watershed scales. As expected, the choice of parameterization is shown to strongly influence local-scale (1km) land-atmosphere fluxes under moisture-limited conditions, as well as the magnitude and spatial distribution of fluxes at the watershed scale. In addition, root uptake parameterization is shown to significantly impact basin-scale groundwater storage and stream discharge throughout the water year. Results highlight the importance of ecohydrology in understanding and modeling terrestrial hydrology and land-atmosphere interactions.