Preprints
https://doi.org/10.5194/hess-2021-14
https://doi.org/10.5194/hess-2021-14

  27 Jan 2021

27 Jan 2021

Review status: this preprint is currently under review for the journal HESS.

From hydraulic root architecture models to macroscopic representations of root hydraulics in soil water flow and land surface models

Jan Vanderborght1, Valentin Couvreur2, Felicien Meunier3,4, Andrea Schnepf1, Harry Vereecken1, Martin Bouda2,5, and Mathieu Javaux1,2 Jan Vanderborght et al.
  • 1Forschungszentrum Jülich GmbH, IBG-3 (Agrosphäre), Wilhelm-Johnen-Str., 52428 Jülich, Germany
  • 2University of Louvain, Earth and Life Institute, 1348 Louvain-la-Neuve, Belgium
  • 3CAVElab - Computational and Applied Vegetation Ecology, Department of Environment, Ghent University, Ghent, Belgium
  • 4Department of Earth and Environment, Boston University, Boston, USA
  • 5Institute of Botany of the Czech Academy of Sciences, Pruhonice, Czechia

Abstract. Root water uptake is an important process in the terrestrial water cycle. How this process depends on soil water content, root distributions, and root properties is a soil-root hydraulic problem. We compare different approaches to implement root hydraulics in macroscopic soil water flow and land surface models. By upscaling a three dimensional hydraulic root architecture model, we derived an exact macroscopic root hydraulic model. The macroscopic model uses three characteristics: the root system conductance, Krs, the standard uptake fraction, SUF, that represents the uptake from a soil profile with a uniform hydraulic head, and a compensatory matrix that describes the redistribution of water uptake in a non-uniform hydraulic head profile. Two characteristics, Krs and SUF, are sufficient to describe the total uptake as a function of the collar and soil water potential; and water uptake redistribution does not depend on the total uptake or collar water potential. We compared the exact model with two hydraulic root models that make a-priori simplifications of the hydraulic root architecture: the parallel and big root model. The parallel root model uses only two characteristics, Krs and SUF, that can be calculated directly following a bottom up approach from the 3D hydraulic root architecture. The big root model uses more parameters than the parallel root model but these parameters cannot be obtained straightforwardly with a bottom up approach. The big root model was parameterized using a top down approach, i.e. directly from root segment hydraulic properties assuming a-priori a single big root architecture. This simplification of the hydraulic root architecture led to less accurate descriptions of root water uptake than by the parallel root model. To compute root water uptake in macroscopic soil water flow and land surface models, we recommend the use of the parallel root model with Krs and SUF computed in a bottom up approach from a known 3D root hydraulic architecture.

Jan Vanderborght et al.

Status: open (until 25 Mar 2021)

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Jan Vanderborght et al.

Jan Vanderborght et al.

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Short summary
Root water uptake is an important process in the terrestrial water cycle. How this process depends on soil water content, root distributions, and root properties is a soil-root hydraulic problem. We compare different approaches to implement root hydraulics in macroscopic soil water flow and land surface models.