Evaluation of Model Concepts to Describe Water Transport in Shallow Subsurface Soil and Across the Soil–Air Interface
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2018-09-17Author
Li, Zhen
Vanderborght, Jan
Smits, Kathleen M.
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**Please note that the full text is embargoed** ABSTRACT: Soil water evaporation plays a critical role in mass and energy exchanges across the land–
atmosphere interface. Although much is known about this process, there is no agreement on
the best modeling approaches to determine soil water evaporation due to the complexity of
the numerical modeling scenarios and lack of experimental data available to validate such
models. Existing studies show numerical and experimental discrepancies in the evaporation
behavior and soil water distribution in soils at various scales, driving us to revisit the key
process representation in subsurface soil. Therefore, the goal of this work is to test different
mathematical formulations used to estimate evaporation from bare soils to critically evaluate
the model formulations, assumptions and surface boundary conditions. This comparison
required the development of three numerical models at the REV scale that vary in their complexity
in characterizing water flow and evaporation, using the same modeling platform. The
performance of the models was evaluated by comparing with experimental data generated
from a soil tank/boundary layer wind tunnel experimental apparatus equipped with a sensor
network to continuously monitor water–temperature–humidity variables. A series of experiments
were performed in which the soil tank was packed with different soil types. Results
demonstrate that the approaches vary in their ability to capture different stages of evaporation
and no one approach can be deemed most appropriate for every scenario. When a proper top boundary condition and space discretization are defined, the Richards equation-based models (Richards model and Richards vapor model) can generally capture the evaporation behaviors across the entire range of soil saturations, comparing well with the experimental data. The simulation results of the non-equilibrium two-component two-phase model which considers vapor transport as an independent process generally agree well with the observations in terms of evaporation behavior and soil water dynamics. Certain differences in simulation results can be observed between equilibrium and non-equilibrium approaches. Comparisons of the
models and the boundary layer formulations highlight the need to revisit key assumptions
that influence evaporation behavior, highlighting the need to further understand water and
vapor transport processes in soil to improve model accuracy. [© The Author(s) 2018. This is a published version of an article published by Springer in Transport in Porous Media on September 17, 2018, available online: https://doi.org/10.1007/s11242-018-1144-9].