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How Airflow Affects Soil Water Dynamics
Abstract and Figures
The concept of enhanced vapor transfer in unsaturated soils has been questioned for its reliance on soil temperature gradient, which leads to consideration of other mechanisms of vapor transfer, e.g. advective vapor transfer due to soil air pressure gradient. Although the advective flux is an important portion of evaporation, there is a lack of knowledge in its effect on evaporation. In order to assess the dependence of evaporation on the soil air pressure gradient, the vertical one-dimensional two-phase heat and mass flow model developed in Chap. 4 is used to investigate the advective effect in both low- and high-permeability soils. The advective effect is reflected by underestimating evaporation when the airflow is neglected and is more evident in the low-permeability soil. Neglecting airflow causes the underestimation error of 53.3 % on the day right after rainfall event in the low-permeability soil (7.9 × 10−4 cm s−1), and 33.3 % in the high-permeability soil (2 × 10−3 cm s−1). The comparisons of driving forces and conductivities show that the isothermal liquid flux, driven by the soil matric potential gradient, is the main reason for the underestimation error.
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