The Relative Importance of Water Vapor Flux from the Perspective of Heat and Mass Movement

Water movement is normally modelled in the soil to quantify spatial and temporal soil moisture distribution. This is important given that soil moisture indicates the amount of water available to plant consumption and also imply the necessity of water sourcing, storage and distribution system to maintain agricultural activities. Modelling soil moisture content in soil is often limited to water mass flux in the mass balance equation. A limited account is given to water vapor contribution to mass flux. Adding to the complexity, the liquid water, and water vapor mass fluxes are influenced by soil heat flux. In this study, five mechanisms driving overall mass fluxes, and seven mechanisms driving overall heat fluxes were quantified based on the published experimental data from Heitman and his co-workers. The study was carried out on silt loam and sandy soil in a drier soil condition at 0.1 and 0.08 m3∙m-3, respectively. The relative comparison between the mechanisms and the soil types clearly shows that water vapor mass flux dominates in the overall mass fluxes, while water vapor heat flux repeatedly ranked second the most important among the seven mechanisms quantified on overall heat fluxes in which there were only three water vapor-heat flux mechanisms exist, the rest four mechanisms are from liquid water-heat flux. Clearly, water vapor flux is a necessary inclusion in heat and mass movement estimation.