Pore structure and falling rate stage of evaporation in homogeneous sandy soil profiles

Abstract

Recently, climate change has been causing severe droughts and water scarcity in drylands. A proper understanding of the soil surface-atmosphere boundary fluxes is essential to combatting such environmental problems. In those regions, evaporation is considered to be the dominant flux. It is divided into three stages that follow different mechanisms and are highly dependent on the soil properties. Most of the existing studies focus on the evaporation process from a macroscale perspective and estimate the evaporation rate based on the atmospheric conditions, while only a few of them consider the soil properties. This paper studied the influence of the soil pore structure on the actual evaporation and formation of the unsaturated layer. Homogeneous drying sandy soil column tests were conducted under a unified low atmospheric demand. The pore structure was investigated by varying the texture and relative density. The significance of Stage 2 in the evaporation process was asserted. Additionally, it was affirmed that vapor diffusion is dominant during Stage 2, where the actual evaporation reduction rate depends on the receding rate of the vaporization plane. Finally, a comprehensive, robust, and easily determined index, that correlates well with the duration and evaporated water during Stage 1 and Stage 2, was proposed. The Pore Size Distribution Index (IPSD) was found to reflect the variations in the pore structure and to consider the capillary and diffusion flow mechanisms. It serves as a fundamental step towards evaluating the actual evaporation and drying front depth during the evaporation process.