Evaluating the effect of the surface soil layer on the near-surface state variables during evaporation
Abstract
The soil property profile plays a significant role in determining the hydrological state variables (e.g. soil moisture, soil temperature, evaporation flux) in hydrological modeling. Field soil profiles are commonly heterogeneous rather than uniform in vertical direction, typically in a layered formation with different hydraulic properties in individual layers. The inaccurate description of the soil property profiles can lead to deviation between simulation results and the observations. We study how the layered soil profile (surface soil and underlying soil) affects the near surface information that can be observed by remote sensing tools to better characterize both the soil profile system and the soil-air interactions. In this study, the bench-scale evaporation experiments were performed in the testing system consisting of a tank packed with varying layered sand configurations, a wind tunnel capable of simulating diurnal temperature environment and a sensor network which can measure variables in both the tank and in the free-flow. A model capable of simulating the coupled moisture-heat transport in layered soil was numerically solved and validated by comparing with the generated experimental data set. The measured soil evaporation behavior shows high correlations with the dynamics of the temperature and relative humidity at the soil surface in varying layered configurations and free-flow conditions. The evaporation dynamics, phase distribution and soil retention behavior can be significantly affected by the soil layering, the extent of the effect depends on the layering sequence, thickness and the property of the layers. When the surface soil is a coarse layer in a C/F (coarse over fine) system, the surface coarse layer dries quickly and behaves as the capillary barrier, reducing the cumulative evaporation. However, the stage II evaporation of the C/F system can be higher than a homogeneous coarse system if the coarse layer thickness is smaller than its characteristic length, resulting from its smaller diffusive path length compared with a constantly downward-moving evaporation front of a homogeneous soil profile. The results indicate the importance of characterizing the soil property profiles in accurately estimating the hydrologic state variables of the near-surface soil.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.H53N1993L
- Keywords:
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- 1843 Land/atmosphere interactions;
- HYDROLOGY;
- 1847 Modeling;
- HYDROLOGY;
- 1865 Soils;
- HYDROLOGY;
- 1875 Vadose zone;
- HYDROLOGY