Assessing bare-soil evaporation from different water-table depths using lysimeters and a numerical model in the Ordos Basin, China
Author(s)
Ma, Zhitong
Wang, Wenke
Zhang, Zaiyong
Wang, Zhoufeng
Chen, Li
Zhao, Ming
Date issued
July 2019
In
Hydrogeology Journal
No
27
From page
2707
To page
2718
Reviewed by peer
1
Subjects
Soil evaporation Extinction depth Numerical modeling Lysimeter Arid-region
Abstract
In semiarid and arid regions, the evaporation from bare soil is highly sensitive to changes in the depth to the water table. This
study quantifies the relation between water-table depth and the groundwater contribution to evaporation in the Ordos Basin in
China. In-situ field experiments were combined with numerical simulations of heat, vapor and liquid water flow. Based on
lysimeter experiments and a calibrated numerical model, a relation between depth to groundwater and evaporation rate was
established for the lysimeter site. In addition, a sensitivity analysis considering the hydraulic conductivity and the inverse of the
air-entry pressure (vanGenuchten α) was established. For the field site, the results showed that for the water-table depths less than
52 cm below the ground, evaporation is independent of the water-table depth. For water-table depths exceeding 52 cm, an
exponential relation between depth to groundwater and evaporation is observed. No phreatic evaporation occurs for water tables
deeper than 105 cm, which is nearly two times the capillary fringe height. The sensitivity analysis showed that the extinction
depth decreased with decreasing hydraulic conductivity and increased with α. The field-specific results and the sensitivity
analysis provide valuable information to understand the dynamic processes of soil evaporation in the Ordos Basin. From a
methodological point of view, the proposed modelling approach and the integration of lysimeter data proved to be a highly
efficient combination to study evaporation dynamics in semi-arid and arid environments.
study quantifies the relation between water-table depth and the groundwater contribution to evaporation in the Ordos Basin in
China. In-situ field experiments were combined with numerical simulations of heat, vapor and liquid water flow. Based on
lysimeter experiments and a calibrated numerical model, a relation between depth to groundwater and evaporation rate was
established for the lysimeter site. In addition, a sensitivity analysis considering the hydraulic conductivity and the inverse of the
air-entry pressure (vanGenuchten α) was established. For the field site, the results showed that for the water-table depths less than
52 cm below the ground, evaporation is independent of the water-table depth. For water-table depths exceeding 52 cm, an
exponential relation between depth to groundwater and evaporation is observed. No phreatic evaporation occurs for water tables
deeper than 105 cm, which is nearly two times the capillary fringe height. The sensitivity analysis showed that the extinction
depth decreased with decreasing hydraulic conductivity and increased with α. The field-specific results and the sensitivity
analysis provide valuable information to understand the dynamic processes of soil evaporation in the Ordos Basin. From a
methodological point of view, the proposed modelling approach and the integration of lysimeter data proved to be a highly
efficient combination to study evaporation dynamics in semi-arid and arid environments.
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journal article
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