TY - JOUR
T1 - Capillary, Film, and Vapor Flow in Transient Bare Soil Evaporation (2)
T2 - Experimental Identification of Hydraulic Conductivity in the Medium to Dry Moisture Range
AU - Iden, Sascha C.
AU - Diamantopoulos, Efstathios
AU - Durner, Wolfgang
PY - 2021
Y1 - 2021
N2 - Bare-soil evaporation involves coupled flow of liquid water, water vapor, and heat. As evaporation results in non-isothermal conditions in the soil, the temperature dependence of transport properties and thermal fluxes of water and vapor must be accounted for. In a companion paper, we showed that the Richards equation, that is, a single-phase flow model assuming isothermal conditions, is applicable to accurately determine soil hydraulic properties including the medium to dry range from evaporation experiments by inverse modeling. This is warranted if pressure head data across a wide moisture range, that is, from almost saturated to almost air-dry, are used in the objective function and a suitable parameterization of the hydraulic conductivity function including vapor and non-capillary flow is used. In this article, we confirm the theoretical results by examining real evaporation experiments, in which we measured the temporal dynamics of evaporation rate, soil temperature, and pressure head in laboratory soil columns. Pressure head was measured with mini-tensiometers and relative humidity sensors. The measurements were evaluated by inverse modeling with the Richards equation assuming isothermal conditions and ambient temperature in the soil. Our results for a sandy and a loamy soil show that the observed transient water and vapor dynamics in the drying soil could be accurately matched, provided the hydraulic conductivity curve considered isothermal vapor diffusion and film flow. These components dominate hydraulic conductivity in the medium to dry soil moisture range and were uniquely identified in agreement with the theoretical analysis in the companion article.
AB - Bare-soil evaporation involves coupled flow of liquid water, water vapor, and heat. As evaporation results in non-isothermal conditions in the soil, the temperature dependence of transport properties and thermal fluxes of water and vapor must be accounted for. In a companion paper, we showed that the Richards equation, that is, a single-phase flow model assuming isothermal conditions, is applicable to accurately determine soil hydraulic properties including the medium to dry range from evaporation experiments by inverse modeling. This is warranted if pressure head data across a wide moisture range, that is, from almost saturated to almost air-dry, are used in the objective function and a suitable parameterization of the hydraulic conductivity function including vapor and non-capillary flow is used. In this article, we confirm the theoretical results by examining real evaporation experiments, in which we measured the temporal dynamics of evaporation rate, soil temperature, and pressure head in laboratory soil columns. Pressure head was measured with mini-tensiometers and relative humidity sensors. The measurements were evaluated by inverse modeling with the Richards equation assuming isothermal conditions and ambient temperature in the soil. Our results for a sandy and a loamy soil show that the observed transient water and vapor dynamics in the drying soil could be accurately matched, provided the hydraulic conductivity curve considered isothermal vapor diffusion and film flow. These components dominate hydraulic conductivity in the medium to dry soil moisture range and were uniquely identified in agreement with the theoretical analysis in the companion article.
KW - Evaporation
KW - hydraulic conductivity
KW - inverse modeling
KW - soil hydraulic properties
KW - vadose zone
KW - water retention curve
U2 - 10.1029/2020WR028514
DO - 10.1029/2020WR028514
M3 - Journal article
AN - SCOPUS:85106712690
VL - 57
JO - Water Resources Research
JF - Water Resources Research
SN - 0043-1397
IS - 5
M1 - e2020WR028514
ER -