Location: Northwest Watershed Research CenterTitle: Numerical evaluation of a sensible heat balance method to determine rates of soil freezing and thawing
|KOJIMA, YUKI - Iowa State University|
|HEITMAN, JOSHUA - North Carolina State University|
|HORTON, ROBERT - Iowa State University|
Submitted to: Vadose Zone Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/12/2012
Publication Date: 2/28/2013
Citation: Kojima, Y., Flerchinger, G.N., Heitman, J., Horton, R. 2013. Numerical evaluation of a sensible heat balance method to determine rates of soil freezing and thawing. Vadose Zone Journal. DOI: 10.2136/vzj2012.0053..
Interpretive Summary: Ice content of frozen soils has a large influence on water movement, infiltration, and ultimately runoff and flooding, but there are no easy and accurate methods to measure soil ice content. The theoretical feasibility of using a simple energy balance calculation in conjunction with a heated probe to compute soil ice content was tested by comparing it to a complex numerical model of soil freezing and thawing. Close agreement between the two methods indicate that the new method is conceptually suitable for measuring ice formation and thawing in soils. This research may ultimately lead to a new soil sensor to measure soil ice content for better predicting the likelihood of flooding and other adverse effects associated with soil freezing.
Technical Abstract: In-situ determination of ice formation and thawing in soils is difficult despite its importance for many environmental processes. A sensible heat balance (SHB) method using a sequence of heat pulse probes has been shown to accurately measure water evaporation in subsurface soil, and it has the potential to measure soil freezing/thawing. However, determination of soil freezing/thawing may be more challenging than soil water evaporation because latent heat for fusion is smaller than for vaporization, and more unaccounted convective heat flow associated with liquid water flow may occur during freezing/thawing than during evaporation. The objective of this study is to examine the applicability of the SHB concept to soil freezing/thawing. Soil freezing/thawing events were simulated numerically with the simultaneous heat and water (SHAW) model. Ice content transitions were determined by applying the SHB concept to numerical data produced by the SHAW model. Close agreements between the SHB method and the SHAW model simulations were found for transitions of ice contents at depths below 24 mm. Ice contents in the 12-24 mm soil layer were accurately described for some surface boundary conditions. Possible reasons for inaccuracies in the SHB method may be due to changes in thermal properties and temperatures within SHB calculation time intervals, and the concurrence of evaporation or sublimation with freezing/thawing. The effect of convective heat transfer associated with liquid water flow on the SHB method was found to be negligible. The results indicate that the SHB method is conceptually suitable for estimating ice formation and thawing in soils.