Sensible Heat Balance Method to Determine Rates of Soil Freezing and Thawing: Model Evaluation.

Soil freezing and thawing have critical effects on water and chemical movement in soil during winter and spring. Temporal in-situ measurements of ice formation and its thawing in soil have been difficult to obtain in spite of the importance. A sensible heat balance method using a sequence of heat-pulse probes (HPP) has been shown to accurately measure water evaporation/condensation in soil. This sensible heat balance method has the possibility of being applied to soil freezing/thawing and to monitoring ice content changes. To examine the applicability of the sensible heat balance method in freezing/thawing, soil freezing/thawing events were simulated numerically with the simultaneous heat and water (SHAW) model, and temporal changes in ice contents were calculated with the sensible heat balance method. Agreement for transitions of ice content between the sensible heat balance method and SHAW model simulation were shown in relatively dry soils. However, ice contents in the 0-1cm soil layer were not accurately expressed with the sensible heat balance method due to evaporation/condensation effects in the shallow soil. The sensible heat balance method slightly underestimated ice content increases when initial soil water contents were relatively large. Subsurface vapor transfer is a possible reason for the small differences. The results of this numerical study indicated that the heat balance method was suitable for estimating ice formation and thawing in subsurface soil layers.