New insights into the correlation between soil thermal conductivity and water retention in unsaturated soils
Yongwei Fu, Behzad Ghanbarian, Robert Horton, Joshua L. Heitman
Abstract
Abstract The heat transfer and water retention in soils, governed by soil thermal conductivity (λ) and soil water retention curve (SWRC), are coupled. Soil water content (θ) significantly affects λ. Several models have been developed to describe λ(θ) relationships for unsaturated soils. Ghanbarian and Daigle presented a percolation‐based effective‐medium approximation (P‐EMA) for λ(θ) with two parameters: scaling exponent ( t s ) and critical water content (θ c ). In this study, we explored the new insights into the correlation between soil thermal conductivity and water retention using the P‐EMA and van Genuchten models. The θ c was strongly correlated to selected soil hydraulic and physical properties, such as water contents at wilting point (θ pwp ), inflection point (θ i ), and hydraulic continuity (θ hc ) determined from measured SWRCs for a 23‐soil calibration dataset. The established relationships were then evaluated on a seven‐soil validation dataset to estimate θ c . Results confirmed their robustness with root mean square error ranging from 0.011 to 0.015 cm 3 cm −3 , MAE ranging from 0.008 to 0.013 cm 3 cm −3 , and R 2 of 0.98. Further discussion investigated the underlying mechanism for the correlation between θ c with θ hc which dominate both heat transfer and water flow. More importantly, this study revealed the possibility to further investigate the general relationship between λ(θ) and SWRC data in the future.