Soil thermal conductivity and its influencing factors at the Tanggula permafrost region on the Qinghai–Tibet Plateau.

Highlights • Lower λ in frozen state was accounted for small initial freeze moisture content. • Soil thermal conductivity λ decreased with increase in freeze-thaw cycle times. • The critical soil moisture content was about 0.195 m3 m−3. • The critical degree of saturation was 0.37. • The contribution of soil moisture content to λ was different at different state. Abstract Soil thermal conductivity (λ) is one of the essential parameters relating to heat exchange, and it also plays a key role in verifying soil thermal hydrodynamics in permafrost regions. In this paper, the characteristic of in situ λ was analyzed based on data measured from June 2004 to December 2008 at Tanggula district on the Qinghai–Tibet Plateau. The result showed that diurnal λ strongly influenced by variation of soil moisture content. The daily λ exhibited distinct seasonal variation; on average, the largest value of λ occurred in summer, followed by the autumn and spring season, while the smallest value occurred in winter. As a whole, λ values in the unfrozen state were larger than those in the frozen state. Unsaturated soil and the huge difference in soil moisture content between the unfrozen state and initial freeze resulted in the lower λ in the frozen state. For the study area, the critical value of local soil saturation degree was about 0.37, the corresponding critical soil moisture content was about 0.195 m3 m−3. And soil moisture content was the main factor controlling in situ λ. Finally, an empirically-derived model was proposed for predicting daily λ , and which showed good performance in the study area. [ABSTRACT FROM AUTHOR]