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

Soil thermal conductivity (lambda) 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 lambda 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 lambda strongly influenced by variation of soil moisture content. The daily lambda exhibited distinct seasonal variation; on average, the largest value of lambda occurred in summer, followed by the autumn and spring season, while the smallest value occurred in winter. As a whole, lambda 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 lambda 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 m(3) m(-3). And soil moisture content was the main factor controlling in situ lambda. Finally, an empirically-derived model was proposed for predicting daily lambda, and which showed good performance in the study area.