Parameterization model of soil thermal conductivity and its application in the permafrost region of the Qinghai-Tibet Plateau

Soil thermal conductivity (STC), which describes the ability of soil to transfer heat, is critical to understanding the thermal regime. Simulations of the heat of the permafrost regions on the Qinghai-Tibet Plateau (QTP) are currently inaccurate. This is partly because the current STC models used in the land surface models are not adequate to accurately reflect the characteristics of the ice-water phase change. Here, the new STC model was developed by dividing three different stages. Our analyses revealed that the soil moisture ( θ w ) undergoes a rapid phase change in the − 2.5 ~ 0 ℃, where minor temperature changes could cause larger θ w changes. When the temperature is below − 2.5 ℃, the θ w mostly remains stable. Considering the influence of various factors in different temperature ranges, an improved STC model was proposed by piecewise fitting at 0 ℃ and − 2.5 ℃ for the depths of 10–50 cm. Independent test results showed that the new model significantly improved simulation accuracy of STC in permafrost regions and was better able to reflect it changing characteristics, especially in the 50 cm depth. Lastly, the daily STC product in the permafrost region of the QTP was estimated with the new model. The average STC during 1982 to 2020 was about 0.495 Wm −1 K −1 , showing a spatial pattern of low in the northwest and high in the southeast. In addition, the STC showed a tiny increasing trend at a rate of 0.008 Wm −1 K −1 /10a. Spatially, the regions with the highest rates of increase were concentrated in the eastern, southeastern, and south-western regions, which comprise mostly unstable and extremely unstable permafrost. This study deepened our understanding of the STC during the freeze–thaw cycle and provides data products for further studies on the soil thermal state in permafrost regions.