A comparative investigation on the in-situ thermal conductivity between Arctic tundra and alpine meadow in the hinterland of the Qinghai-Tibet Plateau

The permafrost types in the Arctic and Qinghai-Tibet Plateau (QTP) are different, resulting in significant differences in their thermal characteristics. Soil thermal conductivity (STC) is a key physical parameter in land surface processes that controls the storage and conduction of heat in soil, and it is of great significance for simulating the thermal state of frozen soil. Here,a comparative study on STC of the active layer surface soil between the Arctic tundra and alpine meadow in hinterland of the QTP was conducted. Results show that the STC of the Arctic tundra and the alpine meadow in  hinterland of the QTP exhibit an opposite patterns. During study period,  monthly average STC of the Arctic tundra varied significantly with seasons, reaching a maximum of 1.989 Wm^-1K^-1 in cold season and a minimum of 0.761 Wm^-1K^-1 in warmer season, with an annual average of 1.541 Wm^-1K^-1. For Arctic tundra, STC in frozen state was 1.787 Wm^-1K^-1, while in the unfrozen state, it was 0.802 Wm^-1K^-1. In contrast, the monthly average STC for alpine meadow in the hinterland of the QTP showed opposite pattern, with the minimum value of 0.933 Wm^-1K^-1 occurred in January and the maximum value of 1.375 Wm^-1K^-1 occurred in September, and an annual average of 1.151 Wm^-1K^-1. In frozen state STC was 0.962 Wm^-1K^-1 while in unfrozen state such value was 1.341 Wm^-1K^-1. Field observation experiments in both regions found that STC is strongly dependent on soil moisture content. The initial frozen water content of the Bylot tundra in the Arctic was approximately 0.531 m³m^-3 (0.495~ 0.565 m³m^-3), while that of the Tanggula alpine meadow in the hinterland of the QTP was 0.142 m³m^-3 (0.167~0.115 m³m^-3), only 26.7% of the Arctic tundra. This significant difference in initial frozen water content is the main reason for the difference in STC between the two regions. Additionally, rapid changes in unfrozen water content have a great impact on STC during freezing process. For the Arctic tundra observation site, the STC increased by 0.273 Wm^-1K^-1 (0.247~0.300 Wm^-1K^-1) for every 0.100 m³m^-3 decrease in unfrozen water content. While for the alpine meadow of the QTP, the STC decreased by 0.163 Wm^-1K^-1 for every 0.100 m³m^-3 decrease in unfrozen water content. On average, in the Arctic tundra, the STC of the active layer surface decreases with increasing soil liquid water content, while in the alpine meadow of the QTP, it increases with increasing soil liquid water content. In frozen state for Arctic tundra, the contribution of soil ice content and unfrozen water to thermal conductivity is 75.6% and 5.2%, respectively. It can be seen that STC of the Arctic tundra active layer is mainly controlled by the ice content. As for the QTP meadow, such values were 25.9% and 41.8%, respectively. That means unfrozen water content is the dominant factor for STC changes in the QTP meadow. Furthermore, the Kerstern number scheme was optimized based on the STC data obtained from in-situ observations and KD₂ Pro dehumidification experiments of soil samples under different soil moisture conditions.