Ground surface temperature and the detection of permafrost in the rugged topography on NE Qinghai-Tibet Plateau

The thermal regime of permafrost in the rugged topography on parts of the Qinghai-Tibet Plateau (QTP) remains ambiguous, due to general inaccessibility and inconvenient investigations with geophysical prospecting. While the relatively easy implementations of monitoring ground surface temperature (GST) may facilitate the investigations of permafrost thermal state. Here, surface freezing and thawing and the relationship between GST and permafrost temperature are investigated in the Bayan Har Mountains, NE QTP on the basis of 22 monitoring sites. Results demonstrate that, unlike the air temperature (Ta) mainly controlled by elevation, the GST is complicately influenced by elevation and the surface characteristics, such as vegetation, local soil textures, as well as the exposure to solar radiation. Mean annual GST (MAGST) ranges from 1.1 °C to −3.1 °C and is averaged at −0.8 °C. MAGST generally decreases at a lapse rate of 1.1 °C/100 m in relation to elevation. Surface freezing and thawing processes depend on topography and local surface characteristics. The onset of unstable thawing, stable thawing, unstable freezing, and stable freezing are averaged at 6 April 2015, 15 May 2015, 14 October 2015, and 21 October 2015. Based on the relationship between MAGST and the ground temperature at the depth of zero annual amplitude, GST likely serves as a reliable indicator of the thermal state of permafrost. For the 22 sites, it is estimated that the lowest TZAA of permafrost is −3.4 °C and the thickest permafrost is 106.2 m. However, detailed investigations of subsurface characteristics are indispensable for the accurate inference of permafrost.