Permafrost degradation related to global warming has been widespread in the Tibetan Plateau (TP), manifesting prominently as variations in the soil thermal regime, an essential characteristic of permafrost. Altered soil thermal conditions can influence the energy and water balance between the atmosphere and land, leading to the release of stored carbon dioxide and methane. In this study, reanalysis and observed soil temperature data were combined to analyse the long-term changes in the thermal regime of the uppermost soil layer at six sites in the central TP. MERRA2 and ERA5-Land had the highest quality in matching the observed data at each site. The mean annual soil temperature ranged from -0.11 degrees C to 4.75 degrees C (averaging 1.73 degrees C) and warms at 0.059 degrees C a(-1). The mean annual first dates of freezing and thawing and the mean duration of freezing were 123.23 +/- 10.85 d, 285.67 +/- 10.34 d, and 161.44 +/- 20.54 d, respectively, indicating lagged, advanced, and shortened trends with 0.54 +/- 0.49 d a(-1), 0.50 +/- 1.06 d a(-1), and 1.05 +/- 1.16 d a(-1), respectively. The mean annual freezing and thawing N-factors were 0.53 +/- 0.13 and 2.43 +/- 2.09, respectively. The maximum and minimum monthly average soil temperatures were 11.81 +/- 2.17 degrees C in July and-9.54 +/- 3.24 degrees C in January, respectively. Partial correlation analysis was used to quantify the influences of factors (including surface air temperature, snow depth, rainfall, normalised difference vegetation index [NDVI], shortwave radiation, and soil moisture) on soil temperature implicated surface air temperature as the most significant influencing factor in the increased soil temperature. Rainfall and NDVI were implicated as being likely to suppress the soil temperature warming. This study provides detailed information about the thermal regime of the uppermost soil in the central TP and facilitates validation of the land surface model.

Permafrost degradation related to global warming has been widespread in the Tibetan Plateau (TP), manifesting prominently as variations in the soil thermal regime, an essential characteristic of permafrost. Altered soil thermal conditions can influence the energy and water balance between the atmosphere and land, leading to the release of stored carbon dioxide and methane. In this study, reanalysis and observed soil temperature data were combined to analyse the long-term changes in the thermal regime of the uppermost soil layer at six sites in the central TP. MERRA2 and ERA5-Land had the highest quality in matching the observed data at each site. The mean annual soil temperature ranged from -0.11 degrees C to 4.75 degrees C (averaging 1.73 degrees C) and warms at 0.059 degrees C a(-1). The mean annual first dates of freezing and thawing and the mean duration of freezing were 123.23 +/- 10.85 d, 285.67 +/- 10.34 d, and 161.44 +/- 20.54 d, respectively, indicating lagged, advanced, and shortened trends with 0.54 +/- 0.49 d a(-1), 0.50 +/- 1.06 d a(-1), and 1.05 +/- 1.16 d a(-1), respectively. The mean annual freezing and thawing N-factors were 0.53 +/- 0.13 and 2.43 +/- 2.09, respectively. The maximum and minimum monthly average soil temperatures were 11.81 +/- 2.17 degrees C in July and-9.54 +/- 3.24 degrees C in January, respectively. Partial correlation analysis was used to quantify the influences of factors (including surface air temperature, snow depth, rainfall, normalised difference vegetation index [NDVI], shortwave radiation, and soil moisture) on soil temperature implicated surface air temperature as the most significant influencing factor in the increased soil temperature. Rainfall and NDVI were implicated as being likely to suppress the soil temperature warming. This study provides detailed information about the thermal regime of the uppermost soil in the central TP and facilitates validation of the land surface model.

Xing'anling-Baikal permafrost is located in the southern edge of the Northern Hemisphere permafrost, which is one of the most important regions of permafrost changes. Based on the monthly meteorological data and circumpolar active layer monitoring data in the last few decades, we analyzed the changes in the depth of seasonal freezing (DSF) and the thermal regime of Xing'anling-Baikal permafrost in China, and compared the state with that of the permafrost in Mongolia at the same latitude (LAT). The Xing'anling-Baikal permafrost in China was not connected in the section. The DSF changed between 0.78 and 3.25m. In the study area, DSF was the thickest in Tulihe and reduced to around. The change rate reached -16.0-4.9cm/a and decreased in most areas. The ground temperature raised at a rate of 0-0.41 degrees C/a, whereas that of other few areas decreased with a rate of -0.35 degrees C/a. Freezing duration spanned 141-176days. The changes were related to air temperature, altitude, LAT, and precipitation in the local area. Compared with the state of permafrost in Mongolia at the same LAT, the permafrost in China exhibited a faster rate of degradation. The permafrost in the Xing'anling area significantly responded to climate change. The results will aid in understanding the temporal and spatial variation in local permafrost and provide relevant verification for regional permafrost.

Beiluhe basin is underlain by warm and ice-rich permafrost, and covered by vegetation and soils characteristic of the Qinghai-Tibet Plateau. A field monitoring network was established to investigate permafrost conditions and to assess potential impacts of local factors and climate change. This paper describes the spatial variations in permafrost conditions from instrumented boreholes, controlling environmental factors, and recent thermal evolution of permafrost in the basin. The study area was divided into 10 ecotypes using satellite imagery based classification. The field investigations and cluster analysis of ground temperatures indicated that permafrost underlies most of the ground in swamp meadow, undisturbed alpine meadow, degrading alpine meadow, and desert alpine grassland, but is absent in other cover types. Permafrost-ecotope relations examined over a 2-year (2014-2016) period indicated that: (i) ground surface temperatures varied largely among ecotopes; (ii) annual mean ground temperatures ranged from 1.5 to 0 degrees C in permafrost, indicating sensitive permafrost conditions; (iii) active-layer thicknesses ranged from 1.4 m to 3.4 m; (iv) ground ice content at the top of permafrost is high, but the active-layer soil is relatively dry. Long-term climate warming has driven thermal changes to permafrost, but ground surface characteristics and soil moisture content strongly influence the ground thermal state. These factors control local-scale spatial variations in permafrost conditions. The warm permafrost in the basin is commonly in thermal disequilibrium, and is sensitive to future climate change. Active-layer thicknesses have increased by at least 42 cm and the mean annual ground temperatures have increased by up to 0.2 degrees C in the past 10 years over the basin. A permafrost distribution map was produced based on ecotypes, suggesting that permafrost underlies 64% of the study region.