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Relict permafrost presents an ideal opportunity to understand the impacts of climatic warming on the ground thermal regime since it is characterized by a mean annual ground temperature close to 0 ∘ C and relatively thin permafrost. The long-term and continuous observations of permafrost thermal state and climate background are of great importance to reveal the links between the energy balance on hourly to annual timescales, to evaluate the variations in permafrost thermal state over multiannual periods and to validate the remote sensing dataset. We present 11 years of meteorological and soil data from the Mahan Mountain relict permafrost site of northeastern Qinghai–Tibet Plateau. The meteorological data comprise air and land surface temperature, relative humidity, wind speed and direction, shortwave and longwave downwards and upwards radiation, water vapor pressure, and precipitation on a half-hour timescale. The active layer data include daily soil temperature and soil volumetric water content at five different depths. The permafrost data consist of the ground temperature at 20 different depths up to 28.4 m. The high-quality and long-term datasets are expected to serve as accurate forcing data in land surface models and evaluate remote-sensing products for a broader geoscientific community. The datasets are available from the National Tibetan Plateau/Third Pole Environment Data Center (10.11888/Cryos.tpdc.271838, Wu and Xie, 2021). [ABSTRACT FROM AUTHOR]

Relict permafrost presents an ideal opportunity to understand the impacts of climatic warming on the ground thermal regime since it is characterized by mean annual ground temperature close to 0 °C and relatively thin permafrost. The long-term and continuous observations of permafrost thermal state and climate background are of great importance to reveal the links between the energy balance on hourly to annual timescales, to evaluate the variations of permafrost thermal state over multi-annual periods and to validate the remote sensing dataset. Until now there are few data available in relict permafrost regions although those data are important to understand the impacts of climate changes on permafrost especially in the boundary regions between permafrost and seasonally frozen ground regions. In this study, we present 11 years of meteorological and soil data in a relict permafrost site of the Mahan Mountain on the northeast of the Qinghai-Tibet Plateau. The meteorological data are comprised of air and ground surface temperature, relative humidity, wind speed and direction, shortwave and longwave downward and upward radiation, water vapor pressure, and precipitation on half-an-hour timescale. The active layer data include daily soil temperature and soil moisture at five different depths. The permafrost data consist of ground temperature at twenty different depths up to 28.4 m. The high-quality and long-term datasets are expected to serve as accurate forcing data in land surface models and evaluate remote-sensing products for a broader geoscientific community. The datasets are available from the National Tibetan Plateau/Third Pole Environment Data Center (https://doi.org/10.11888/Cryos.tpdc.271838, Wu and Xie, 2021). [ABSTRACT FROM AUTHOR]

Permafrost on the Qinghai–Tibet Plateau (QTP) has undergone degradation as a result of recent climate change. This may alter the thermo‐hydrological processes and unlock soil organic carbon, and thereby affect local hydrological, ecological, and climatic systems. The relationships between permafrost and climate change have received extensive attention, and in this paper we review climate change for permafrost regions of the QTP over the past 30 years. We summarize the current state and changes in permafrost distribution and thickness, ground temperature, and ground ice conditions. We focus on changes in permafrost thermal state and in active‐layer thickness (ALT). Possible future changes in ground temperature and ALT are also discussed. Finally, we discuss the changes in hydrological processes and to ecosystems caused by permafrost degradation. Air temperature and ground temperature in the permafrost regions of the QTP have increased from 1980 to 2018, and the active layer has been thickening at a rate of 19.5 cm per decade. The response of permafrost to climate change is not as fast as in some reports, and permafrost degradation is slower than projected by models that do not account for conditions deep in permafrost. [ABSTRACT FROM AUTHOR]

Spatial information of particle size fractions (PSFs) is primary for understanding the thermal state of permafrost in the Qinghai-Tibet Plateau (QTP) in response to climate change. However, the limitation of field observations and the tremendous spatial heterogeneity hamper the digital mapping of PSF. This study integrated log-ratio transformation approaches, variable searching methods, and machine learning techniques to map the surficial soil PSF distribution of two typical permafrost regions. Results showed that the Boruta technique identified different covariates but retained those covariates of vegetation and land surface temperature in both regions. Variable selection techniques effectively decreased the data redundancy and improved model performance. In addition, the spatial distribution of soil PSFs generated by four log-ratio models presented similar patterns. Isometric log-ratio random forest (ILR-RF) outperformed the other models in both regions (i.e., R2 ranged between 0.36 to 0.56, RMSE ranged between 0.02 and 0.10). Compared with three legacy datasets, our prediction better captured the spatial pattern of PSFs with higher accuracy. Although this study largely improved the accuracy of spatial distribution of soil PSFs, further endeavors should also be made to improve model accuracy and interpretability for a better understanding of the interaction and processes between environmental predictors and soil PSFs at permafrost regions. [ABSTRACT FROM AUTHOR]

Lakes on the Qinghai–Tibetan Plateau (QTP) have experienced significant changes, especially the prevailing lake expansion since 2000 in the endorheic basin. The influence of permafrost thawing on lake expansion is significant but rarely considered in previous studies. In this study, based on Landsat images and permafrost field data, the spatial-temporal area changes of lakes of more than 5 km2 in the endorheic basin on the QTP during 2000–2017 is examined and the impact of permafrost degradation on lake expansion is discussed. The main results are that permafrost characteristics and its degradation trend have close relationships with lake changes. Lake expansion in the endorheic basin showed a southwest–northeast transition from shrinking to stable to rapidly expanding, which corresponded well with the permafrost distribution from island-discontinuous to seasonally frozen ground to continuous permafrost. A dramatic lake expansion in continuous permafrost showed significant spatial differences; lakes expanded significantly in northern and eastern continuous permafrost with a higher ground ice content but slightly in southern continuous permafrost with a lower ground ice content. This spatial pattern was mainly attributed to the melting of ground ice in shallow permafrost associated with accelerating permafrost degradation. Whereas, some lakes in the southern zones of island-discontinuous permafrost were shrinking, which was mainly because the extended taliks arising from the intensified permafrost degradation have facilitated surface water and suprapermafrost groundwater discharge to subpermafrost groundwater and thereby drained the lakes. Based on observation and simulated data, the melting of ground ice at shallow depths below the permafrost table accounted for 21.2% of the increase in lake volume from 2000 to 2016. [ABSTRACT FROM AUTHOR]

• Cold and thick permafrost develops around the lake regions. • Low ground temperature is associated with high soil water content. • Saline water plays a non-negligible role in the permafrost thermal regime. The Qinghai-Tibet Plateau (QTP) is one of the regions in the world where permafrost and lakes are widely developed. Yet, the current understanding of permafrost characteristics surrounding large alpine lakes is still not clear. Based on the observation of permafrost surrounding Zonag Lake and Yanhu Lake (>100 km2) in the Hoh Xil region since 2012, we first investigated the permafrost characteristics and potential influencing factors around large alpine lakes on the QTP. The results indicate that the large alpine lakes have only a marginal thermal effect on the surrounding permafrost. Except for the sites located at the lake bottom and adjacent to the lakeshore, cold permafrost is extensively developed around the lakes, where the mean annual ground temperature is below −1.0℃, and the permafrost thickness is generally more than 40 m. Moreover, significant differences exist in ground temperature between boreholes located in the Yanhu Lake basin and those outside the basin, which the permafrost temperature in the lake basin is remarkably lower. These phenomena are closely related to the high soil water content around lakes. Statistical results show that ground temperature decreases and permafrost thickness increases gradually with increasing soil water content. The latent heat effects play an important role in the thermal dynamics of permafrost, which can buffer the increase of permafrost temperature under climate warming. Meanwhile, the salinity of water can weaken the thermal erosion effect of the lake on the surrounding permafrost to a certain extent. Overall, the permafrost thermal regime in the lake regions is not only controlled by altitude but also affected by soil water content. This study will provide us with a basis for understanding the state and characteristics of the frozen ground around lakes in the permafrost regions of the QTP, as well as for conducting research on the interaction of frozen ground with lakes and even the atmosphere. [ABSTRACT FROM AUTHOR]

• Reveal the dynamics of soil temperature and soil moisture during the freezing and thawing process. • Demonstrate the characteristics thawing of freezing and thawing processes of active layer. • Analysis the characteristics of coupling of moisture and heat of active layer. Hydro-thermal characteristics of the active layer are critical during freezing-thawing cycles, causing the moisture and heat exchanges between both permafrost and atmosphere in permafrost regions. There is better understanding of these characteristics in high-latitude permafrost areas, while comparatively little is known in the middle-low latitude areas. Here, we used field monitoring data along with statistical models to quantitatively analyze the hydro-thermal dynamics of the freezing-thawing processes at the Tanggula (TGL) site in permafrost regions of Qinghai-Tibetan Plateau (QTP). This combined approach was used to examine the hydro-thermal characteristics in high-altitude permafrost regions. Our results revealed that the duration of the freezing process was much shorter than that of the thawing process. During freezing-thawing processes, the amplitude variation in soil temperature had a significant logarithmic relationship with depth. There was a significant exponential relationship between soil water content at a depth of 5 cm and monthly precipitation. The averaged energy in the active layer consumed for phase change from water to ice was 145.53 MJ/m2. Finally, we analyzed the quantitative hydro-thermal characteristics and influential factors during the freezing and thawing processes; the different hydro-thermal processes occurring in high-altitude permafrost regions were compared with those in high latitude permafrost regions. Collectively, these results offer a perspective on the difference in permafrost across different region and also provide a reference for the parameterization of land surface models. [ABSTRACT FROM AUTHOR]