Mean Annual Ground Temperature Research Articles

Development and Performance of an Adaptive Adfreeze Pile

Field studies and geothermal modelling shows ground cooling below raised buildings in permafrost regions significantly offsets the ground warming impact of climate warming. For an adfreeze pile, the ground cooling below a raised building improves the capacity relative to pre-construction conditions. Many designers do not take credit for this cooling effect but propose to incorporate thermal mitigation in the design, such as the use of thermopiles. The adaptive adfreeze pile is an innovative concept that accounts for long-term cooling beneath raised buildings and the resulting enhanced pile capacity. The concept entails the installation of a closed ended steel pipe as a conventional adfreeze pile. If future ground temperatures warm above a design threshold, a small diameter thermosyphon could be inserted into the interior of the hollow pile. The retrofitted thermosyphon, if ever required, would passively cool the ground during winter to reduce the mean annual ground temperature and maintain pile capacity. This approach is cost-effective compared to conventional thermopile design and provides greater thermosyphon performance assurances in the long-term. This paper details of the application of this pile design for two, multi-story buildings in Old Crow Yukon, and describes the geothermal background showing its technical feasibility and initial performance data.

Post-fire stabilization of thaw-affected permafrost terrain in northern Alaska

In 2007, the Anaktuvuk River fire burned more than 1000 km2 of arctic tundra in northern Alaska, ~ 50% of which occurred in an area with ice-rich syngenetic permafrost (Yedoma). By 2014, widespread degradation of ice wedges was apparent in the Yedoma region. In a 50 km2 area, thaw subsidence was detected across 15% of the land area in repeat airborne LiDAR data acquired in 2009 and 2014. Updating observations with a 2021 airborne LiDAR dataset show that additional thaw subsidence was detected in < 1% of the study area, indicating stabilization of the thaw-affected permafrost terrain. Ground temperature measurements between 2010 and 2015 indicated that the number of near-surface soil thawing-degree-days at the burn site were 3 × greater than at an unburned control site, but by 2022 the number was reduced to 1.3 × greater. Mean annual ground temperature of the near-surface permafrost increased by 0.33 °C/yr in the burn site up to 7-years post-fire, but then cooled by 0.15 °C/yr in the subsequent eight years, while temperatures at the control site remained relatively stable. Permafrost cores collected from ice-wedge troughs (n = 41) and polygon centers (n = 8) revealed the presence of a thaw unconformity, that in most cases was overlain by a recovered permafrost layer that averaged 14.2 cm and 18.3 cm, respectively. Taken together, our observations highlight that the initial degradation of ice-rich permafrost following the Anaktuvuk River tundra fire has been followed by a period of thaw cessation, permafrost aggradation, and terrain stabilization.

Optimizing thermal stability in permafrost regions: A comprehensive evaluation of encapsulated phase change material enhanced energy storage embankments

The melting of permafrost can cause serious damage to road structures. This study prepares a phase change geotextile (PCG) with heat absorption and waterproofing properties and proposes a new type of cooling structure called a phase change energy storage embankment (PCESE). A finite element model of the road is established to quantify the artificial permafrost table (APT), mean annual ground temperature (MAGT) at the bottom of the embankment, and mean daily cooling rate (MDCR) of the asphalt pavement surface under different PCESE structures. This study focuses on exploring the effects of the type of epoxy resin composite phase change material (ERPCM), dosage of ERPCM, and position of the PCG on various indices. The Entropy-TOPSIS method is used to evaluate the comprehensive performance of the PCESE and determine the optimal structure and optimization strategy. The results demonstrate that the addition of PCG to an embankment always improves the APT and MDCR, but does not necessarily reduce the MAGT. The optimal type of ERPCM, dosage of ERPCM, and position of PCG are ERPCM2, 12 kg/m2, and 3.0 m, respectively. The dosage of the ERPCM had the highest positive correlation with comprehensive performance. Considering the distribution of comprehensive performance and coefficient of variation under different structures, the recommended type of ERPCM, dosage of ERPCM, and position of the PCG are ERPCM1, 12 kg/m2, and 2.5 m, respectively.

Spatiotemporal characteristics and variability in the thermal state of permafrost on the Qinghai–Tibet Plateau

AbstractPermafrost degradation on the Qinghai–Tibet Plateau (QTP) has significant impacts on climate, hydrology, and engineering and environmental systems. To understand the temporal and spatial characteristics of permafrost on the QTP, we quantified the variation in active layer thickness (ALT), permafrost thermal state, and future permafrost change under different scenarios using observational data, reanalysis data, and the numerical permafrost model. Generally, ALT ranged from 0.5 to 6.0 m with an average of 2.39 m, and mean annual ground temperature (at a depth of zero annual amplitude for ground temperature) mainly ranged between 0 and −3°C with an average of −0.85°C. The soil temperatures in different layers based on the ERA5‐Land data revealed even stronger increasing trends, for example, 0.245, 0.245, 0.244, and 0.238°C/decade at depths of 0–7, 7–28, 28–100, and 100–289 cm from 1980 to 2021, compared to those during the period from 1960 to 2021, which were 0.153, 0.156, 0.155, and 0.149°C/decade, respectively. The average warming trends in annual mean soil temperature were 0.153 and 0.243°C/decade from 1960 to 2021 and 1980 to 2021, respectively. The average rate of thickening of the ALT among the 10 active layer observation sites was 2.84 cm/year. There was a significant warming trend in ground temperature above ~15 m with warming of 0.063 to 0.120, 0.026 to 0.182, 0.101 to 0.314, and 0.189 to 0.303°C/decade at the QTB01, QTB06, QTB08, and XDTGT sites, respectively, and yearly minimum ground temperatures exhibited stronger warming trends than maximum ground temperatures. In addition, the simulation revealed significant increases in ground temperature at the Xidatan (XDT) and Tanggula (TGL) sites under both historical and future Representative Concentration Pathway (RCP) scenarios, but the increases in ground temperature were significantly greater at TGL than XDT. These findings provide important information for understanding the variability in permafrost degradation processes and improving simulations of permafrost change under climate change on the QTP.

Local-scale heterogeneity of soil thermal dynamics and controlling factors in a discontinuous permafrost region

Abstract In permafrost regions, the strong spatial and temporal variability in soil temperature cannot be explained by the weather forcing only. Understanding the local heterogeneity of soil thermal dynamics and their controls is essential to understand how permafrost systems respond to climate change and to develop process-based models or remote sensing products for predicting soil temperature. In this study, we analyzed soil temperature dynamics and their controls in a discontinuous permafrost region on the Seward Peninsula, Alaska. We acquired one-year temperature time series at multiple depths (at 5 or 10 cm intervals up to 85 cm depth) at 45 discrete locations across a 2.3 km2 watershed. We observed a larger spatial variability in winter temperatures than that in summer temperatures at all depths, with the former controlling most of the spatial variability in mean annual temperatures. We also observed a strong correlation between mean annual ground temperature at a depth of 85 cm and mean annual or winter season ground surface temperature across the 45 locations. We demonstrate that soils classified as cold, intermediate, or warm using hierarchical clustering of full-year temperature data closely match their co-located vegetation (graminoid tundra, dwarf shrub tundra, and tall shrub tundra, respectively). We show that the spatial heterogeneity in soil temperature is primarily driven by spatial heterogeneity in snow cover, which induces variable winter insulation and soil thermal diffusivity. These effects further extend to the subsequent summer by causing variable latent heat exchanges. Finally, we discuss the challenges of predicting soil temperatures from snow depth and vegetation height alone by considering the complexity observed in the field data and reproduced in a model sensitivity analysis.

Accelerating thermokarst lake changes on the Qinghai–Tibetan Plateau

As significant evidence of ice-rich permafrost degradation due to climate warming, thermokarst lake was developing and undergoing substantial changes. Thermokarst lake was an essential ecosystem component, which significantly impacted the global carbon cycle, hydrology process and the stability of the Qinghai–Tibet Engineering Corridor. In this paper, based on Sentinel-2 (2021) and Landsat (1988–2020) images, thermokarst lakes within a 5000 m range along both sides of Qinghai–Tibet Highway were extracted to analyse the spatio-temporal variations. The results showed that the number and area of thermokarst lake in 2021 were 3965 and 4038.6 ha (1 ha = 10,000 m2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{2}$$\\end{document}), with an average size of 1.0186 ha. Small thermokarst lakes (<\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$<\\,$$\\end{document}1 ha) accounted for 85.65% of the entire lake count, and large thermokarst lakes (>\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$>\\,$$\\end{document}10 ha) occupied for 44.92% of the whole lake area. In all sub-regions, the number of small lake far exceeds 75% of the total lake number in each sub-region. R1 sub-region (around Wudaoliang region) had the maximum number density of thermokarst lakes with 0.0071, and R6 sub-region (around Anduo region) had the minimum number density with 0.0032. Thermokarst lakes were mainly distributed within elevation range of 4300 m–5000 m a.s.l. (94.27% and 97.13% of the total number and size), on flat terrain with slopes less than 3∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\\circ$$\\end{document} (99.17% and 98.47% of the total number and surface) and in the north, south, and southeast aspects (51.98% and 50.00% of the total number and area). Thermokarst lakes were significantly developed in warm permafrost region with mean annual ground temperature (MAGT) > − 1.5 ∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\\circ$$\\end{document}C, accounting for 47.39% and 54.38% of the total count and coverage, respectively. From 1988 to 2020, in spite of shrinkage or even drain of small portion of thermokarst lake, there was a general expansion trend of thermokarst lake with increase in number of 195 (8.58%) and area of 1160.19 ha (41.36%), which decreased during 1988–1995 (− 702 each year and − 706.27 ha/yr) and then increased during 1995–2020 (184.96–702 each year and 360.82 ha/yr). This significant expansion was attributed to ground ice melting as rising air temperature at a rate of 0.03–0.04 ∘\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^\\circ$$\\end{document}C/yr. Followed by the increasing precipitation (1.76–3.07 mm/yr) that accelerated the injection of water into lake.

Permafrost Degradation Risk Evaluation in the Qinghai‐Tibet Plateau Under Climate Change Based on Machine Learning Models

AbstractPermafrost in the Qinghai‐Tibet Plateau (QTP) is sensitive to climate warming, but the associated degradation risk still lacks accurate evaluation. To address this issue, machine learning (ML) models are established to simulate the mean annual ground temperature (MAGT) and active layer thickness (ALT), and climate data from shared socioeconomic pathways (SSPs) are prepared for evaluation in the future period. Based on the projections, permafrost is expected to remain relatively stable under the SSP1‐2.6 scenario, and large‐scale permafrost degradation will occur after the 2050s, resulting in area losses of 30.15% (SSP2‐4.5), 58.96% (SSP3‐7.0), and 65.97% (SSP5‐8.5) in the 2090s relative to the modeling period (2006–2018). The average permafrost MAGT (ALT) is predicted to increase by 0.50°C (59 cm), 0.67°C (89 cm), and 0.79°C (97 cm) in the 2090s with respect to the modeling period under the SSP2‐4.5, SSP3‐7.0, and SSP5‐8.5 scenarios, respectively. Permafrost in the Qilian Mountains and Three Rivers Source region are fragile and vulnerable to degradation. In the future period, permafrost on the sunny slopes is more prone to degradation and the sunny‐shade slope effect of permafrost distribution will be further enhanced under climate warming. The lower limit of permafrost distribution is expected to rise by about 100 m in the 2050s under the SSP2‐4.5 scenario. These findings can provide valuable insights about future permafrost changes in the QTP.

Numerical simulation for vibration-induced settlement and permanent deformation accumulation in permafrost subgrades of the Qinghai-Tibet Railway

Train-induced vibrations critically influence permafrost subgrade deformation. This study used ABAQUS secondary development to establish a finite element model of vibration-induced settlement for permafrost subgrades in the Qinghai-Tibet Railway (QTR) based on a cumulative plastic strain model. A numerical simulation method for cumulative vibration-induced settlement prediction considering seasonality, vibration frequency, train types, and global warming was proposed. The scientificity of the simulation was verified by monitoring data. Then, the influences of embankment height, ice-rich permafrost thickness, and initial mean annual ground temperature (MAGT) of the site on cumulative vibration-induced settlement and permanent deformation accumulation in permafrost subgrades were analysed. The study further quantitatively evaluated cumulative dynamic and static deformation in the DK1136 section under various global warming conditions. The results indicate that cumulative vibration-induced settlement primarily occurs near the ice-rich permafrost layer and is significantly influenced by ground temperature. Permanent deformation accumulation increases with increasing embankment height, ice-rich permafrost thickness and initial MAGT of the site. Permanent deformation accumulation primarily results from thaw consolidation of the permafrost layer, with vibration-induced settlement contributing approximately 20 %. For permafrost regions, an optimal railway embankment height of 3–3.5 m and effective mitigation of settlement issues involve lowering the ground temperature and the embankment weight. These findings provide essential insights for subgrade challenges in permafrost regions.

High-resolution assessment of retrogressive thaw slump susceptibility in the Qinghai-Tibet Engineering Corridor

Under the rapidly warming climate in the Arctic and high mountain areas, permafrost is thawing, leading to various hazards at a global scale. One common permafrost hazard termed retrogressive thaw slump (RTS) occurs extensively in ice-rich permafrost areas. Understanding the spatial and temporal distributive features of RTSs in a changing climate is crucial to assessing the damage to infrastructure and decision-making. To this end, we used a machine learning-based model to investigate the environmental factors that could lead to RTS occurrence and create a susceptibility map for RTS along the Qinghai-Tibet Engineering Corridor (QTEC) at a local scale. The results indicate that extreme summer climate events (e.g., maximum air temperature and rainfall) contributes the most to the RTS occurrence over the flat areas with fine-grained soils. The model predicts that 13% (ca. 22,948 km2) of the QTEC falls into high to very high susceptibility categories under the current climate over the permafrost areas with mean annual ground temperature at 10 m depth ranging from −3 to −1 °C. This study provides insights into the impacts of permafrost thaw on the stability of landscape, carbon stock, and infrastructure, and the results are of value for engineering planning and maintenance.

Influence of Climate Warming on the Ground Surface Stability over Permafrost along the Qinghai–Tibet Engineering Corridor

The warming climate has posed a serious threat on ground surface stability. In permafrost regions, ground surface instability may induce engineering and geological disasters, especially for the engineering corridor. It is difficult to evaluate ground surface stability over permafrost because the stability is influenced by various factors in permafrost regions. Many single index models cannot comprehensively evaluate the ground surface stability for permafrost. We, therefore, proposed an evaluation model considering different influential factors based on the trapezoidal fuzzy Analytical Hierarchy Process (AHP) method. And the ground surface stability was calculated and analyzed along the Qinghai–Tibet Engineering Corridor under three climate warming conditions (the slow climate warming, the medium climate warming and the rapid climate warming). The results show that the ground surface stability influential factors, including the mean annual ground temperature, the active layer thickness, and the volume ice content, will be greatly changed with the warming climate. By 2100, the percentage of high-temperature permafrost (−0.5 °C &lt; T ≤ 0 °C) will increase about 29.45% with rapid climate warming. The active layer thickness will have an average thickening rate of about 0.030 m/year. Most of the high ice content permafrost will change to low ice content permafrost. The ground surface stability, therefore, will be greatly changed with the warming climate along the Qinghai–Tibet Engineering Corridor. Compared to the present, the stable area will decrease about 5.28% by 2050 under the slow climate warming. And that is approximately 7.91% and 21.78% under the medium and rapid climate warming, respectively. While in year 2100, the decrement is obviously increased. The stable area will decrease about 11.22% under the slow climate warming and about 17.3% under the medium climate warming. The proportion of stable area, however, has an increasing trend under the rapid climate warming. This phenomenon is mainly caused by the warming climate which can lead to the permafrost being degraded to melting soil. The unstable area is mainly distributed near the Chumaer River high plain, Tuotuohe–Yanshiping, Wudaoliang, Tangula Mountains, and other high-temperature permafrost areas. This paper provides a reference for geological hazard prevention and engineering construction along the Qinghai–Tibet Engineering Corridor.

The first 10 m resolution thermokarst lake and pond dataset for the Lena Basin in the 2020 thawing season

ABSTRACT Climate warming rates in the Arctic are far greater than the global average, exerting stronger impacts on permafrost degradation and thermokarst landform development. Thermokarst lakes and ponds (TLPs), which are widely distributed in the Lena Basin in the Russian Arctic, play a vital role in altering local ecosystem. However, the detailed distribution of TLPs in the Lena Basin still remains poorly known. In this study, we built the first 10 m resolution TLP dataset for the Lena Basin in the 2020 thawing season by utilizing 4902 Sentinel-2 images. A robust mapping workflow was developed and implemented in the Google Earth Engine (GEE) platform. The accuracy assessment demonstrates a satisfactory accuracy (93.63%), and our results exhibit a better consistency with real TLPs than global water body products. A total of 380,477 TLPs (~0.53% of the total surface area of the Lena Basin) were identified, showing an uneven distribution in the five sub-basins. The TLPs were found to be mainly located within plain areas, with an active layer thickness in the range of 80–100 cm. The higher ground ice content and mean annual ground temperature were favorable for TLP development. This dataset will be valuable for investigating the complex interaction between TLPs and permafrost. It will also serve as a baseline product for better incorporating thermokarst processes into permafrost-climate models.

Study on the geothermal environment of urban building in permafrost regions of Northeast China

The geothermal environment of urban buildings is critical to the structural stability of urban buildings in permafrost regions, which is directly related to the safety of human settlements. However, existing studies have not been able to obtain the 3D geothermal field of building subgrades and its evolution during operation, due to a lack of continuous geothermal data. In this study, thermistor sensors were installed inside pile foundations during the construction, providing valuable data for geothermal field analysis. Based on long-term in-situ monitoring data, this paper studied the evolution of the geothermal field of urban building in permafrost regions of Northeast China. The results indicate that excavation and cast-in-place foundation construction cause irreversible degradation of the warm permafrost. When the building is vacant, the subgrade is frozen in the winter, with a maximum frost penetration depth of 6 m. When heated in winter, the frost penetration depth decreases year by year and the ground becomes warmer. The ground temperature within the monitoring depth (i.e., the bearing layer of the pile foundation) increases to above 0 °C. The mean annual ground temperature within the 0–4 m depth of the subgrade increases significantly, while that at depths below 7 m exhibits slight fluctuations. The 3D geothermal field and its evolution of the building subgrade are obtained for the first time. It was also found that the sunny-shady effect induces asymmetry of the geothermal field of the building, which increases the risk of uneven settlement of the building. In addition, the seasonal frost penetration on the northern side reaches 3 m, which can cause frost-heaving damage to buildings. These findings provide scientific evidence for risk assessment, disaster prevention, and control of building in permafrost regions under the scenario of climate warming.

Thermal Regime of Permafrost on the Western Yamal Under Climate Warming

Climate change observed in the Arctic affects all components of the natural environment, including the state of permafrost. The purpose of this study is to quantify the response of permafrost in various landscapes to changing climatic parameters. The results of long-term field observations (1978-2021) of the thermal regime of permafrost on the Western Yamal are presented. Along with the increase in mean annual air temperatures, the mean annual ground temperature over the past 43 years has increased by 1.5-2.2°C. The maximum increase of permafrost temperature values is observed on flat and polygonal tundra, the minimum increase is typical for flooded lake basins. A decrease in the annual permafrost temperature amplitude was revealed. That is caused by a rapid increase in the air temperature of the cold period, an increase in the snow thickness and an increase in soil moisture in the active layer. The shrinking in ground temperature amplitude at a depth of 5 m is 0.5-3.6°C. A trend of reducing depth of zero annual amplitude from 12-18 m (1980) to 13-16 m (2021) has been revealed.

Effects of complex environment on soil thermal regime alteration under crushed-rock embankment structures in the permafrost region on the Roof of the World

The thermal stability of permafrost under complex environment (climate scenarios, permafrost types and regional air temperatures) directly affects the long-term service performance of highway or railway. This study uses a large amount of valuable soil temperature monitoring and simulation data to examine the stability of typical crushed-rock embankments (CREs) along Qinghai-Tibet Railway, which is located in the permafrost region on the Roof of the World. Firstly, a novel numerical model for CREs considering a complex heat transfer environment is established and verified. Then, alteration characteristics of recent-term thermal regime of permafrost across time and space under three CREs are revealed based on a decade of field monitoring data. Finally, long-term thermal regime of permafrost under three CREs under complex environment is analyzed by numerical simulation. Results include: 1) Soil temperature near the ground surface under the three CREs shows a decreasing trend, whereas the overall temperature around the deep permafrost increases over time under a recent climate warming. 2) The warming rate of permafrost under CREs rises with the acceleration of climate scenarios and regional air temperature and the decrease of regional ground temperatures. 3) U-shaped crushed-rock embankment is the most suitable CRE for managing complex environment, especially when the mean annual ground temperature is 0 ∼ − 1 °C or climate scenarios are RCP 2.6 and RCP 4.5. 4) Transition from low-temperature permafrost to warm permafrost is a warning signal of permafrost degradation under climate warming. 5) With an increase of permafrost degradation rate (the thawing and warming rates of permafrost), embankment stability becomes worse. These findings will not only serve as a scientific basis for the embankment damage prevention of the Qinghai-Tibet Railway, but also provide important technical supports for the successful building of infrastructure in permafrost regions under complex environment.

Arctic coastal hazard assessment considering permafrost thaw subsidence, coastal erosion, and flooding

The thawing of permafrost in the Arctic has led to an increase in coastal land loss, flooding, and ground subsidence, seriously threatening civil infrastructure and coastal communities. However, a lack of tools for synthetic hazard assessment of the Arctic coast has hindered effective response measures. We developed a holistic framework, the Arctic Coastal Hazard Index (ACHI), to assess the vulnerability of Arctic coasts to permafrost thawing, coastal erosion, and coastal flooding. We quantified the coastal permafrost thaw potential (PTP) through regional assessment of thaw subsidence using ground settlement index. The calculations of the ground settlement index involve utilizing projections of permafrost conditions, including future regional mean annual ground temperature, active layer thickness, and talik thickness. The predicted thaw subsidence was validated through a comparison with observed long-term subsidence data. The ACHI incorporates the PTP into seven physical and ecological variables for coastal hazard assessment: shoreline type, habitat, relief, wind exposure, wave exposure, surge potential, and sea-level rise. The coastal hazard assessment was conducted for each 1 km2 coastline of North Slope Borough, Alaska in the 2060s under the Representative Concentration Pathway 4.5 and 8.5 forcing scenarios. The areas that are prone to coastal hazards were identified by mapping the distribution pattern of the ACHI. The calculated coastal hazards potential was subjected to validation by comparing it with the observed and historical long-term coastal erosion mean rates. This framework for Arctic coastal assessment may assist policy and decision-making for adaptation, mitigation strategies, and civil infrastructure planning.

Investigating the thermal state of permafrost with Bayesian inverse modeling of heat transfer

Abstract. Long-term measurements of permafrost temperatures do not provide a complete picture of the Arctic subsurface thermal regime. Regions with warmer permafrost often show little to no long-term change in ground temperature due to the uptake and release of latent heat during freezing and thawing. Thus, regions where the least warming is observed may also be the most vulnerable to permafrost degradation. Since direct measurements of ice and liquid water contents in the permafrost layer are not widely available, thermal modeling of the subsurface plays a crucial role in understanding how permafrost responds to changes in the local energy balance. In this work, we first analyze trends in observed air and permafrost temperatures at four sites within the continuous permafrost zone, where we find substantial variation in the apparent relationship between long-term changes in permafrost temperatures (0.02–0.16 K yr−1) and air temperature (0.09–0.11 K yr−1). We then apply recently developed Bayesian inversion methods to link observed changes in borehole temperatures to unobserved changes in latent heat and active layer thickness using a transient model of heat conduction with phase change. Our results suggest that the degree to which recent warming trends correlate with permafrost thaw depends strongly on both soil freezing characteristics and historical climatology. At the warmest site, a 9 m borehole near Ny-Ålesund, Svalbard, modeled active layer thickness increases by an average of 13 ± 1 cm K−1 rise in mean annual ground temperature. In stark contrast, modeled rates of thaw at one of the colder sites, a borehole on Samoylov Island in the Lena River delta, appear far less sensitive to temperature change, with a negligible effect of 1 ± 1 cm K−1. Although our study is limited to just four sites, the results urge caution in the interpretation and comparison of warming trends in Arctic boreholes, indicating significant uncertainty in their implications for the current and future thermal state of permafrost.

Risk Zoning of Permafrost Thaw Settlement in the Qinghai–Tibet Engineering Corridor

The Qinghai–Tibet Plateau is the highest and largest permafrost area in the middle and low latitudes of China. In this region, permafrost thaw settlement is the main form of expressway subgrade disaster. Therefore, the quantitative analysis and regionalization study of permafrost thaw settlement deformation are of great significance for expressway construction and maintenance in the Qinghai–Tibet region. This paper establishes a thaw settlement prediction model using the thaw settlement coefficient and thaw depth. The thaw depth was predicted by the mean annual ground temperatures and active-layer thicknesses using the Radial Basis Function (RBF) neural network model, and the thaw settlement coefficient was determined according to the type of ice content. Further, the distribution characteristics of thaw settlement risk of the permafrost subgrade in the study region were mapped and analyzed. The results showed that the thaw settlement risk was able to be divided into four risk levels, namely significant risk, high risk, medium risk and low risk levels, with the areas of these four risk levels covering 3868.67 km2, 1594.21 km2, 2456.10 km2 and 558.78 km2, respectively, of the total study region. The significant risk level had the highest proportion among all the risk levels and was mainly distributed across the Chumar River Basin, Beiluhe River Basin and Gaerqu River Basin regions. Moreover, ice content was found to be the main factor affecting thaw settlement, with thaw settlement found to increase as the ice content increased.

Effect of permafrost degradation on carbon sequestration of alpine ecosystems

Permafrost degradation profoundly affects carbon storage in alpine ecosystems, and the response characteristics of carbon sequestration are likely to differ at the different stages of permafrost degradation. Furthermore, the sensitivity of different stages of permafrost degradation to climate change is likely to vary. However, related research is lacking so far on the Qinghai-Tibetan Plateau (QTP). To investigate these issues, the Shule River headwaters on the northeastern margin of the QTP was selected. We applied InVEST and Noah-MP land surface models in combination with remote sensing and field survey data to reveal the dynamics of different carbon (vegetation carbon, soil organic carbon (SOC), and ecosystem carbon) pools from 2001 to 2020. A space-for-time analysis was used to explore the response characteristics of carbon sequestration along a gradient of permafrost degradation, ranging from lightly degraded permafrost (H-SP) to severely degraded permafrost (U-EUP), and to analyze the sensitivity of the permafrost degradation gradient to climate change. Our results showed that: (1) the sensitivity of mean annual ground temperature (MAGT) to climatic variables in the U-EUP was stronger than that in the H-SP and S-TP, respectively; (2) rising MAGT led to permafrost degradation, but increasing annual precipitation promoted permafrost conservation; (3) vegetation carbon, SOC, and ecosystem carbon had similar spatial distribution patterns, with their storage decreasing from the mountain area to the valley; (4) alpine ecosystems acted as carbon sinks with the rate of 0.34 Mg‧ha−1‧a−1 during 2001–2020, of which vegetation carbon and SOC accumulations accounted for 10.65 % and 89.35 %, respectively; and (5) the effects of permafrost degradation from H-SP to U-EUP on carbon density changed from promotion to inhibition.

Cascading effects of climate change and wildfire on a subarctic lake: A 20‐year case study of watershed change

AbstractMean annual air temperature has been increasing in Alaska since the 1970s and is expected to continue to increase through the current century, resulting in significant environmental changes (e.g., permafrost thaw, shifts in vegetation community composition and distribution, increased wildfire frequency and severity). Because there is little long‐term monitoring data available on lake ecosystems in the subarctic it is difficult to predict how lakes will respond. Here we present data from an ~20‐year long‐term lake and climate monitoring program in Interior Alaska. A significant portion of the lake catchment was burned by wildfires in 1986 and again in 2004. As a result, much of the vegetation in the lake catchment was converted from spruce‐dominated forest to deciduous forest, indicating likely permafrost degradation. At a nearby monitoring site absent of fire effects, mean annual ground temperatures at 50 and 90 cm warmed significantly from about −2°C to about −1°C over the 20‐year monitoring period. Warming of similar or greater magnitude is inferred at the study site due to fire effects. Lake water analyses before and after the 2004 fire show a significant postfire increase in dissolved organic carbon, total nitrogen, and total phosphorous that persisted for a short period (~3 years) and was followed by small, but significant, increases in specific conductance and ion concentrations. Approximately 15 years postfire sulfate and cation concentrations in the lake increased exponentially due to the development of a groundwater seep near the lake. The seep likely formed as a result of permafrost thaw creating new subsurface flowpaths in response to long‐term climate warming and fire effects. In 2021, specific conductance and sulfate concentrations reached 657 μS/cm and 71 mg/L respectively, exceeding tolerance thresholds of the water lily Nuphar lutea. In 2021, N. lutea beds that had occupied the lake since 1981 were no longer visible. Depending on local catchment characteristics, source waters and flow paths contributing to small subarctic lakes will continue to evolve uniquely in response to climate change and thawing permafrost. This case study shows the cascading effects of warming soil and wildfires on catchment characteristics as well as terrestrial and aquatic vegetation and lake water chemistry.

Elevation dependency of future degradation of permafrost over the Qinghai-Tibet Plateau

Global warming has caused widespread permafrost degradation, but the geographic regularity of permafrost degradation is unknown. Here, we investigated the three-dimensional features of future permafrost degradation on the Qinghai-Tibetan Plateau. Our findings show that permafrost degradation under shared socioeconomic pathways (SSPs) has obvious three-dimensional characteristics. In comparison to latitude and aridity, permafrost degradation is closely related to elevation, i.e. it slows with elevation, a phenomenon known as elevation-dependent degradation. The pattern of elevation-dependent degradation is consistent across four subzones and is strongly linked to thermal conditions that vary with elevation. Under SSP2-4.5, SSP3-7.0, and SSP5-8.5 scenarios, remarkable elevation-dependent warming (EDW) is observed at 3600–4900 m, but changes in mean annual ground temperature of permafrost and EDW as altitude rises are anti-phase. Under any SSP, the magnitude of mean annual air temperature along altitude belts determines the degree of permafrost degradation (R 2 > 0.90). This research provides new insight on the evolution of permafrost.