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Permafrost stability is significantly influenced by the thermal buffering effects of snow and active-layer peat soils. In the warm season, peat soils act as a barrier to downward heat transfer mainly due to their low thermal conductivity. In the cold season, the snowpack serves as a thermal insulator, retarding the release of heat from the soil to the atmosphere. Currently, many global land models overestimate permafrost soil temperature and active layer thickness (ALT), partially due to inaccurate representations of soil organic matter (SOM) density profiles and snow thermal insulation. In this study, we evaluated the impacts of SOM and snow schemes on ALT simulations at pan-Arctic permafrost sites using the Energy Exascale Earth System Model (E3SM) land model (ELM). We conducted simulations at the Circumpolar Active Layer Monitoring (CALM) sites across the pan-Arctic domain. We improved ELM-simulated site-level ALT using a knowledge-based hierarchical optimization procedure and examined the effects of precipitation-phase partitioning methods (PPMs), snow compaction schemes, and snow thermal conductivity schemes on simulated snow depth, soil temperature, ALT, and CO2 fluxes. Results showed that the optimized ELM significantly improved agreement with observed ALT (e.g. RMSE decreased from 0.83 m to 0.15 m). Our sensitivity analysis revealed that snow-related schemes significantly impact simulated snow thermal insulation levels, soil temperature, and ALT. For example, one of the commonly used snow thermal conductivity schemes (quadratic Sturm or SturmQua) generally produced warmer soil temperatures and larger ALT compared to the other two tested schemes. The SturmQua scheme also amplified the model’s sensitivity to PPMs and predicted deeper ALTs than the other two snow schemes under both current and future climates. The study highlights the importance of accurately representing snow-related processes and peat soils in land models to enhance permafrost dynamics simulations.

Permafrost, widely distributed in the Northern Hemisphere, plays a vital role in regulating heat and moisture cycles within ecosystems. In the last four decades, due to global warming, permafrost degradation has accelerated significantly in high latitudes and altitudes. However, the impact of permafrost degradation on vegetation remains poorly understood to date. Based on active layer thickness (ALT) monitoring data, meteorological data and normalized difference vegetation index (NDVI) data, we found that most ALT‐monitored sites in the Northern Hemisphere show an increasing trend in NDVI and ALT. This suggests an overall increase in NDVI from 1980 to 2021 while permafrost degradation has been occurring. Permafrost degradation positively influences NDVI growth, with the intensity of the effects varying across land cover types and permafrost regions. Furthermore, based on Mann‐Kendall trend test, we detected abrupt changes in NDVI and environmental factors, further confirming that there is a strong consistency between the abrupt changes of ALT and NDVI, and the consistency between the abrupt change events of ALT and NDVI is stronger than that of air temperature and precipitation. These findings work toward a better comprehending of permafrost effects on vegetation growth in the context of climate change. Plain Language Summary: Our research focuses on the influence of permafrost degradation on vegetation in high‐latitude and high‐altitude regions of the Northern Hemisphere. By analyzing permafrost monitoring and vegetation data, we have observed a widespread occurrence of permafrost degradation and vegetation greening in recent years across the Northern Hemisphere. Our analysis has revealed a strong connection between permafrost degradation and vegetation greening in permafrost areas, and the impact varies with different vegetation and permafrost types. In addition, we further investigated the consistency of abrupt changes in the vegetation growth with various environmental factors. It can be seen that despite the significant influence of air temperature changes on vegetation growth in permafrost regions of the Northern Hemisphere, the abrupt change of vegetation growth is consistent with the abrupt change in the process of permafrost degradation, indicating that vegetation growth displays a heightened sensitivity to permafrost degradation. These findings provide valuable insights into the ecological consequences of permafrost changes in high‐latitude and high‐altitude areas under the influence of climate change. Key Points: Vegetation in the Northern Hemisphere shows a greening trend, and permafrost shows a degradation trendPermafrost degradation positively influences vegetation growth, with the intensity of the effects varying by vegetation and permafrost typesAbrupt changes in vegetation growth are more consistent with abrupt permafrost degradation than with meteorological factors [ABSTRACT FROM AUTHOR]

Energy harvesting from cleaner sources and preserving the environment from dangerous gasses are presently the key priorities globally to maintain sustainable development. In this context, photovoltaic technology plays a vital role in generating energy from ternary organic solar cells. Ternary organic solar cells display significant potential for achieving outstanding photovoltaic performance compared to binary structures. Over the past few years, significant endeavors to develop novel organic materials have led to a consistent rise in efficiency, surpassing 19% for single-junction devices. In our study, we simulated an inverted ternary organic solar cell (TOSC) structure employing the one-dimensional optical and drift diffusion model and using "Oghma-Nano 8.0.034" software by optimizing the active blend thickness at 80 nm within the structure of ITO/SnO2/PM6:D18:L8-BO/PEDOT:PSS/Ag. We simulated different performance parameters such as EQE, Photo-CELIV, PCE, Jsc, Voc, and FF with different active layer thicknesses ranging from 50 to 200 nm to discover the behavior of the device in terms of efficiency parameters. Furthermore, the structure attained a PCE of 20% for an active layer thickness of 80 nm within a Jsc of 27.2 mA cm−2, a Voc of 0.89 V, and an FF of 82.3%. This approach can potentially be valuable in constructing a highly effective TOSC model in the laboratory. [ABSTRACT FROM AUTHOR]

Here, we elucidate the influence of active layer thickness and defect density on the photovoltaic performance of lead-free CsSn0.5Ge0.5I3 perovskite solar cells (PSCs). We explained the dependence of FF and JSC on the perovskite layer thickness and defect density in terms of the extraction rate and generation rate, identifying the role of charge extraction and recombination in the operation of perovskite solar cells. Our finding revealed that when active layer thickness was varied, the best performance was achieved with a thickness of 0.4 µm, resulting in a PCE of 12.79%, open circuit voltage (VOC) of 0.807 V, FF of 77.42%, and JSC of 20.47 mA/cm2 for the CsSn0.5Ge0.5I3-based PSC. Additionally, the impact of defect density on PSC performance was assessed using the Shockley–Read–Hall recombination model. The degradation of photovoltaic performance was evident as trap density increased, with the PCE dropping from 14.38 to 5.47%. VOC experienced a significant reduction of 40%, while JSC and FF showed drops of 25.3% and 14.6%, respectively. The study emphasizes the importance of optimizing active layer thickness and minimizing trap densities to enhance the performance of lead-free PSCs. [ABSTRACT FROM AUTHOR]

Abstract Permafrost, widely distributed in the Northern Hemisphere, plays a vital role in regulating heat and moisture cycles within ecosystems. In the last four decades, due to global warming, permafrost degradation has accelerated significantly in high latitudes and altitudes. However, the impact of permafrost degradation on vegetation remains poorly understood to date. Based on active layer thickness (ALT) monitoring data, meteorological data and normalized difference vegetation index (NDVI) data, we found that most ALT‐monitored sites in the Northern Hemisphere show an increasing trend in NDVI and ALT. This suggests an overall increase in NDVI from 1980 to 2021 while permafrost degradation has been occurring. Permafrost degradation positively influences NDVI growth, with the intensity of the effects varying across land cover types and permafrost regions. Furthermore, based on Mann‐Kendall trend test, we detected abrupt changes in NDVI and environmental factors, further confirming that there is a strong consistency between the abrupt changes of ALT and NDVI, and the consistency between the abrupt change events of ALT and NDVI is stronger than that of air temperature and precipitation. These findings work toward a better comprehending of permafrost effects on vegetation growth in the context of climate change.

Climate warming is leading to rapid changes in land cover types and vegetation biomass in the permafrost regions of the Northern Hemisphere. However, to what extent of the vegetation growth responding to climate change in different permafrost regions and different land cover types regions is still unknown. The spatial-temporal change of normalized difference vegetation index (NDVI) and its response to climate variables from 2000 to 2021 were analyzed based on Slope trend analysis and Pearson correlation analysis. The results show that about 21. 43% of the NDVI in the permafrost regions shows a significant increasing trend, in which the increasing rates of NDVI in the continuous and discontinuous permafrost regions are 2-3 times higher than that in the sporadic permafrost region. On the monthly scale, about 33. 75% of the NDVI in the permafrost regions shows a significant increasing trend in June, with the fastest increasing rates in continuous permafrost regions and scrub vegetation type regions. Temperature, precipitation and active layer thickness exhibit a significant increasing trend. while snow cover shows a decreasing trend. Warmer temperatures promote vegetation growth in low-latitude permafrost regions such as Russia. Precipitation promotes vegetation growth in some specific arid zones such as Mongolian Plateau, but has a negative effect in the central Russia and the southern Canada. Snowpack promotes vegetation growth in areas with low snow cover, such as the southern Russia, but has a negative effect in areas with high snow cover, such as the Arctic. In general, the vegetation within the permafrost region of the Northern Hemisphere is experiencing an overall growth trend, and that warmer temperatures are still the main controlling factor for vegetation growth in the permafrost region of the Northern Hemisphere. The increase in the active layer thickness contributes to the accelerated growth of vegetation in permafrost regions such as the northern Russia. In addition, the growth of NDVI in different permafrost types exhibits noticeable monthly variations, highlighting the need to consider these differences in future developments and improvements of vegetation models. [ABSTRACT FROM AUTHOR]

Permafrost 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. [ABSTRACT FROM AUTHOR]

This research presents a comprehensive environmental assessment of a small mountain permafrost catchment of the Anmangynda River in the Upper Kolyma Highland (Northeastern Asia) over the period of 2021–2023. The study reveals significant diversity in climatic, geocryological, and hydrogeological conditions within this confined area, emphasizing the need for extensive field data collection and monitoring in vast permafrost regions with limited data availability. Key findings include variations in ground temperature, maximum seasonal thaw depth, and depths of zero annual amplitudes of ground temperature at different elevations and landscape types. Groundwater and surface flow dynamics within spring aufeis basins exhibit complex geocryological regimes influenced by icing processes. The presence of aufeis and its impact on local hydrology highlight the ecological significance of this phenomenon. Future research should focus on long-term trends in permafrost dynamics and their relationship with climate change, as well as the ecological effects of aufeis formation on local ecosystems. The study underscores the importance of a multi-faceted approach to environmental assessment, incorporating various environmental parameters and processes, to gain a comprehensive understanding of the intricate interactions within the cryosphere and their responses to changing climate conditions. Such knowledge is essential for addressing broader questions related to climate change, ecosystem resilience, and sustainable resource management in Northeastern Siberia. [ABSTRACT FROM AUTHOR]

The freezing index (FI) is one of the most important indicators that shows the variation of permafrost. However, the relationship between climate change and the thermal conditions of permafrost is not understood well. This study analyzed the variation of FI based on 5-cm soil temperature derived from 74 meteorological stations from 1977 to 2016 on the Qinghai-Tibet Plateau (QTP). Furthermore, the factors affecting the FI variation and its relationship with permafrost degradation were also discussed. The results showed that FI was much smaller in the interior than other areas of the QTP, and it increased at a rate of 53.0 °C d/10a during the 40 years. FI in the main body of the QTP was relatively stable than surrounding areas; it was more stable in the northern part than in the southern part. On average, the FI variation coefficient was larger than 10%, indicating the large fluctuation of FI during the 40 years. FI decreased with the increasing altitude; it was more sensitive to the altitude in the south of 33° N than in the north. The variation of FI was closely related to the maximum freezing depth (MFD) and the active layer thickness (ALT). It was observed that MFD decreased and ALT increased by approximately 1.4 cm and 1.6 cm, respectively, with each 10.0 °C d increase in FI. The results exhibited the thermal condition variation of the permafrost in QTP and revealed a degrading trend of the permafrost. [ABSTRACT FROM AUTHOR]

Permafrost 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. Plain Language Summary: In the past decades, the Qinghai‐Tibet Plateau (QTP) warmed at more than twice the global average, and permafrost degradation within this process has become widely acknowledged. To project the possible changes, a combination of climate data from global climate model, machine learning model, and permafrost field observation data were used, based on a comprehensive review of previous studies. The findings indicate that permafrost in the QTP is not expected to undergo significant degradation under the SSP1‐2.6 scenario. However, noticeable permafrost degradation is projected to occur after the 2050s under the SSP2‐4.5, SSP3‐7.0, and SSP5‐8.5 scenarios, particularly in the Qilian Mountains and Three Rivers Source region. It is predicted that permafrost on sunny slopes is more susceptible to degradation under climate warming, and the permafrost area difference between the sunny and shade slopes will be further expanded. The mean annual air temperature of the QTP will rise by about 1.5°C in the 2050s under the SSP2‐4.5 scenario relative to the average between 2006 and 2018, which may lead to a 100 m rise on the low limit of permafrost distribution. Key Points: Permafrost area of the Qinghai‐Tibet Plateau (QTP) is expected to lose by 30.15% (SSP2‐4.5) to 65.97% (SSP5‐8.5) in the 2090sPermafrost in the Qilian Mountains and Three Rivers Source region are fragile and vulnerable to degradationThe lower limit of permafrost distribution in the QTP is forecasted to rise by about 100 m in the 2050s under the SSP2‐4.5 scenario [ABSTRACT FROM AUTHOR]

This study presents data from the first years of permafrost monitoring in boreholes in the French Alps that started at the end of 2009 in the framework of the PermaFrance network. Nine boreholes are instrumented, among which six monitored permafrost temperature and active layer thickness (ALT) over >10 years. Ice‐poor and cold permafrost in high‐elevation north‐facing rock walls has warmed by up to >1°C at 10 m depth over the reference decade (2011–2020), whereas ice‐rich permafrost (rock glacier) temperatures remained stable. ALT has increased at four of the five boreholes for which decadal data are available. Summer 2015 marks a turning point in ALT regime and greatest ALT values were observed in 2022 (available for six boreholes), but thawing intensity did not show an obvious change. At one site with a layer of coarse blocks about 2 m thick, ALT was stable over 2018–2022 and response to the hottest years was dampened. Linear trends suggest an ALT increase of 2 m per decade for some ice‐poor rock walls, independently of their thermal state. The data reveal a variety of permafrost patterns and evolution with significant intraregional and local differences. Snow modulates the response to air temperature signal in various ways, with an important effect on near‐surface temperature trends and ALT: early snow melting in spring favors an ALT increase in rock walls. Maintaining these monitoring systems and understanding the physical processes controlling heterogeneous responses to climate signals is crucial to better assess permafrost dynamics and to adapt to its consequences. [ABSTRACT FROM AUTHOR]

Oxide transistors attract much attention in fields of displays and low‐cost integrated circuits (ICs). In the present work, IZO transistors were fabricated and the effects of active layer thickness on electrical characteristics of IZO transistors were studied. The devices with IZO thickness of 10 nm show the best electrical characteristics with a high on/off current ratio of 3.4×10 8 , a large field‐effect mobility (μFE) of 11.88 cm 2 /Vs, a small subthreshold swing (SS) of 178.10 mV/decade, and a reasonable turn‐on voltage (Von) of ‐0.3 V. It is demonstrated that IZO is a promising active layer material for future displays and IC applications. [ABSTRACT FROM AUTHOR]

Abstract Our knowledge on the responses of permafrost ecosystems to climate warming is critical for assessing the direction and magnitude of permafrost carbon‐climate feedback. However, most of the previous experiments have only been able to warm the air and surface soil, with limited effects on the permafrost temperature. Consequently, it remains challenging to realistically simulate permafrost thawing in terms of increased active layer (a layer freezing and thawing seasonally above permafrost) thickness under climate warming scenarios. Here, we presented the experimental design and warming performance of a novel experiment, Simulate Warming at Mountain Permafrost (SWAMP), the first one to successfully simulate permafrost warming and the subsequent active layer deepening in a swamp meadow situated on the Tibetan Plateau. Infrared heating was employed as above‐ground warming to elevate the temperature of the air and surface soil, and heating rods were inserted vertically in the soil to provide below‐ground warming for transmitting heat to the deep active layer and even to permafrost deposits. In 3 m diameter warmed circular plots, the air and the entire soil profile (from surface soil to 120 cm) was effectively heated, with an increase of approximately 2°C in the upper 60 cm, which progressively weakened with soil depth. Warming increased soil moisture across the growing season by inducing an earlier thawing of the soil. Values varied from 1.8 ± 1.8 to 12.3 ± 2.3% according to the soil depth. Moreover, during the growing season, the warmed plots had greater thaw depths and a deeper active layer thickness of 12.6 ± 0.8 cm. In addition, soil thawing duration was prolonged by the warming, ranging from 22.8 ± 3.3 to 49.3 ± 4.5 days depending on the soil depth. The establishment of SWAMP provides a more realistic simulation of warming‐induced permafrost thaw, which can then be used to explore the effect of climate warming on permafrost ecosystems and the potential permafrost carbon‐climate feedback. Notably, our experiment is more advantageous for investigating how deep soil processes respond to climate warming and active layer deepening, compare with experiments which use passive warming techniques such as open top chambers (OTCs).

The increase in deciduous shrub growth in response to climate change throughout the Arctic tundra has uncertain implications, in part due to a lack of field observations. Here we investigate how increasing alder shrub growth in alpine tundra in Interior Alaska corresponds to active layer thickness and soil physical properties. We documented increased alder growth by combining biomass harvests and dendrochronology with the analysis of remotely sensed Normalized Difference Vegetation Index and fire history. Active layer thickness was measured with a tile probe and carbon and nitrogen pools were assessed via elemental analysis. Shallower organic layers under increasing alder growth indicate that nitrogen-rich, deciduous litter inputs may play a role in accelerating decomposition. Despite the observed reduction in organic carbon stocks, active layer thickness was the same under alder and adjacent graminoid tundra, implying deeper thaw of the underlying mineral soil. This study provides further evidence that the widely observed expansion of deciduous shrubs into graminoid tundra will reduce ecosystem carbon stocks and intensify soil–atmosphere thermal coupling.

Permafrost is an important but poorly known carbon reservoir which is vulnerable to the high latitude accelerated warming. The projected thickening of its superficial seasonally thawed active layer and its induced spatial reorganization will hasten Carbon release in the atmosphere while impacting hydrology, geochemical transfers, vegetation repartition and ground stability. Active layer thickness (ALT) is only assessed by northern stations, therefore, its spatial distribution remains unknown and lacks for model evaluation, especially under the boreal forest. The all-weather spaceborne InSAR technique has shown only partial sensitivity to ALT through ground movements and remained restricted to non-forested areas. To overcome these limitations, we generalized the ground movement estimation under the omnipresent forest by exploiting the SAR polarimetric information, on the one side, and we isolated the thermodynamical component from the hydrological one during freezeback using a land surface model, on the other side, to extract ALT. Based on a one year TerraSAR-X time serie acquired over the region of Yakustk, we obtained a first high resolution ALT image which reveals unexpected short scale spatial heterogeneity, arranged along anisotrotopic patterns. Its poor comparison with the ALT simulated by the ISBA land surface model, currently used in climate modeling, highlights that climate models, and thus their simulations of greenhouse gas emissions, remain very uncertain over northern high latitudes in absence of regionalized ALT information under the boreal forest. This novel approach, operable using current and future sensors over wide areas, offers a new way forward to improve modeling as well as to optimally monitor global warming from the high latitudes.

The soil freezing and thawing process affects soil physical properties, such as heat conductivity, heat capacity, and hydraulic conductivity in frozen ground regions, and further affects the processes of soil energy, hydrology, and carbon and nitrogen cycles. In this study, the calculation of freezing and thawing front parameterization was implemented into the earth system model of the Chinese Academy of Sciences (CAS-ESM) and its land component, the Common Land Model (CoLM), to investigate the dynamic change of freezing and thawing fronts and their effects. Our results showed that the developed models could reproduce the soil freezing and thawing process and the dynamic change of freezing and thawing fronts. The regionally averaged value of active layer thickness in the permafrost regions was 1.92 m, and the regionally averaged trend value was 0.35 cm yr−1. The regionally averaged value of maximum freezing depth in the seasonally frozen ground regions was 2.15 m, and the regionally averaged trend value was −0.48 cm yr−1. The active layer thickness increased while the maximum freezing depth decreased year by year. These results contribute to a better understanding of the freezing and thawing cycle process. [ABSTRACT FROM AUTHOR]

This research presents a comprehensive environmental assessment of a small mountain permafrost catchment of the Anmangynda River in the Upper Kolyma Highland (Northeastern Asia) over the period of 2021–2023. The study reveals significant diversity in climatic, geocryological, and hydrogeological conditions within this confined area, emphasizing the need for extensive field data collection and monitoring in vast permafrost regions with limited data availability. Key findings include variations in ground temperature, maximum seasonal thaw depth, and depths of zero annual amplitudes of ground temperature at different elevations and landscape types. Groundwater and surface flow dynamics within spring aufeis basins exhibit complex geocryological regimes influenced by icing processes. The presence of aufeis and its impact on local hydrology highlight the ecological significance of this phenomenon. Future research should focus on long-term trends in permafrost dynamics and their relationship with climate change, as well as the ecological effects of aufeis formation on local ecosystems. The study underscores the importance of a multi-faceted approach to environmental assessment, incorporating various environmental parameters and processes, to gain a comprehensive understanding of the intricate interactions within the cryosphere and their responses to changing climate conditions. Such knowledge is essential for addressing broader questions related to climate change, ecosystem resilience, and sustainable resource management in Northeastern Siberia.

The increasing warming and humidification have caused the dramatic degradation of Qinghai-Tibet Plateau permafrost. The active layer thickness (ALT) is particularly crucial to be monitored with a wide range as an indispensable variable to characterize permafrost status. Interferometric synthetic aperture radar (InSAR) technology has recently been widely used for ALT retrieval. However, these studies are mostly limited by the accuracy of one-dimensional deformation measurements and ignore the presence of unfrozen water in the negative temperature state of the soil. Therefore, an improved ALT retrieval model using InSAR technology is proposed considering the influence of two-dimensional deformation and unfrozen water. This paper first employed the multidimensional small baseline subset (MSBAS) technology to monitor two-dimensional surface deformation over the Beiluhe-Wudaoliang permafrost region. We observed that the study area underwent surface subsidence of up to 60 mm in the thawing season. Considering the influence of unfrozen water, the ALT was subsequently estimated using the InSAR-observed subsidence. The estimated ALT varied from 50 to 500 cm, with ALT in the Wudaoliang area being higher than that in the Beiluhe Basin. Based on in situ data, the improved method is better than the traditional InSAR-based methods with a mean absolute error of 0.404 m. Our study demonstrates that considering the influence of two-dimensional deformation and unfrozen water can effectively improve the accuracy and reliability of InSAR-based ALT retrieval.

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The thermal state of frozen ground and its changes are important for understanding environmental change and supporting related applications to the Earth’s Third Pole, which is a hotspot area for science research. However, challenges remain in data and modelling, meaning that much information is unavailable, especially for the entire Third Pole region. Here, we provided basic statistical data regarding the current state of frozen ground and its changes over the 1960s–2010s across the entire Third Pole by integrating nearly all currently available ground observation data and high-quality spatial data using machine learning models and existing high-quality frozen ground data products. The results show that the current (2000–2018) areal extents of permafrost and seasonally frozen ground in the Third Pole are approximately 1.27 × 106 km2 (1.15 × 106 to 1.39 × 106 km2) and 2.59 × 106 km2, accounting for 28% and 58%, respectively. The areal extent of permafrost region is approximately 50% (23%–93%) larger than that of permafrost area (land underlain by permafrost), especially in some early maps. The corresponding regional average of the mean annual ground temperature is approximately −1.51 °C (−1.75 to −1.27 °C) in the permafrost area. The regional average of active layer thickness overlying the permafrost and the maximum frost depth for regions of seasonally frozen ground are 235 cm (233–237 cm) and 92 cm, respectively. From the 1960s to the 2010s, on average, permafrost in the Third Pole warmed at a rate of 0.17 °C per decade, which was associated with increases in the maximum thaw depth at a rate of 4.42 cm per decade. The regional average of the maximum frost depth declined at a rate of 2.34 cm per decade over the same period. This synthesis highlights the differences between the two terms (permafrost region and permafrost area) and provides crucial information for frozen ground in the Third Pole with higher accuracy for the scientific community and the public.

As an active ecological agent in the boreal forest, wildfires have many important impacts on the underlying permafrost. However, investigations of post‐fire changes in the features of ecosystem‐protected permafrost are extremely limited in the patchy permafrost regions, Northeast China. Additionally, the impacts of wildfires on patchy permafrost are complicated in this region. In this paper, based on field surveys and observations, permafrost features and their influencing factors were analyzed in the area burned in 2006. The results showed notably lower soil temperatures in shrub‐wetland (NWH1, unburned and NWH2, light burn) in comparison with those in the birch‐larch forest (NWH3, light burn and NWH4, moderate burn). Changes in shallow ground temperatures (0–4 m in depth) were significant. Mean annual soil temperatures (MAST) and annual maximum soil temperature at the light‐burn NWH2 site were 0.3–5.2°C higher than those of unburned NWH1, but annual minimum soil temperatures, 0.3–2.1°C lower. MASTs at the moderately burned NWH4 were 0.6–1.6°C higher than those at the light‐burn NWH3. The active layer thickness (ALT) was greater at burned sites, and; at the moderately burned site, only seasonal frost was found when 13 years after the burn. The contents of soil organic carbon and total nitrogen were the highest at the unburned NWH1 from 0.0 to 0.4 m in depth, followed by those at the lightly‐burned NWH2 and NWH3, and the lowest at the moderately‐burned NWH4. Climate warming, forest fires, and changing local factors (e.g., soil moisture contents, snow cover, soil texture and drainage conditions) worked together to increase ground temperature and ALT. These research results could provide important scientific basis for the protection of boreal forest and wetlands and the ecosystem‐protected permafrost under a warming climate. [ABSTRACT FROM AUTHOR]

Although the power conversion efficiencies (PCEs) of indoor organic photovoltaic (IOPV) continue increasing toward the 30% milestone, important factors (e.g., operation stability and cost potential) for industrial application are neglected, thus resulting in a lack of overall top‐down thinking to evaluate the commercialization potential of IOPVs. By introducing five active layer systems to analyze their efficiency–stability–cost gaps, a standardized indoor industrial figure of merit (i‐FOMindoor) concept is proposed as a reliable approach to evaluate their industrial viability. This i‐FOMindoor contains extracted energy density (including PCE, T80 lifetime, and input power density) and material cost (including synthesis complexity and material usage). To inspire a broader interest, the correlations between active layer thickness, efficiency–stability–cost gap, and i‐FOMindoor are also investigated. Impressively, the levelized cost of energy of IOPVs is less sensitive to the active layer thickness in comparison to the outdoor OPVs. Inspired by this i‐FOMindoor, an outdoor i‐FOM is also proposed for industrial potential evaluation of OPV materials in real external environments. [ABSTRACT FROM AUTHOR]

Hydrologic-land surface models (H-LSMs) provide physically-based understanding and predictions of the current and future states of the world's vast high-latitude permafrost regions. Two major challenges, however, hamper their parametrization and validation when concurrently representing hydrology and permafrost. One is the high computational complexity, exacerbated by the need to include a deep soil profile to adequately capture the freeze/thaw cycles and heat storage. The other is that soil-temperature data are severely limited, and traditional model validation, based on streamflow, can show the right fit to these data for the wrong reasons. There are few observational sites for such vast, heterogeneous regions, and remote sensing provides only limited support. In light of these challenges, we develop 16 parametrizations of a Canadian H-LSM, MESH, for the sub-arctic Liard River Basin and validate them using three data sources: streamflows at multiple gauges, soil temperature profiles from few available boreholes, and multiple permafrost maps. The different parametrizations favor different sources of data and it is challenging to configure a model faithful to all three data sources, which are at times inconsistent with each other. Overall, the results show that: (1) surface insulation through snow-cover primarily regulates permafrost dynamics after model initialization effects decay, relatively long time and (2) different parametrizations yield different partitioning patterns of solid-vs-liquid soil-water and produce different low-flow but similar high-flow regimes. We conclude that, given data scarcity, an ensemble of model parametrizations is essential to provide a reliable picture of the current states and future spatio-temporal co-evolution of permafrost and hydrology. [ABSTRACT FROM AUTHOR]

In this research, simulated solar cell based on cadmium telluride has been investigated to evaluate the effects of different several parameters such as thickness, temperature and illumination on the solar cell performance. The simulated results have revealed an increase in the efficiency with increasing the CdTe thickness. Also, efficiency depends significantly on temperature. Efficiency recorded 19.23% at 100 °C, where the efficiency decreases with increasing the temperature. Also, the efficiency depends on light intensity and light source; results showed that the variation in light intensity will affect the efficiency. [ABSTRACT FROM AUTHOR]

Permafrost stability is significantly influenced by the thermal buffering effects of snow and active-layer peat soils. In the warm season, peat soils act as a barrier to downward heat transfer mainly due to their low thermal conductivity. In the cold season, the snowpack serves as a thermal insulator, retarding the release of heat from the soil to the atmosphere. Currently, many global land models overestimate permafrost soil temperature and active layer thickness (ALT), partially due to inaccurate representations of soil organic matter (SOM) density profiles and snow thermal insulation. In this study, we evaluated the impacts of SOM and snow schemes on ALT simulations at pan-Arctic permafrost sites using the Energy Exascale Earth System Model (E3SM) land model (ELM). We conducted simulations at the Circumpolar Active Layer Monitoring (CALM) sites across the pan-Arctic domain. We improved ELM-simulated site-level ALT using a knowledge-based hierarchical optimization procedure and examined the effects of precipitation-phase partitioning methods (PPMs), snow compaction schemes, and snow thermal conductivity schemes on simulated snow depth, soil temperature, ALT, and CO _2 fluxes. Results showed that the optimized ELM significantly improved agreement with observed ALT (e.g. RMSE decreased from 0.83 m to 0.15 m). Our sensitivity analysis revealed that snow-related schemes significantly impact simulated snow thermal insulation levels, soil temperature, and ALT. For example, one of the commonly used snow thermal conductivity schemes (quadratic Sturm or SturmQua) generally produced warmer soil temperatures and larger ALT compared to the other two tested schemes. The SturmQua scheme also amplified the model’s sensitivity to PPMs and predicted deeper ALTs than the other two snow schemes under both current and future climates. The study highlights the importance of accurately representing snow-related processes and peat soils in land models to enhance permafrost dynamics simulations.

The climate of the Qinghai–Tibet Plateau is distinct. Given the large temperature difference between day and night, drought in perennial years, low rainfall and large evaporation volume, the frozen soil in some areas of the Qinghai–Tibet Plateau will occur in soil salt. The presence of salt in frozen soil salt changes the water thermal characteristics of the frozen soil, which will affect the changes in its activity layer. In this paper, the Beiluhe area of the Qinghai–Tibet Plateau was selected as the research object, and the numerical calculation model of water, heat and salt of salinised frozen soil was established. Considering the influence of salt crystallisation and salt on the freezing temperature of the active layer, the effects of different salt concentrations, water contents and salt type on the temperature of frozen soil and the thickness of the active layer were compared and analysed. Therefore, the salt of soil degenerates frozen soil under the action of sodium chloride and sodium sulphate, and the presence of sodium chloride and sodium sulphate is not conducive to the stability of frozen soil for many years. During soil salinisation, the content of sodium chloride in frozen soil increases; the temperature of permafrost initially decreases and then increases; the initial freezing time of the active layer is postponed in the freezing and cooling stages, the time when the water in the active layer with a salt concentration of 0.2–0.8% was delayed by 21, 32, 54 and 65 days; the temperature of the active layer decreases, which is the opposite in the thawing and heating stages, and the thickness of the active layer increases with the increase in salt concentration. During soil salinisation, the content of sodium sulphate in frozen soil increases; the freezing temperature of the active layer initially decreases and then increases and finally decreases, which is contrary to the temperature of the active layer in the warm season. The thickness of the active layer initially increases (with a maximum increase in 0.82 m) and then decreases and finally increases with the increase in salt concentration. The content of sodium sulphate in frozen soil has little effect on the initial freezing time of the active layer. High water content is conducive to the stability of permafrost. When the content of sodium chloride in frozen soil is constant, the water content increases; the temperature change of frozen soil is smaller; the temperature of the active layer in the warm season is lower; the thickness of the active layer is smaller, and the frozen soil tends to be more stable. When the content of sodium sulphate is constant, the increase in water content generally reduces the warm-season temperature of the active layer and the thickness of the active layer (−6 m the temperature of 30% and 40% water content in −6 m is 0.17 °C and 0.24 °C lower than that of 20% water content). However, analysis of the thickness of the active layer of the frozen soil containing sodium sulphate must combine the influence of water content and freezing temperature. [ABSTRACT FROM AUTHOR]

The hydrothermal dynamics of the active layer is a key issue in the study of surface processes in permafrost regions. Even though the soil energy budget is controlled by thermal conduction and latent heat transfer, few studies have focused on their effects upon the active layer thickness (ALT). In the present study, the community land model (CLM) version 5.0 is used to simulate the soil temperature and moisture of the active layers at the Tanggula (TGL) and Beiluhe (BLH) stations in permafrost regions of the Qinghai–Tibet Plateau based on the theory of soil enthalpy in order to estimate the soil energy state and analyze the energy changes in the active layer during freezing and thawing. The results indicate that the soil enthalpy has significant seasonal variation characteristics, which accurately reflected the freezing and thawing processes of the active layer. The change in soil enthalpy is significantly related to the thawing depth of the active layer in TGL and BLH, and its changing process can be expressed as an exponential relationship. Near the surface, the variation of the energy due to temperature gradient and actual evaporation can also be expressed as an exponential relationship. The promoting effect of heat conduction on the ALT is greater than the inhibiting effect of latent heat transfer, with the energy contribution from the phase change accounting for about 20–40% of the energy due to the temperature gradient. The thawing depth increases by 14.16–18.62 cm as the energy due to the temperature gradient increases by 1 MJ/m2 and decreases by 2.75–7.16 cm as the energy due to the phase change increases by 1 MJ/m2. Thus, the present study quantifies the effects of soil energy upon the ALT and facilitates an understanding of the hydrothermal processes in soils in permafrost regions. [ABSTRACT FROM AUTHOR]

Seasonal subsidence induced by ground ice melt can be measured by interferometric synthetic aperture radar (InSAR) techniques to infer active layer thickness (ALT) in permafrost regions. The magnitude of subsidence depends on both how deep the soil thawed and how much ice/water content existed in the active layer soil. To provide the later, P‐band polarimetric synthetic aperture radar (PolSAR) backscatter is used due to its sensitivity to subsurface soil moisture and freeze/thaw conditions. In this study, which is the second in a two‐part series of Permafrost Dynamics Observatory (PDO), we exploit L‐band InSAR subsidence and P‐band PolSAR backscatter in a joint retrieval scheme to simultaneously estimate ALT and soil moisture profile of permafrost active layer. Both subsidence and backscatter are explicitly characterized by physics‐based models and share a common set of soil parameters including porosity and water saturation profiles. The PDO joint retrieval has been applied to the L‐ and P‐band SAR data acquired by National Aeronautics and Space Administration/Jet Propulsion Laboratory's Uninhabited Aerial Vehicle Synthetic Aperture Radar over Alaska and western Canada during the 2017 Arctic‐Boreal Vulnerability Experiment (ABoVE) airborne campaign. This high‐resolution (30 m) regional estimates of ALT and soil moisture profile spanning over the ABoVE study domain can help link the ground‐based field surveys with satellite observations to further understand the permafrost and active layer soil process dynamics to disturbances and climate change occurring across the northern circumpolar region. Key Points: We develop a joint retrieval scheme for estimating active layer thickness (ALT) and soil moisture in permafrost soils from L‐band interferometric synthetic aperture radar and P‐band polarimetric synthetic aperture radar observationsModeling of synthetic aperture radar (SAR) observables (surface subsidence and radar backscatter) with respect to active layer soil properties is discussedWe present ALT and soil moisture products retrieved from 63 SAR transects acquired during the 2017 NASA Arctic‐Boreal Vulnerability Experiment airborne campaign [ABSTRACT FROM AUTHOR]

This paper presents the results of 30 years of permafrost thermal monitoring in the Tiksi area in the eastern Russian Arctic. At a stone ridge site, the mean annual temperatures in the upper 30 m of the ground have increased by 1–2.4 °C compared to the first years of observations, with trends of °C/yr. At the same time, its change was uneven. In the last 20 years, the rate of increase has increased compared with the first decade of observations. At wet tundra sites in the foothill plain, the mean annual temperatures at the top of permafrost have increased by 2.4–2.6 °C between 2005 and 2022 at rates of 0.11–0.15 °C/yr, and the active layer thicknesses have increased at rates of 0.05–0.41 cm/yr. [ABSTRACT FROM AUTHOR]

The increase in deciduous shrub growth in response to climate change throughout the Arctic tundra has uncertain implications, in part due to a lack of field observations. Here we investigate how increasing alder shrub growth in alpine tundra in Interior Alaska corresponds to active layer thickness and soil physical properties. We documented increased alder growth by combining biomass harvests and dendrochronology with the analysis of remotely sensed Normalized Difference Vegetation Index and fire history. Active layer thickness was measured with a tile probe and carbon and nitrogen pools were assessed via elemental analysis. Shallower organic layers under increasing alder growth indicate that nitrogen-rich, deciduous litter inputs may play a role in accelerating decomposition. Despite the observed reduction in organic carbon stocks, active layer thickness was the same under alder and adjacent graminoid tundra, implying deeper thaw of the underlying mineral soil. This study provides further evidence that the widely observed expansion of deciduous shrubs into graminoid tundra will reduce ecosystem carbon stocks and intensify soil–atmosphere thermal coupling. Two consequences of rapid climate warming in the Arctic, where grass-like plants dominate under very cold conditions, are an increased growth and occurrence of shrubs and associated thaw of frozen ground. This exposes organic matter in soils to microbes that can decompose it into carbonaceous greenhouse gases, but some of this carbon loss may be offset by the increased plant growth. Here, we investigate the impacts of greater shrub presence on soil properties at five sites in Alaska. We documented shrub growth by analyzing satellite images, which can help us understand the productivity and/or leaf coverage at each site back in time, and annual growth rings in shrub stems, which show how old the shrubs are and how much they grow each year. We also measured the depth of soil thaw in the field and its organic matter content in a laboratory. Where shrubs were more common, we found a thinner layer of organic matter at the soil surface. Thaw depth remained the same, which may indicate that the presence of shrubs results in deeper thaw of the mineral soil. Our findings support the hypothesis that shrub expansion will further enhance warming-driven increases of greenhouse gas emissions from Arctic landscapes. Trends in dendrochronology and Normalized Difference Vegetation Index reveal increasing growth of alder shrubs in Interior Alaska. More alder cover results in the loss of the soil organic layer and thus soil C and N that is not offset by more shrub biomass. Increasing alder growth may promote permafrost thaw not captured by tile probe active layer thickness monitoring. [ABSTRACT FROM AUTHOR]

Pipelines are critical infrastructure for Yakutia, transporting vital supplies to communities in this vast northern region. The pipeline routes in central Yakutia traverse areas of ice-rich permafrost that is sensitive to temperature changes. This study examined the thermal state of permafrost in undisturbed and disturbed settings along the Lena River to Mundulakh Reservoir water pipeline and the Mastakh to Yakutsk gas pipeline and considered the effects of climatic fluctuations and surface disturbances (forest removal and wildfire) over the monitoring periods of 28 and 18 years, respectively. The geocryological conditions in the study area, as well as the methods of permafrost thermal monitoring, are described. The observation results demonstrated significant increases in the mean annual ground temperature in the upper permafrost layers, as well as in the active-layer thickness following fire and post-fire clearing. At some sites, progressive deepening of the active layer caused the formation of taliks and reached the top of massive ground ice, initiating permafrost degradation. The development of extreme ground temperatures in the layer of annual temperature fluctuations was analyzed according to the combination of seasonal and annual meteorological conditions and the type of anthropogenic impact. The research results can be extrapolated to similar anthropogenic landscapes. [ABSTRACT FROM AUTHOR]

• Revealed the differences in freeze-thaw processes in different permafrost regions. • Quantified the variability in active layer thickness and mean annual ground temperature in different permafrost regions. • Discussed the reasons for the high variability in permafrost degradation processes over the Northern Hemisphere. Permafrost in the Northern Hemisphere has been degrading under climate change, affecting climatic, hydrological, and ecological systems. To reveal the temporal and spatial characteristics of permafrost degradation under climate change, we quantified permafrost thermal states and active layer thicknesses using observational data covering various periods and different areas of the Northern Hemisphere. The soil temperatures at 20 cm depth in the circumpolar Arctic permafrost regions were much lower than in the Qinghai-Tibet Plateau. The thaw period is 114 days in the circumpolar permafrost regions compared to 167 days in the Qinghai-Tibet Plateau. The active layer thickness (ALT) was largest in transitional permafrost regions and sporadic permafrost regions, and lowest in the high latitude permafrost regions and continuous permafrost regions, and the ALT generally exhibited an increasing trend. The average ALT was 1.7 m, and increased by 3.6 cm per year in the Northern Hemisphere. The mean annual ground temperature (MAGT) was largest in the high-altitude permafrost regions and isolated permafrost regions, and lowest in the high latitude permafrost regions and continuous permafrost regions. The warming rate of the MAGT was largest in the high latitude regions and lowest in the high altitude regions, and gradually increased from isolated permafrost regions to continuous permafrost regions, with an average warming rate of 0.3 °C per decade for the whole Northern Hemisphere. These findings provide important information for understanding the variability in permafrost degradation processes across different regions under climate change. [ABSTRACT FROM AUTHOR]

Abstract Seasonal subsidence induced by ground ice melt can be measured by interferometric synthetic aperture radar (InSAR) techniques to infer active layer thickness (ALT) in permafrost regions. The magnitude of subsidence depends on both how deep the soil thawed and how much ice/water content existed in the active layer soil. To provide the later, P‐band polarimetric synthetic aperture radar (PolSAR) backscatter is used due to its sensitivity to subsurface soil moisture and freeze/thaw conditions. In this study, which is the second in a two‐part series of Permafrost Dynamics Observatory (PDO), we exploit L‐band InSAR subsidence and P‐band PolSAR backscatter in a joint retrieval scheme to simultaneously estimate ALT and soil moisture profile of permafrost active layer. Both subsidence and backscatter are explicitly characterized by physics‐based models and share a common set of soil parameters including porosity and water saturation profiles. The PDO joint retrieval has been applied to the L‐ and P‐band SAR data acquired by National Aeronautics and Space Administration/Jet Propulsion Laboratory's Uninhabited Aerial Vehicle Synthetic Aperture Radar over Alaska and western Canada during the 2017 Arctic‐Boreal Vulnerability Experiment (ABoVE) airborne campaign. This high‐resolution (30 m) regional estimates of ALT and soil moisture profile spanning over the ABoVE study domain can help link the ground‐based field surveys with satellite observations to further understand the permafrost and active layer soil process dynamics to disturbances and climate change occurring across the northern circumpolar region.

Active layer thickness (ALT) of permafrost changes significantly under the combined influence of human activities and climate warming, which has a significant impact on the ecological environment, hydrology, and engineering construction in cold regions. The spatial differentiation of Active layer thickness and its influencing factors have become one of the hot topics in the field of cryopedology in recent years, but there are few studies in the Da Hinggan Ling Prefecture (DHLP). In this study, the Stefan equation was used to simulate the Active layer thickness in the Da Hinggan Ling Prefecture, and the factor detection and interaction detection functions of geodetector were used to analyze the factors affecting the spatial differentiation of Active layer thickness from both natural and humanity aspects. The results showed that Active layer thickness in the Da Hinggan Ling Prefecture ranges from 58.82 cm to 212.55 cm, the determinant coefficient R2, MAE, RMSE between simulation results and the sampling points data were 0.86, 11.25 (cm) and 13.25 (cm), respectively. Lower Active layer thickness values are mainly distributed higher elevations in the west, which are dominated by forest (average ALT: 136.94 cm) and wetlands (average ALT: 71.88 cm), while the higher values are distributed on cultivated land (average ALT: 170.35 cm) and construction land (average ALT: 176.49 cm) in the southeast. Among the influencing factors, elevation is significantly negatively correlated with ALT. followed by summer mean LST, SLHF and snow depth. NDVI and SM has the strong explanation power for the spatial differentiation of ALT in factor detection. Regarding interactions, the explanatory power of slope ∩ snow depth is the highest of 0.83, followed by the elevation ∩ distance to settlements. The results can provide reference for the formulation of ecological environmental protection and engineering construction policies in cold regions.

Active layer thickness (ALT) is a sensitive indicator of response to climate change. ALT has important influence on various aspects of the regional environment such as hydrological processes and vegetation. In this study, 57 ground-penetrating radar (GPR) sections were surveyed along the Qinghai–Tibet Engineering Corridor (QTEC) during 2018–2021, covering a total length of 58.5 km. The suitability of GPR-derived ALT was evaluated using in situ measurements and reference datasets, for which the bias and root mean square error were approximately −0.16 and 0.43 m, respectively. The GPR results show that the QTEC ALT was in the range of 1.25–6.70 m (mean: 2.49 ± 0.57 m). Observed ALT demonstrated pronounced spatial variability at both regional and fine scales. We developed a statistical estimation model that explicitly considers the soil thermal regime (i.e., ground thawing index, TIg), soil properties, and vegetation. This model was found suitable for simulating ALT over the QTEC, and it could explain 52% (R2 = 0.52) of ALT variability. The statistical model shows that a difference of 10 °C.d in T I g is equivalent to a change of 0.67 m in ALT, and an increase of 0.1 in the normalized difference vegetation index (NDVI) is equivalent to a decrease of 0.23 m in ALT. The fine-scale (<1 km) variation in ALT could account for 77.6% of the regional-scale (approximately 550 km) variation. These results provide a timely ALT benchmark along the QTEC, which can inform the construction and maintenance of engineering facilities along the QTEC. [ABSTRACT FROM AUTHOR]

To detect the response of permafrost to climate change in various terrestrial ecosystems, we established a permafrost monitoring network in 2007, which includes eight boreholes to monitor ground temperatures in forest, meadow, steppe, moderately dry steppe, and wetland ecosystems and three Automatic Weather Stations (AWS) to monitor climatic factors, such as wind speed (Ws), air temperature (Ta), relative humidity (RH), precipitation (P), solar radiation (Rs), net radiation (Rn), soil heat flux (SHF), soil temperature (Ts), and soil water content (SWC), in forest, meadow, and steppe ecosystems in north‐central Mongolia. Major indicators, including mean annual ground temperature (MAGT), active layer thickness (ALT), and depth of zero annual amplitude (DZAA), were estimated to detect permafrost degradation. The results show that MAGT has increased by 0.00–0.02°C per year (almost no change) in the ice‐poor permafrost areas and by 0.03–0.06°C per year in the ice‐rich permafrost on pingos and wetlands. ALT showed an annual increase of −0.78 to 0.36 cm (almost no change) in the forest and meadow ecosystems and 2.3–7.2 cm in wetland ecosystems, whereas it increased by 23.0–28.9 cm per year in the steppe ecosystems over the last decade. This implies that the permafrost has degraded more rapidly in the steppe ecosystems than in other ecosystems. Based on correlation analysis, ALT is correlated to P in the meadow ecosystems and to SWC in the forest ecosystem, and MAGT is correlated to RH. However, both ALT and MAGT show a close correlation with major climatic factors, such as Ta, RH, SHF, and SWC in the steppe ecosystem. DZAA shows a close negative correlation with Ta in all ecosystems. These results provide evidence for permafrost degradation and its different responses to climate change in various terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

Late Marine Isotope Stage (MIS) 3 and MIS 2 loess–palaeosol sequences in Western Europe comprise alternating loess layer and 3‐ to 30‐cm‐thick bleached soil horizons with Fe–Mn oxide precipitations, which are usually interpreted as waterlogged active layers and referred to as 'tundra gleys'. Active layer thickness data derived from a regional climate model simulation and the fossils (shells, earthworm granules) found in 'tundra gleys' argue against such an assumption. Most of these horizons better correspond to Fe‐depleted, slightly humic topsoil horizons or subsurface eluvial horizons and should be referred to as (incipient) Ag or Eg horizons. They formed during climate ameliorations associated with vegetation (cryptogams, herbs) development, possibly limited by long‐lasting snow cover. Strong mixing usually occurred in these horizons due to the activity of anecic earthworms and frost activity. [ABSTRACT FROM AUTHOR]

The Nanwenghe Wetlands Reserve in the Yile'huli Mountains is a representative region of the Xing'an permafrost. The response of permafrost to climate change remains unclear due to limited field investigations. Thus, longer-term responses of the ground thermal state to climate change since 2011 have been monitored at four sites with varied surface characteristics: Carex tato wetland (P1) and shrub-C. tato wetland (P2) with a multi-year average temperatures at the depth of zero annual amplitude (TZAA) of −0.52 and −1.19 °C, respectively; Betula platyphylla-Larix gmelinii (Rupr.) Kuzen mixed forest (P3) with TZAA of 0.17 °C, and; the forest of L. gmelinii (Rupr.) Kuzen (P4) with TZAA of 1.65 °C. Continuous observations demonstrate that the ecosystem-protected Xing'an permafrost experienced a cooling under a warming climate. The temperature at the top of permafrost (TTOP) rose (1.8 °C per decade) but the TZAA declined (−0.14 °C per decade), while the active layer thickness (ALT) thinned from 0.9 m in 2012 to 0.8 m in 2014 at P1. Both the TTOP and TZAA increased (0.89 and 0.06 °C per decade, respectively), but the ALT thinned from 1.4 m in 2012 to 0.7 m in 2016 at P2. Vertically detached permafrost at P3 disappeared in summer 2012, with warming rates of +0.42 and + 0.17 °C per decade for TTOP and TZAA, respectively. However, up to date, the ground thermal state has remained stable at P4. We conclude that the thermal offset is crucial for the preservation and persistence of the Xing'an permafrost at the southern fringe.

Wildfires are one of the most important environmental factors controlling forest ecosystem physiology and the carbon balance in the permafrost zone of North Siberia. We investigated tree-ring width (TRW) and stable isotope chronologies in tree-ring cellulose (δ13CCell, δ18OCell) of Larix Gmelinii (Rupr.) Rupr. from a wet (WS) and a dry (DS) site. These sites are characterized by different fire histories (fire in 1852 at the wet and 1896 at the dry sites, respectively). TRW and δ18OCell are identified to be the most sensitive parameters in the changing tree growth conditions after fire. The differences in the soil seasonal thermal regime of sites after fires are shown in the relationship between the studied parameters. The δ13CCell values in tree rings from the two sites are positively correlated independently of the fire impact. This fact indicates that δ13CCell chronologies might be more adequate for climatic reconstruction in the region due to the climate signal consistency. Relationships of δ18OCell values between the two sites are still significantly positive 60 years after the fire impact. Dendroclimatic analysis indicates significant changes in tree-ring growth and isotopic ratio responses to climate due to the increased demand of water for trees during the post-fire period (deeper seasonal subsidence of permafrost). [ABSTRACT FROM AUTHOR]

In the last two decades in Central Yakutia, there has been a significant change in cryogenic landscapes related to climate warming and anthropogenic disturbances. This period is characterized by the activity of forest fires, which significantly impact permafrost landscapes. We observed the dynamics of cryogenic landscapes after a forest fire in 2001 at the Neleger station in Central Yakutia, 35 km northwest of Yakutsk. The observations included ground temperature and active layer thickness monitoring and statements of changes in the soil moisture content of the active layer. Increases in ground temperature, the active layer thickness, and soil moisture content on the burnt site after a forest fire in Neleger station were noted in the first six to seven years after the disturbance. We found that, following forest fires, permafrost progressively restabilizes as forest cover redevelops over time. The results of the studies will become the basis for planning restoration work after forest fires in permafrost landscapes of Central Yakutia. [ABSTRACT FROM AUTHOR]

In boreal and arctic regions, forest fires exert great influences on biogeochemical processes, hydrothermal dynamics of the active layer and near-surface permafrost, and subsequent nutrient cycles. In this article, the studies on impacts of forest fires on the permafrost environment are reviewed. These studies indicate that forest fires could result in an irreversible degradation of permafrost, successions of boreal forests, rapid losses of soil carbon stock, and increased hazardous periglacial landforms. After forest fires, soil temperatures rise; active layer thickens; the release of soil carbon and nitrogen enhances, and; vegetation changes from coniferous forests to broad-leaved forests, shrublands or grasslands. It may take decades or even centuries for the fire-disturbed ecosystems and permafrost environment to return to pre-fire conditions, if ever possible. In boreal forest, the thickness of organic layer has a key influence on changes in permafrost and vegetation. In addition, climate warming, change of vegetation, shortening of fire return intervals, and extent of fire range and increasing of fire severity may all modify the change trajectory of the fire-impacted permafrost environment. However, the observations and research on the relationships and interactive mechanisms among the forest fires, vegetation, carbon cycle and permafrost under a changing climate are still inadequate for a systematic impact evaluation. Using the chronosequence approach of evaluating the temporal changes by measuring changes in the permafrost environment at different stages at various sites (possibly representing varied stages of permafrost degradation and modes), multi-source data assimilation and model predictions and simulations should be integrated with the results from long- and short-term field investigations, geophysical investigations and airborne surveys, laboratory testing and remote sensing. Future studies may enable quantitatively assess and predict the feed-back relationship and influence mechanism among organic layer, permafrost and active layer processes, vegetation and soil carbon under a warming climate at desired spatial and temporal scales. The irreversible changes in the boreal and artic forest ecosystem and their ecological and hydrothermal thresholds, such as those induced by forest fires, should be better and systematically studied.

As the buffer layer between the atmosphere and permafrost, the active layer is vulnerable to climate change. The variation in the active layer thickness (ALT) has important effects on surface energy balance, ecosystem, hydrological cycle, vegetation cover, and engineering construction in permafrost regions. The goal of this study is to discuss the active layer variation under different shared socioeconomic pathways (SSPs) for specific warming levels and to reveal the potential interactions between the ALT and the associated driving factors in typical hydrological basins. We revised the Stefan solution using the edaphic factor and the thawing index calculated by multimodel data from the Coupled Model Intercomparison Project Phase 6 to estimate the variation in the ALT. During 2015 to 2100, the ALT will increase by 14 cm (SSP1‐2.6), 43 cm (SSP2‐4.5), and 1.44 m (SSP5‐8.5), with average increase rates of 2.5 cm/decade, 5.8 cm/decade, and 17.5 cm/decade, respectively. The rates of increase of the ALT in the Hexi basin, Inner basin, Mekong basin, Yangtze basin, and Yellow basin are 12.6 cm/decade, 6.7 cm/decade, 5.2 cm/decade, 8.0 cm/decade, and 5 cm/decade, respectively. These results illustrate that air temperature is the primary determinant of ALT variation and normalized difference vegetation index (NDVI) and snow depth may influence the ALT change. The most significant correlations are between the ALT and NDVI in the Yangtze basin. In different seasons, the spring snow depth has the greatest impact on the ALT in the Hexi basin. Key Points: The modified Stefan solution was used to estimate the active layer thickness (ALT) variation in typical hydrological basins under different shared socioeconomic pathwaysThe ALT exhibits an increasing trend in the Hexi, Inner, Mekong, Yangtze, and Yellow basins, but the trends are spatially heterogeneousChanges in air temperature have stronger control on the ALT than precipitation, snow depth, and normalized difference vegetation index [ABSTRACT FROM AUTHOR]

The climate of the Qinghai–Tibet Plateau is distinct. Given the large temperature difference between day and night, drought in perennial years, low rainfall and large evaporation volume, the frozen soil in some areas of the Qinghai–Tibet Plateau will occur in soil salt. The presence of salt in frozen soil salt changes the water thermal characteristics of the frozen soil, which will affect the changes in its activity layer. In this paper, the Beiluhe area of the Qinghai–Tibet Plateau was selected as the research object, and the numerical calculation model of water, heat and salt of salinised frozen soil was established. Considering the influence of salt crystallisation and salt on the freezing temperature of the active layer, the effects of different salt concentrations, water contents and salt type on the temperature of frozen soil and the thickness of the active layer were compared and analysed. Therefore, the salt of soil degenerates frozen soil under the action of sodium chloride and sodium sulphate, and the presence of sodium chloride and sodium sulphate is not conducive to the stability of frozen soil for many years. During soil salinisation, the content of sodium chloride in frozen soil increases; the temperature of permafrost initially decreases and then increases; the initial freezing time of the active layer is postponed in the freezing and cooling stages, the time when the water in the active layer with a salt concentration of 0.2–0.8% was delayed by 21, 32, 54 and 65 days; the temperature of the active layer decreases, which is the opposite in the thawing and heating stages, and the thickness of the active layer increases with the increase in salt concentration. During soil salinisation, the content of sodium sulphate in frozen soil increases; the freezing temperature of the active layer initially decreases and then increases and finally decreases, which is contrary to the temperature of the active layer in the warm season. The thickness of the active layer initially increases (with a maximum increase in 0.82 m) and then decreases and finally increases with the increase in salt concentration. The content of sodium sulphate in frozen soil has little effect on the initial freezing time of the active layer. High water content is conducive to the stability of permafrost. When the content of sodium chloride in frozen soil is constant, the water content increases; the temperature change of frozen soil is smaller; the temperature of the active layer in the warm season is lower; the thickness of the active layer is smaller, and the frozen soil tends to be more stable. When the content of sodium sulphate is constant, the increase in water content generally reduces the warm-season temperature of the active layer and the thickness of the active layer (−6 m the temperature of 30% and 40% water content in −6 m is 0.17 °C and 0.24 °C lower than that of 20% water content). However, analysis of the thickness of the active layer of the frozen soil containing sodium sulphate must combine the influence of water content and freezing temperature.

The changing thermal state of permafrost is an important indicator of climate change in northern high latitude ecosystems. The seasonally thawed soil active layer thickness (ALT) overlying permafrost may be deepening as a consequence of enhanced polar warming and widespread permafrost thaw in northern permafrost regions (NPRs). The associated increase in ALT may have cascading effects on ecological and hydrological processes that impact climate feedback. However, past NPR studies have only provided a limited understanding of the spatially continuous patterns and trends of ALT due to a lack of long-term high spatial resolution ALT data across the NPR. Using a suite of observational biophysical variables and machine learning (ML) techniques trained with available in situ ALT network measurements ( n = 2966 site-years), we produced annual estimates of ALT at 1 km resolution over the NPR from 2003 to 2020. Our ML-derived ALT dataset showed high accuracy ( R ^2 = 0.97) and low bias when compared with in situ ALT observations. We found the ALT distribution to be most strongly affected by local soil properties, followed by topographic elevation and land surface temperatures. Pair-wise site-level evaluation between our data-driven ALT with Circumpolar Active Layer Monitoring data indicated that about 80% of sites had a deepening ALT trend from 2003 to 2020. Based on our long-term gridded ALT data, about 65% of the NPR showed a deepening ALT trend, while the entire NPR showed a mean deepening trend of 0.11 ± 0.35 cm yr ^−1 [25%–75% quantile: (−0.035, 0.204) cm yr ^−1 ]. The estimated ALT trends were also sensitive to fire disturbance. Our new gridded ALT product provides an observationally constrained, updated understanding of the progression of thawing and the thermal state of permafrost in the NPR, as well as the underlying environmental drivers of these trends.

The Qinghai–Tibet Plateau (QTP) has responded to remarkable climate warming with dramatic permafrost degradation over the past few decades. Previous studies have mostly focused on permafrost responses to rising air temperature, while the effects of accompanying increases in precipitation remain contentious and largely unknown. In this study, a distributed process-based model was applied to quantify the impacts of increased precipitation on permafrost thermal regimes in a warming climate by employing model experiments in the source region of Yellow River (SRYR) on the eastern QTP. The results showed that the active layer thickness (ALT) of permafrost increased by 0.25 m during 2010–2019 compared to 2000 across the SRYR, which was primarily driven by climate warming. In contrast, the increased annual precipitation played a relatively limited role and just slightly mitigated active layer thickening by 0.03 m. Intriguingly, increased precipitation in the cold and warm seasons exerted opposite effects on permafrost across the SRYR. The increased precipitation in the cold season mainly promoted ALT increases, while the increased precipitation in the warm season mitigated ALT increases. In ∼81.0% of the permafrost across the SRYR, the cooling effects of warm season wetting outweighed the warming effects of cold season wetting; while at the transition zone where permafrost was unstable and degrading to seasonally frozen ground, the warming effects of cold season wetting played a relatively larger role which contributed to permafrost degradation. This study explored the physical mechanisms of permafrost thermal responses to climate wetting, thus providing a better understanding of permafrost change in a warmer and wetter climate on the QTP.

Wildfire is recognized as an increasing threat to the southern boreal forests and the permafrost beneath them, with less occurring over the cold continuous permafrost than before. However, we show that continuous permafrost was a major contribution to wildfire expansion in the pan-Arctic over the last two decades. The expansion rate of burned area over continuous permafrost was 0.9 Mha decade ^−1 , in contrast to a decreasing trend (−0.5 Mha decade ^−1 ) over the entire permafrost areas. Burned area has been rapidly growing in the north of the Arctic Circle in particular, where the total burned area in the major fire seasons during 2011–2020 nearly doubled that during 2001–2010. Wildfire expansion is closely linked to an increased soil moisture deficit, considering wildfires there combust more than 90% of belowground fuel. Continuous permafrost experiences more severe fire-induced degradation. Active layer thickening following wildfires over continuous permafrost lasts more than three decades to reach a maximum of more than triple the pre-fire thickness. These new findings highlight the massive expansion of wildfires over continuous permafrost, which can dramatically modify ecological processes, disturb organic carbon stock, and thus accelerate the positive feedback between permafrost degradation and climate warming.

Flooding of low-lying Arctic regions has the potential to warm and thaw permafrost by changing the surface reflectance of solar insolation, increasing subsurface soil moisture, and increasing soil thermal conductivity. However, the impact of flooding on permafrost in the continuous permafrost environment remains poorly understood. To address this knowledge gap, we used a combination of available flooding data on the Ikpikpuk delta and a numerical model to simulate the hydro-thermal processes under coastal floodplain flooding. We first constructed the three most common flood events based on water level data on the Ikpikpuk: snowmelt floods in the late spring and early summer, middle and late summer floods, and floods throughout the whole spring and summer. Then the impact of these flooding events on the permafrost was simulated for one-dimensional permafrost columns using the Advanced Terrestrial Simulator (ATSv1.0), a fully coupled permafrost-hydrology and thermal dynamic model. Our results show that coastal floods have an important impact on coastal permafrost dynamics with a cooling effect on the surficial soil and a warming effect on the deeper soil. Cumulative flooding events over several years can cause continuous warming of the deep subsurface but cool down the surficial layer. Flood timing is a primary control of the vertical extent of the permafrost thaw and the active layer deepening.

Pipelines are critical infrastructure for Yakutia, transporting vital supplies to communities in this vast northern region. The pipeline routes in central Yakutia traverse areas of ice-rich permafrost that is sensitive to temperature changes. This study examined the thermal state of permafrost in undisturbed and disturbed settings along the Lena River to Mundulakh Reservoir water pipeline and the Mastakh to Yakutsk gas pipeline and considered the effects of climatic fluctuations and surface disturbances (forest removal and wildfire) over the monitoring periods of 28 and 18 years, respectively. The geocryological conditions in the study area, as well as the methods of permafrost thermal monitoring, are described. The observation results demonstrated significant increases in the mean annual ground temperature in the upper permafrost layers, as well as in the active-layer thickness following fire and post-fire clearing. At some sites, progressive deepening of the active layer caused the formation of taliks and reached the top of massive ground ice, initiating permafrost degradation. The development of extreme ground temperatures in the layer of annual temperature fluctuations was analyzed according to the combination of seasonal and annual meteorological conditions and the type of anthropogenic impact. The research results can be extrapolated to similar anthropogenic landscapes.