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Multiple proxy records have been used for the understanding of environmental and climate changes during the Holocene. For the first time, we here measure meteoric 10Be isotope of sediments from a drill core collected at the Kunlun Pass (KP) on the northeastern Qinghai-Tibet Plateau (NETP) to investigate mositure and atmospheric circulation changes during the Holocene. The 10Be flux suggests relative low levels in the Early Holocene, followed by a sharp increase to high values at around 4 ka BP (4 ka BP = 4000 years before present). Afterwards, the 10Be flux remains on a high level during the Late Holocene, but decreases slightly towards today. These 10Be deposition patterns are compared to moisture changes in regions dominated by the Indian Summer Monsoon (ISM), East Asian Summer Monsoon (EASM), and the Westerlies. Different from the gradual changes in monsoon patterns, the 10Be data reveal low levels during the Early Holocene until ~4 ka BP when an obvious increase was indicated and a relative high level continues to this day, which is relatively more in agreement with patterns of the Westerlies. This finding provides a new evidence for a shift in the dominant pattern of atmospheric circulation at the KP region from a more monsoonal one to one dominated by the Westerlies. Our results improve the understanding of non-stationary interactions and spatial relevance of the EASM, the ISM and the Westerlies on the Qinghai-Tibet Plateau.

Human activities have substantially altered present-day flow regimes. The Headwater Area of the Yellow River (HAYR, above Huanghe’yan Hydrological Station, with a catchment area of 21,000 km2 and an areal extent of alpine permafrost at ~86%) on the northeastern Qinghai-Tibet Plateau, Southwest China has been undergoing extensive changes in streamflow regimes and groundwater dynamics, permafrost degradation, and ecological deterioration under a warming climate. In general, hydrological gauges provide reliable flow records over many decades and these data are extremely valuable for assessment of changing rates and trends of streamflow. In 1998–2003, the damming of the Yellow River by the First Hydropower Station of the HAYR complicated the examination of the relations between hydroclimatic variables and streamflow dynamics. In this study, the monthly streamflow rate of the Yellow River at Huanghe’yan is reconstructed for the period of 1955–2019 using the double mass curve method, and then the streamflow at Huagnhe’yan is forecasted for the next 20 years (2020–2040) using the Elman neural network time-series method. The dam construction (1998–2000) has caused a reduction of annual streamflow by 53.5–68.4%, and a more substantial reduction of 71.8–94.4% in the drier years (2003–2005), in the HAYR. The recent removal of the First Hydropower Station of the HAYR dam (September 2018) has boosted annual streamflow by 123–210% (2018–2019). Post-correction trends of annual maximum (QMax) and minimum (QMin) streamflow rates and the ratio of the QMax/QMin of the Yellow River in the HAYR (0.18 and 0.03 m3·s−1·yr−1 and −0.04 yr−1, respectively), in comparison with those of precorrection values (−0.11 and −0.004 m3·s−1·yr−1 and 0.001 yr−1, respectively), have more truthfully revealed a relatively large hydrological impact of degrading permafrost. Based on the Elman neural network model predictions, over the next 20 years, the increasing trend of flow in the HAYR would generally accelerate at a rate of 0.42 m3·s−1·yr−1. Rising rates of spring (0.57 m3·s−1·yr−1) and autumn (0.18 m3·s−1·yr−1) discharge would see the benefits from an earlier snow-melt season and delayed arrival of winter conditions. This suggests a longer growing season, which indicates ameliorating phonology, soil nutrient availability, and hydrothermal environments for vegetation in the HAYR. These trends for hydrological and ecological changes in the HAYR may potentially improve ecological safety and water supplies security in the HAYR and downstream Yellow River basins.

Various proxy records have been used for the understanding of environmental and climate variations during the Holocene. Here, for the first time, we use meteoric 10Be isotope measurements performed on sediments from a drill core collected at the Kunlun Pass (KP) on the northeastern Qinghai-Tibet Plateau (NETP) to investigate hydroclimate changes during the Holocene. The 10Be flux suggests relative low levels in the Early Holocene, followed by a sharp increase to high values at around 4 ka BP (4 ka BP = 4000 years before present). Afterwards, the 10Be flux remains on a high level during the Late Holocene, but decreases slightly towards today. These 10Be deposition patterns are compared to moisture changes in regions dominated by the Indian Summer Monsoon (ISM), East Asian Summer Monsoon (EASM), and the Westerlies. Different from the gradual changes in monsoon patterns, the 10Be data reveal low levels during the Early Holocene until ~4 ka BP when an obvious increase is indicated and a relative high level continues to this day, which is relatively more in agreement with patterns of the Westerlies. This finding provides a new evidence for a shift in the dominant pattern of atmospheric circulation at the KP region from a more monsoonal one to one dominated by the Westerlies. Our results improve the understanding of non-stationary interactions and spatial relevance of the EASM, the ISM and the Westerlies on the Qinghai-Tibet Plateau.

Degradation of permafrost with a thin overlying active layer can greatly affect vegetation via changes in the soil water and nutrient regimes within the active layer, while little is known about the presence or absence of such effects in areas with a deep active layer. Here, we selected the northeastern Qinghai-Tibet Plateau as the study area. We examined the vegetation communities and biomass along an active layer thickness (ALT) gradient from 0.6 to 3.5 m. Our results showed that plant cover, below-ground biomass, species richness, and relative sedge cover declined with the deepening active layer, while the evenness, and relative forb cover showed a contrary trend. The vegetation indices and the dissimilarity of vegetation composition exhibited significant changes when the ALT was greater than 2.0 m. The vegetation indices (plant cover, below-ground biomass, evenness index, relative forb cover and relative sedge cover) were closely associated with soil water content, soil pH, texture and nutrient content. Soil water content played a key role in the ALT&ndash, vegetation relationship, especially at depths of 30&ndash, 40 cm. Our results suggest that when the ALT is greater than 2.0 m, the presence of underlying permafrost still benefits vegetation growth via maintaining adequate soil water contents at 30&ndash, 40 cm depth. Furthermore, the degradation of permafrost may lead to declines of vegetation cover and below-ground biomass with a shift in vegetation species.

Reconstructions of the Holocene (especially the mid-Holocene) climatic and environmental changes may serve as an analogue for future scenarios. About 7 ka of Holocene climatic variability in the north of Bayan Har Mountains on the northeastern Tibetan Plateau is reconstructed, using grain size, magnetic susceptibility, geochemical parameters, and accelerator mass spectrometry 14C chronology from peat bog sediments. The peat’s source is found to be aeolian sediments. Climatic variability from the peat bog sediments during the last 7.3 ka can be divided into four stages: warm and wet from 7.3 to 5.7 cal ka BP; cool and dry (semi-wet) from 5.7 to 2.5 cal ka BP; relatively cool and wet from 2.5 to 1.1 cal ka BP; and cold and dry from 1.1 cal ka BP to present. Mid-late Holocene climate in the north of Bayan Har Mountains was significantly unstable during the last 7.3 ka and characterized by five centennial-scale oscillations: 6.2‒6.0, 4.3‒3.9, 2.5‒2.1, 1.7‒1.4, and 0.7‒0.2 cal ka BP. This mid-late Holocene climate recorded by peat bog deposits is consistent with most lacustrine sediment records in the north of Bayan Har Mountains and its adjacent areas. These lacustrine sediments indicated that the climate on the northeastern Tibetan Plateau was warm and humid in the early Holocene, cold and dry after the mid-Holocene (ca. 7.5‒6.0 cal ka BP), and relatively cool and wet in the late Holocene.

Groundwater icings, typical features of permafrost hydrology, are indicative of hydrothermal interactions between surface and ground waters, and permafrost. Their main morphological parameters, i.e., icing area and volume, are generally estimated with low accuracy. Only scarce field observational data on icing volume and seasonal development exist to date. Our study evaluates and compares performance of several widely used techniques of icing morphometric estimation, based on field data, collected on a giant Icing #2 in the Samokit River basin, southern Yakutia. Groundwater icing area was estimated by: (a) staking, (b) unmanned aerial vehicle (UAV) surveys, and (c) satellite imagery analysis. Icing #2 area in late February was between 1.38·106 m2 and 1.68·106 m2, icing volume, between 1.73·106 m3 and 4.20·106 m3, depending on the technique used. Staking is the least accurate, but also the only direct technique, which is hence used as a baseline tool in our study. Staking-based assessment of icing morphometry is the most conservative, while UAV-based estimates of icing area are higher by 14% to 17%, and of icing volume, by 74% to 142%, compared to staking. The latter appears, in our case, to be the least accurate method, although a direct one. It requires a sufficient number of staking points and transects, which should be set up to represent all icing zones, i.e., channel branches and alluvial islands. Photogrammetry based on UAV surveys has numerous advantages, i.e., higher precision of a per pixel icing volume calculation, based on an ice-free valley bottom digital surface model (DSM), and potential reusability of a resulting DSM. However, positioning precision suffers from the overlay of multiple flyovers required because of battery replacements, and, in our case, an insufficient number of ground control points. Satellite imagery along with B.L. Sokolov’s empirical approach were used to estimate the annual maximum icing area and volume, and the empirical estimates tend to converge to satellite-based values. Finally, all thing being equal, UAV-based photogrammetry shows higher precision in estimating the icing morphometrical parameters.

The hydrological regimes of the major rivers in cold regions of the world have changed remarkably since the 1960s, but the mechanisms underlying these changes have not yet been fully understood. Specifically, changes in freeze-thaw processes can affect the thicknesses of the permafrost layer and active layer, storage capacity for liquid water and subsequent surface runoff. In this study, we investigated the hydrological processes and runoff generation in the Yellow River source (YRS) region, which is located in a permafrost region, over the past four decades using ground observations. The impacts of runoff processes are assessed in terms of the spatiotemporal distributions of precipitation, air temperatures, and soil water dynamics in the active layer. The Mann-Kendall test and correlation analysis were employed to detect the variations in runoff and annual changes in influencing factors. Runoff generation in different periods was influenced by different main factors. In the spring flood and recession flow period (SP_FRP, which ranges from late March to mid-June), soil water storage played an important role in runoff generation. With the increased air temperature and enhanced soil ground thawing process, liquid water storage capacity of the soil increased, and constrained runoff. After the soil was saturated in the summer flood and recession flow period (SU_FRP, which ranges from late June to late October), runoff increased with precipitation. In the dry period (DP, which ranges from early November to Mid-March), little precipitation, high potential evaporation (308 mm) and increased air temperature (0.43 °C/decade) caused decreases in snow accumulation and water content. Without a sufficient water supply, river runoff decreased in DP. These results show that precipitation played an important role in runoff generation in SU_FRP. In permafrost regions, the freeze-thaw processes of the active layer of soils, heavy evaporation and the air temperature play primary roles in runoff generation during SP_FRP and DP.

Soil hydrothermal dynamics, resulting from the freezing and thawing processes in the active layer and their influencing factors, were studied in the upper Heihe River Basin (UHRB) in the Qilian Mountains, northeastern Tibetan Plateau. Soil temperature and water content measurements were taken in the active layer of the UHRB in alpine grassland from 2013 to 2014. The results showed that the thaw rate of the active layer was significantly smaller in alpine paludal meadows than the thaw rate in alpine meadows and alpine steppes. This was mainly related to the hydrothermal properties of soils in the active layer, such as moisture content, thermal conductivity, and specific heat. During the thawing process, the active layer soil water content was higher and fluctuated less in alpine paludal meadows. Conversely, the soil water content was lower and fluctuated more significantly in alpine meadows and alpine steppes. These findings could be explained by the prevalence of peat soils, with a low bulk density, and high clay and organic matter content. By contrast, the soil particles in the active layer of alpine meadows and alpine steppes were significantly coarser, with higher bulk density and lower organic matter content. During the freezing process, gravel content and soil texture had a great impact on the unfrozen water content in the frozen soils. However, the factors influencing the soil water retention in frozen soils are complex, and further study is needed. These results provide theoretical support for the evaluation of the hydrological characteristics of the alpine permafrost zone in the Qilian Mountains. Furthermore, the effect of frozen ground on hydrological changes due to climate change in the Heihe River Basin can be simulated and predicted, providing a scientific basis for the ecological conservation of the Qilian Mountains National Park.

Analyses of stable (D and 18O) and radioactive (T) isotopes of different waters were applied to obtain the hydrological information in watersheds with different frozen ground types in the Source Area of the Yellow River, northeastern of Qinghai–Tibet Plateau in 2014 and 2016. Variations of oxygen and hydrogen isotope ratios, statistically higher tritium concentrations and lower water yields in thaw lakes confirm disparate sources of recharges to thaw lakes and other lakes. Thaw lakes at various stages of evolution influence the surface and subsurface water systems differently.

Digital platforms have changed the way in which Asia-Pacific firms operate across borders, however, the impact of digital platforms on entry strategy is under-researched in current International Business literature. This study aims to explore how digital platforms impact New Zealand small and medium-sized (SMEs) companies’ entry into the Chinese market. The results of case study interviews conducted with four SMEs suggest that digital platforms ease entry barriers to some extent, particularly in helping overcome resource constraints and facilitating access to networks. However, the participating firms still required local staff as a key part of successful market entry.

Surface temperature is critical for the simulation of climate change impacts on the ecology, environment, and particularly permafrost in the cryosphere. Virtually, surface temperatures are different in the near-surface air temperature (Ta) measured at a screen-height of 1.5–2 m, the land surface temperature (LST) on the top canopy layer, and the ground surface temperature (GST) 0–5 cm beneath the surface cover. However, not enough attention has been concentrated on the difference in these surface temperatures. This study aims at quantifying the distinction of surface temperatures by the comparisons and numerical simulations of observational field data collected in a discontinuous permafrost region on the northeastern Qinghai-Tibet Plateau (QTP). We compared the hourly, seasonal and yearly differences between Ta, LST, GST, and ground temperatures, as well as the freezing and thawing indices, the N-factors, and the surface and thermal offsets derived from these temperatures. The results showed that the peak hourly LST was reached earliest, closely followed by the hourly Ta. Mean annual LST (MALST) was moderately comparable to mean annual Ta (MAAT), and both were lower than mean annual GST (MAGST). Surface offsets (MAGST-MAAT) were all within 3.5 °C, which are somewhat consistent with other parts of the QTP but smaller than those in the Arctic and Subarctic regions with dense vegetation and thick, long-duration snow cover. Thermal offsets, the mean annual differences between the ground surface and the permafrost surface, were within − 0.3 °C, and one site was even reversed, which may be relevant to equally thawed to frozen thermal conductivities of the soils. Even with identical Ta (comparable to MAAT of − 3.27 and − 3.17 °C), the freezing and thawing processes of the active layer were distinctly different, due to the complex influence of surface characteristics and soil textures. Furthermore, we employed the Geophysical Institute Permafrost Lab (GIPL) model to numerically simulate the dynamics of ground temperature driven by Ta, LST, and GST, respectively. Simulated results demonstrated that GST was a reliable driving indicator for the thermal regime of frozen ground, even if no thermal effects of surface characteristics were taken into account. However, great biases of mean annual ground temperatures, being as large as 3 °C, were induced on the basis of simulations with LST and Ta when the thermal effect of surface characteristics was neglected. We conclude that quantitative calculation of the thermal effect of surface characteristics on GST is indispensable for the permafrost simulations based on the Ta datasets and the LST products that derived from thermal infrared remote sensing.

Carbon fiber-reinforced carbon matrix (C/C) composites are attractive alternative materials for the fabrication of various high-temperature structural components subjected to complex loading conditions. A modified anti-symmetric four-point bending (MAFPB) method for testing a V-notched beam specimen was developed in this study for the investigation of the mechanical behavior of C/C composites under biaxial shear and compression. A finite element model of the specimen was generated to examine the effects of the notch radius and notch spacing on the uniformity and distribution of the stresses in the gauge area. Uniform shear and normal stress were observed in the gauge section of a specimen with a blunted notch and appropriate notch spacing. The three-dimensional (3D) mechanical behaviors of a C/C composite determined by MAFPB tests under pure shear and various biaxial shear–compression stress states were compared with those determined by Iosipescu and off-axis compression experiments. The MAFPB test was found to produce reliable estimates of the mechanical behaviors and failure mechanisms of C/C composites under a wide range of biaxial shear–compression stress states. The shear fracture stress of a 3D C/C composite was particularly observed to significantly decrease with increasing compressive stress component.

Variability of active layer thickness (ALT) in permafrost regions is critical for assessments of climate change, water resources, and engineering applications. Detailed knowledge of ALT variations is also important for studies on ecosystem, hydrological, and geomorphological processes in cold regions. The primary objective of this study is therefore to provide a comprehensive 1971–2000 climatology of ALT and its changes across the entire Northern Hemisphere from 1850 through 2100. To accomplish this, in situ observations, the Stefan solution based on a thawing index, and the edaphic factor (E factor) are employed to calculate ALT. The thawing index is derived from (i) the multimodel ensemble mean of 16 models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) over 1850–2005, (ii) three representative concentration pathways (RCP2.6, RCP4.5, and RCP8.5) for 2006–2100, and (iii) Climatic Research Unit (CRU) gridded observations for 1901–2014. The results show significant spatial variability in in situ ALT that generally ranges from 40 to 320 cm, with some extreme values of 900 cm in the Alps. The differences in the ALT climatology between the three RCPs and the historical experiments ranged from 0 to 200 cm. The biggest increases, of 120–200 cm, are on the Qinghai–Tibetan Plateau, while the smallest increases of less than 20 cm are in Alaska. Averaged over all permafrost regions, mean ALT from CMIP5 increased significantly at 0.57 ± 0.04 cm decade−1 during 1850–2005, while 2006–2100 projections show ALT increases of 0.77 ± 0.08 cm decade−1 for RCP2.6, 2.56 ± 0.07 cm decade−1 for RCP4.5, and 6.51 ± 0.07 cm decade−1 for RCP8.5.

Permafrost degradation on the Qinghai-Tibet Plateau (QTP) will substantially alter the surface runoff discharge and generation, which changes the recharge processes and influences the hydrological cycle on the QTP. Hydrological connections between different water bodies and the influence of thawing permafrost (ground ice) are not well understood on the QTP. This study applied water stable isotopic method to investigate the permafrost hydrological variabilities in Beiluhe Basin (BLB) on Central QTP. Isotopic variations of precipitation, river flow, thermokarst lake, and near-surface ground ice were identified to figure out the moisture source of them, and to elaborate the hydrological connections in permafrost region. Results suggested that isotopic seasonalities in precipitation is evident, it is showing more positive values in summer seasons, and negative values in winter seasons. Stable isotopes of river flow are mainly distributed in the range of precipitation which is indicative of important replenishment from precipitation. δ 18 O, δD of thermokarst lakes are more positive than precipitation, indicating of basin-scale evaporation of lake water. Comparison of δ I values in different water bodies shows that hydrology of thermokarst lakes was related to thawing of permafrost (ground ice) and precipitation. Near-surface ground ice in BLB exhibits different isotopic characteristics, and generates a special δD-δ 18 O relationship (freezing line): δD = 5.81δ 18 O–23.02, which reflects typical freezing of liquid water. From isotopic analysis, it is inferred that near-surface ground ice was mainly recharged by precipitation and active layer water. Stable isotopic and conceptual model is suggestive of striking hydrological connections between precipitation, river flow, thermokarst lake, and ground ice under degrading permafrost. This research provides fundamental comprehensions into the hydrological processes in permafrost regions on QTP, which should be considered in investigating the influence of thawing permafrost on the hydrological cycle on QTP.

The stability of permafrost is of fundamental importance to socio-economic well-being and ecological services, involving broad impacts to hydrological cycling, global budgets of greenhouse gases and infrastructure safety. This study presents a biophysical permafrost zonation map that uses a rule-based geographic information system (GIS) model integrating global climate and ecological datasets to classify and map permafrost regions (totaling 19.76 × 106 km2, excluding glaciers and lakes) in the Northern Hemisphere into five types: climate-driven (CD) (19% of area), CD/ecosystem-modified (41%), CD/ecosystem protected (3%), ecosystem-driven (29%), and ecosystem-protected (8%). Overall, 81% of the permafrost regions in the Northern Hemisphere are modified, driven, or protected by ecosystems, indicating the dominant role of ecosystems in permafrost stability in the Northern Hemisphere. Permafrost driven solely by climate occupies 19% of permafrost regions, mainly in High Arctic and high mountains areas, such as the Qinghai–Tibet Plateau. This highlights the importance of reducing ecosystem disturbances (natural and human activity) to help slow permafrost degradation and lower the related risks from a warming climate.

The electrical resistivity tomography and vegetation surveys were conducted for investigating the distribution of frozen ground and other engineering geological characteristics at four representative sites (BHP, XFB, WLG, and XAZ) along the China-Russia Crude Oil Pipelines (CRCOPs) I and II. The comprehensive analysis shows that CRCOPs play an important role in forming and connecting supra-permafrost subaerial taliks and in facilitating thermokarst landforms, further accelerating permafrost degradation. The survey results indicate that on 15–29 August 2019, the permafrost base under the CRCOP at the XFB site was 21.5 m in depth, that of WLG site was 21.5 m (32.8 m at the undisturbed sites), and that of XAZ site, 37.3 m; the permafrost table of XFB site was 6.72 m (4.97 m on 20 m away from the pipeline), that of WLG site was 8.64 m (1.94 m at the undisturbed sites), and that of XAZ site was 6.72 and 3.38 m on the southern and northern slopes; the hydrothermal influences of CRCOPs extended horizontally to about 60 m away from the pipelines, but the vertical hydrothermal impacts were largely limited to about 10–15 m in depth at the BHP site in the zone of deep (>1.5 m) seasonal frost. The extent of engineering influences from the pipelines and associated engineering activities in patchy and island permafrost are evidently larger than those in seasonal frost. The sites with substantial changes are found in pipeline foundation soils underlain by warm (> − 1 °C; thermally unstable) and ice-rich permafrost. This study can timely help decision makers mitigate frost hazards in a proactive manner.

Regarded as the water towers of numerous large rivers in Asia, the Source Area of Yellow River (SAYR) on Northeast Qinghai-Tibet Plateau (QTP) contains substantial thermokarst lakes, which have exerted significant roles on the regional hydrology and water resources under permafrost degradation. To address the potential impact of climate- and permafrost-induced changes in surface hydrological processes in the SAYR, the hydrological transitions and water balance of thermokarst lakes were characterized on large scales during three years using stable isotope method. Spatial and seasonal deviations in hydrological processes of thermokarst lakes were remarkable. Calculations of evaporation-to-inflow (E/I) ratios based on an isotope-mass balance model revealed substantial evaporation for all thermokarst lakes during June due to the control of climate conditions and limited input water. Substantial feeds from summer/fall rain and permafrost meltwater resulted in lower evaporation and positive water balance of lakes during July, August, September, and October. Based on the relationship between lake-specific input water isotope compositions (δI) and annual average isotope value of precipitation (δP), the recharge patterns of thermokarst lakes in the SAYR were classified: supra-permafrost water/rainfall-dominated lakes were mainly concentrated during June and October regardless of spatial divergences, and summer precipitation/ permafrost thaw-dominated lakes are popular during July and August. Qualitatively, seasonal diversities in the water balance of thermokarst lakes are combinatively controlled by air temperature, precipitation regimes, permafrost degradation in the SAYR. Lastly, the future hydrological trajectories of thermokarst lakes are expected under climatic warming and permafrost degradation. This study serves as an important contribution for understanding future hydrological changes and allocation of water resources on the QTP, as well as an indication of permafrost degradation under climate warming.

Timely and proper backfilling of open-pits in strip coal-mines has been an effective measurement for the recovery of the hydrothermal regimes and ecological environment in permafrost regions. In this study, numerical simulations and statistical regressions were applied for analyzing the recovery processes of the backfill and its major influencing factors for the thermal equilibrium in recently backfilled open pits at the Gulian strip coalmine in Mo'he, Northeast China. Results show that the thermal recovery time of backfilled areas is positively correlated to the backfill depth (BD) of the soils, the backfilled soil temperature (BST), and the mean annual ground surface temperature (MAGST); meanwhile, climate warming can impact on thermal regimes of the backfill area. The impact of climate warming on ground temperature of the backfill will show up significantly in about 50 years after backfilling (BD at 10.0 and 20.0 m, BST at 20.0°C) under the climate warming scenario (CWS) of 0.025°C·year−1. Grey-relation analyses show that the sensitivity of the backfill recovery time declines in the order of the BD, BST and MAGST. On the basis of the abovementioned studies, the layer-by-layer backfilling in cold seasons is advised for more effective and more rapid recovery of thermal regimes of the backfilled open-pits in cold regions.

Study of climatic evolution in the source area of the Yellow River (SAYR) and its mechanisms is of significance for understanding and predicting the climate and environmental changes and permafrost evolution on the northeastern Tibetan Plateau (TP). This study reconstructed the Asian monsoon and climatic evolution in SAYR since 6.1 cal (cal = the calendar year, as below) ka BP in the mid-late Holocene using geochemical parameters (i.e., SiO2/[RO+R2O], SiO2/Al2O3, SiO2/TiO2, SiO2/[Al2O3 + Fe2O3], chemical index of alteration (Al2O3/[Al2O3 + CaO* + Na2O + K2O]), chemical index of weathering (Al2O3/[Al2O3 + CaO* + Na2O]), [CaO + K2O + Na2O]/Al2O3 and K/Na ratios) of peat deposits and AMS 14C chronology. The climate was warm and humid between 6.1 and 5.4 cal ka BP, with weak winter monsoon intensity and strong summer monsoon intensity, and accompanied by strong chemical weathering and leaching. From 5.4 to 1.5 cal ka BP, the climate was relatively cold and dry with enhanced winter monsoon and weakened summer monsoon intensities. During 1.5 and 0.8 cal ka BP, with the winter and summer monsoon changing rapidly, lower winter monsoon intensity, higher summer monsoon intensity, and higher chemical weathering and leaching since 6.1 cal ka BP indicated a warm and humid regional climate. It has been relatively cold and dry as a whole, with a trend of being warm and wet, since 0.8 cal ka BP, accompanied by gradually weakened winter monsoon intensity, gradually enhanced summer monsoon intensity, and gradually enhanced chemical weathering and leaching. The Asian monsoon and climatic evolution process in SAYR is highly unstable and has undergone centennial–millennial scale oscillations since 6.1 cal ka BP. Also, six phases at 6.1–5.9, 4.5–4.2, 2.7–2.4, 1.9–1.7, 1.5–1.4, and 0.6–0.4 cal ka BP correspond with cold events recorded by peat and lacustrine deposits and ice cores on the northeastern and eastern TP and with deep-sea sediments in high-latitude regions in the Northern Hemisphere. The results show that climate change in SAYR on the northeastern TP has been consistent with global climate change since the mid-late Holocene.

Observation data of the hydrothermal processes in the active layer are vital for the verification of permafrost formation and evolution, eco-hydrology, ground-atmosphere interactions, and climate models at various time and spatial scales. Based on measurements of ground temperatures in boreholes, of temperatures and moisture contents of soils in the active layer, and of the mean annual air temperatures at the Qilian, Yeniugou and Tuole meteorological stations in the upper Heihe River Basin (UHRB) and the adjacent areas, a series of observations were made concerning changes in the lower limit of permafrost (LLP) and the related hydrothermal dynamics of soils in the active layer. Because of the thermal diode effect of peat soils, the LLP (at 3600 m) was lower on the northern slope of the Eboling Mountains at the eastern branch of the UHRB than that (at 3650–3700 m) on the alluvial plain at the western branch of the UHRB. The mean temperature of soils at depths of 5 to 77 cm in the active layer on peatlands was higher during periods with subzero temperatures and lower during periods with above-zero temperatures in the vicinity of the LLP on the northern slope of the Eboling Mountains than those at the LLP at the western branch of the UHRB. The thawing and downward freezing rates of soils in the active layer near the LLP on the northern slope of the Eboling Mountains were 0.2 and 1.6 times those found at the LLP at the western branch of the UHRB. From early May to late August, the soil water contents at the depths of 20 to 60 cm in the active layer near the LLP on the northern slope of the Eboling Mountains were significantly lower than those found at the LLP at the western branch of the UHRB. The annual ranges of soil temperatures (ARSTs), mean annual soil temperatures (MASTs) in the active layer on peatlands, and the mean annual ground temperature (MAGT) at a depth of 14 m of the underlying permafrost were all significantly lower near the LLP on the northern slope of the Eboling Mountains. Moreover, the thermophysical properties of peat soils and high moisture contents in the active layer on peatlands resulted in the lower soil temperatures in the active layer close to the LLP on the northern slope of the Eboling Mountains than those found at the LLP at the western branch of the UHRB in the warm season, especially at the deeper depths (20–77 cm). They also resulted in the smaller freezing index (FI) and thawing index (TI) and larger FI/TI ratios of soils at the depths of 5 to 77 cm in the active layer near the LLP on the northern slope of the Eboling Mountains. In short, peatlands have unique thermophysical properties for reducing heat absorption in the warm season and for limiting heat release in the cold season as well. However, the permafrost zone has shrunk by 10–20 km along the major highways at the western branch of the UHRB since 1985, and a medium-scale retrogressive slump has occurred on the peatlands on the northern slope of the Eboling Mountains in recent decades. The results can provide basic data for further studies of the hydrological functions of different landscapes in alpine permafrost regions. Such studies can also enable evaluations and forecasts the hydrological impacts of changing frozen ground in the UHRB and of other alpine mountain regions in West China.

Effective soil thermal conductivity (λ eff) describes the ability of a multiphase soil to transmit heat by conduction under unit temperature gradient. It is a critical parameter for environmental science, earth and planetary science, and engineering applications. Numerous models are available in the literature, but their applicability is generally restricted to certain soil types or water contents (θ). The objective of this study was to develop a new model in the similar form of the Johansen 1975 model to simulate the λ eff(θ) relationship of soils of various soil textures and water contents. An exponential type model with two parameters is developed and a new function for calculating dry soil thermal conductivity is presented. Performance of the new model and six other normalized models were evaluated with published datasets. The results show that the new model is able to well mimic λ eff(θ) relationship of soils from sand to silt loam and from oven dry to full saturation. In addition, it has the best performance among the seven models under test (with root-mean-square error of 0.059 W m−1 °C−1, average deviations of 0.0009 W m−1 °C−1, and Nash–Sutcliffe efficiency of 0.994). The new model has potential to improve the reliability of soil thermal conductivity estimation and be incorporated into numerical modeling for environmental, earth and engineering studies.

Observational data collection on permafrost and active layer freeze–thaw cycle is extremely limited in the upper reaches of the Heihe River (URHHR) in the Qilian Mountains of the north-eastern Qinghai-Tibet Plateau. It acts as a bottleneck, restricting the hydrological effects of the changes in the permafrost and active layer in the Heihe River Basin. Using soil temperature, moisture and air temperature data collected from the four active layer observation sites (AL1, AL3, AL4 and AL7) established in the alpine permafrost regions in the URHHR, from 2013 to 2014, the region's active layer freeze–thaw cycle and the soil hydrothermal dynamics were comparatively analysed. As the elevation increased from 3700 m a.s.l. to 4132 m a.s.l., the mean annual ground temperatures (MAGTs) of the active layer and the active layer thicknesses (ALTs) decreased, the onset date of soil freeze of the active layer occurred earlier and the soil freeze rate increased. However, the onset date of soil thaw and the thaw rate did not exhibit significant trends. Compared to the thaw process, the duration of the active layer freeze process was significantly shortened and its rate was significantly higher. The soil freeze from bottom to top did not occur earlier than that from top to bottom. Furthermore, as elevation increased, the proportion of the bottom-up freeze layer thickness increased. The soil moisture in the thaw layer continuously moved to the freeze front during the active layer's two-way freeze process, causing the thaw layer to be dewatered. The seasonal thaw process resulted in significant reduction of the soil water content in the thaw layer, accounting for the high ice content in the vicinity of the permafrost table. Controlled by elevation, the active layer's seasonal freeze–thaw cycle was also affected by local factors, such as vegetation, slope, water (marsh water and super-permafrost water), lithology and water (ice) content. This study provides quantitative data that identify, simulate and predict the hydrological effects of the changes in the permafrost and active layer of the Heihe River Basin.

The Headwater Region of the Yellow River (HRYR) is the catchment upstream of Duoshi Gorge, covering an area of 29,588 km2. The HRYR is located in the northeastern Tibet Plateau with an altitude higher than 4000 m above sea level, and is especially sensitive to climate change. Since the late 19th century, the mean annual temperature in Tibet Plateau has increased sharply. As a result of increasing air temperature, a significant number of environmental problems have occurred during the past decades, including aeolian desertification. In recent decades, aeolian desertification has become a severe environmental problem in the Tibet Plateau due to permafrost degradation, because permafrost plays an important role in maintaining the grassland vegetation. With the increase in ground temperature, the aeolian activity in the HRYR is likely to become more serious. However, the history of aeolian activity in the HRYR remains unknown due to a lack of chronological studies. In this study, 15 Optical Stimulated Luminescence (OSL) ages from three typical sections were used to reveal the history of aeolian activities in the HRYR during the Holocene. All of the OSL ages were late Holocene, and the oldest age is 2.13 ± 0.16 ka BP. The relative young OSL ages and deep aeolian sediment indicated very high sedimentation rates in the late Holocene, especially after around 1 ka BP. The intensive aeolian activity and low TOC content indicate a drier climate in the late Holocene. The well-sorted sediments and similar grain size distributions of the three sections imply their similar wind regimes. Based on the evolution history of the Yellow River's headward erosion, it is inferred that little aeolian activity occurred in this region during the early and mid-Holocene.

The formation and evolution of permafrost in China during the last 20 ka were reconstructed on the basis of large amount of paleo-permafrost remains and paleo-periglacial evidence, as well as paleo-glacial landforms, paleo-flora and paleofauna records. The results indicate that, during the local Last Glacial Maximum (LLGM) or local Last Permafrost Maximum (LLPMax), the extent of permafrost of China reached 5.3 ´ 106−5.4 ´ 106 km2, or thrice that of today, but permafrost shrank to only 0.80 ´ 106 −0.85 ´ 106 km2, or 50% that of present, during the local Holocene Megathermal Period (LHMP), or the local Last Permafrost Minimum (LLPMin). On the basis of the dating of periglacial remains and their distributive features, the extent of permafrost in China was delineated for the two periods of LLGM (LLPMax) and LHMP (LLPMin), and the evolution of permafrost in China was divided into seven periods as follows: (1) LLGM in Late Pleistocene (ca. 20000 to 13000−10800 a BP) with extensive evidence for the presence of intensive ice-wedge expansion for outlining its LLPMax extent; (2) A period of dramatically changing climate during the early Holocene (10800 to 8500−7000 a BP) when permafrost remained relatively stable but with a general trend of shrinking areal extent; (3) The LHMP in the Mid-Holocene (8500−7000 to 4000−3000 a BP) when permafrost degraded intensively and extensively, and shrank to the LLPMin; (4) Neoglaciation during the late Holocene (4000−3000 to 1000 a BP, when permafrost again expanded; (5) Medieval Warming Period (MWP) in the late Holocene (1000−500 a BP) when permafrost was in a relative decline; (6) Little Ice Age (LIA) in the late Holocene (500−100 a BP), when permafrost relatively expanded, and; (7) Recent warming (during the 20th century), when permafrost continuously degraded and still is degrading. The paleo-climate, geography and paleopermafrost extents and other features were reconstructed for each of these seven periods.

Land use and cover changes (LUCC) in permafrost regions have significant consequences on ecology, engineered systems, and the environment. Obtaining more details about LUCC is crucial for sustainable development, land conservation, and environment management. The Hola Basin (957 km2) in the northernmost part of Northeast China, a boreal forest landscape underlain by discontinuous, sporadic, and isolated permafrost, was selected for the case study. The LUCC was analyzed using the Landsat archive of satellite images from 1973 to 2019. A thematic change detection analysis was performed by combining the object-based image analysis (OBIA) and the Support Vector Machine (SVM) algorithm. Four types of LUCC (forest, grass, water, and anthropic) were extracted with an overall accuracy of 80% for 1973 and >90% for 1986, 2000, and 2019. Forest, the dominant class (750 km2 in 1973), declined by 88 km2 (11.8%) from 1973 to 1986 but had a recovery of 78 km2 (12.5%) from 2000 to 2019. Grass, the second-largest class (187 km2 in 1973), increased by 86 km2 (46.5%) between 1973 and 1986 and decreased by 90 km2 (40%) between 2000 and 2019. The anthropic class continuously increased from 10 km2 (1973) to 37 km2 (2019). Major features in LUCC are attributed to rapid population growth, resource exploitation, agriculture intensification, economic development, and frequent forest fires. Under a pronounced climate warming, these drivers have been accelerating the degradation of permafrost, subsequently triggering natural hazards and deteriorating the ecological environment. This study represents a benchmark for sustainable LUCC management in the Hola Basin, Northeast China.

In cold regions, the occurrence of frozen ground has a fundamental control over the character of the water cycle. To investigate the impact of changing ground temperature conditions on hydrological processes in the context of climate change, a distributed hydrological model with an explicit frozen ground module was applied to an alpine watershed in the upstream area of the Hei'he River in the Qilian Mountains, northwest China. After evaluating the base model, we considered scenarios of frost-free ground and climate change. Results showed that the base model with a frozen ground module successfully captured the water balance and thermal regimes in the basin. When the frozen ground module was turned off, the simulated groundwater recharge and base flow increased by a factor of two to three because surface runoff caused by exceeding infiltration capacities at high elevations, which occurred in the base model, was eliminated. Consequently, the river hydrograph became smoother and flatter, with summer flood peaks delayed and reduced in volume. The annual mean depth where subsurface runoff was generated, was about 2.4 m compared to 1.1 m in the base model. For a warming climate, a combination of increasing evapotranspiration and reducing permafrost area results in smoother and flatter hydrographs, and a reduction in total river discharge. Although our analysis using numerical models has its limitations, it still provides new quantitative understanding of the influences of frozen ground and climate change on hydrological processes in an alpine watershed. Copyright © 2016 John Wiley & Sons, Ltd.

On-site monitoring is very important for understanding formation mechanisms of frost hazards frequently occurring in pipeline foundation soils and for designing and deploying according mitigative measures in permafrost regions. Significant thaw subsidence of ground surfaces along the China-Russia Crude Oil Pipeline (CRCOP) from Mo'he to Daqing, Heilongjiang Province, Northeast China have been observed at some segments underlain by ice-rich, warm (>1.0°C) permafrost since the official operation in January 2011. Recent monitoring results of the thermal states of foundation soils at the kilometer post (KP) 304 site along the CRCOP are presented in this paper. The results indicate that during the period from 2012 to 2014, shallow soils (at the depths from 0.8 to 4.0 m from ground surface) has warmed by approximately 1.0°C in the lateral range of 1.2 to 2.1 m away from the pipeline axis, and deeper permafrost (such as at the depth of 15 m, or the depth of zero annual amplitude of ground temperatures) by 0.08°C per year 4 m away from the pipe axis, and 0.07°C per year 5 m away from the pipeline axis. The results indicate an all-season talik has developed around and along the CRCOP. The thaw bulb, with a faster lateral expansion (compared with the vertical growth), enlarges in summer and shrinks in winter. This research will provide important references and bases for evaluating thermal influences of warm pipeline on permafrost and for design, construction, operation and maintenance of pipelines in permafrost regions.

Accurate estimation of unfrozen/liquid water content (theta(1)) of soils with time domain reflectometry (TDR) is important for understanding freezing and thawing processes and hydrology in cold regions. Empirical equations and composite dielectric mixing models are the two most commonly used methods to estimate water content in unfrozen soils from TDR-measured soil effective permittivity (epsilon(eff)). However, empirical equations derived from unfrozen soil data always overestimate theta(1) in frozen soils and few studies were found to examine the validity of composite dielectric mixing models for measuring theta(1). Therefore, the objective of this study was to evaluate the sensitivities and applicability of composite dielectric mixing models for modeling the epsilon(eff)(theta(1)) relationship. Five multi-phase, composite dielectric mixing models (i.e., power law model, de Loor model, Sihvola discrete model, Sihvola confocal model, and Sphere model) were evaluated with published dataset consisting of independently measured epsilon(eff) and theta(1) on the same samples. The results show that: (1) the power law model and de Loor models are independent of configurations of dielectric mixtures; (2) the Sihvola discrete model depends on the host medium and independent on the configurations of the other components; (3) different dielectric mixing models may end up with the similar epsilon(eff)(theta(1)) relationships by parameter adjusting to represent the same problem; and (4) the de Loor model, and Sihvola discrete and confocal models are most appropriate for modeling the epsilon(eff)(theta(1)) relationship of frozen soils based on the published dataset. This study will significantly contribute to the application of TDR method for liquid water measurement in frozen soils and facilitate the understanding of freezing/thawing processes. (C) 2016 Elsevier B.V. All rights reserved.

Observational data on permafrost and active layer soil hydrothermal processes are extremely limited in the upper reaches of the Heihe River (URHHR) in Qilian Mountains. This lack acts as a bottleneck, restricting the research on the hydrological functions of different landscapes and the hydrological effects of the changes in the permafrost and active layer in the alpine permafrost regions of the Heihe River Basin. The active layer seasonal freeze-thaw processes and the soil hydrothermal dynamics and influencing factors were analyzed using soil temperature and water content observation data of the active layer established on the north slope of Ebo Mountains (NSEBM) in the east branch and in the alluvial plain in the west branch in alpine permafrost regions in the URHHR from 2013 to 2014. The results showed that climatic conditions in the alpine permafrost regions and local factors, such as topography, geomorphology, vegetation, lithology, and soil water content, evidently affected the active layer seasonal freeze-thaw processes and soil hydrothermal dynamics, and the main influence factors also contained snow, water, and winter temperature inversion. The annual surface temperature range (ASTR), mean annual ground temperatures (MAGTs) of the active layer, ground temperature at the bottom of the active layer (TTOP), and MAGT at the depth of zero annual amplitude were lower by 8.8, 0.6 to 1.7 (at depths of 5–77 cm), 0.7, and 0.7°C, respectively, on the NSEBM than at the same elevation in the west branch. Compared with the active layer at the same elevation in the west branch, the active layer onset date of soil thaw on the NSEBM occurred earlier. Moreover, the date reaching the maximum thaw depth occurred later, the duration of the seasonal thaw process was significantly longer, and the rate of the seasonal thaw process was lower. With the later active layer onset date of soil freeze from the ground surface downward, the duration and the rate of the seasonal freeze process on the NSEBM was longer and lower, respectively. Furthermore, the duration of the completely frozen stage on the NSEBM was longer. The active layer onset date of the thaw-rising stage, the relative completely thaw stage, the freeze-fall stage, and the completely frozen stage on the NSEBM lagged significantly from top to bottom, whereas that of the last three stages were evident at the same elevation in the west branch. The rate of change in the active layer soil water content at depths of 20–60 cm at the thaw-rising stage and the freeze-fall stage was both significantly higher on the NSEBM. In addition, the active layer soil water content at the depths of 20–60 cm from the mid- to late completely frozen stage in the beginning of the year to the early thaw-rising stage was lower on the NSEBM. These results were mainly due to the effects of local factors, such as the soil particle composition, dry density, ice content, and organic matter content on the active layer soil water dynamics. This study provides basic data that identify, simulate, and predict the hydrological functions of different landscapes and the hydrological effects of the changes in the permafrost and active layer of the Heihe River Basin. Our study can also provide a reference for the study of seasonal freeze-thaw processes and influencing factors in permafrost regions with different climate types, such as other alpine areas in Western China, the north-eastern Qinghai-Tibet Plateau, Northeast China, and even in the Arctic or sub-Arctic.

The China–Russia Crude Oil Pipeline (CRCOP) was built to transport Siberian crude oil across 1030 km of frozen ground. The Chinese portion of the CRCOP crosses 441 km of discontinuous permafrost zones along the eastern flanks of the Da Xing'anling (Hinggan) Mountains. Significant thaw settlement of some of the pipeline foundation soils has occurred since the pipeline began operating in January 2011. The differential thaw settlement around the pipeline at the transitions between the thaw-settling and thaw-stable zones may lead to displacement or even buckling of the pipeline. To evaluate the engineering safety and long-term stability of pipeline foundations, ground-penetrating radar (GPR) was used to detect the freeze–thaw states of pipeline foundation soils in the permafrost zones. From April 2012 to November 2013, a total of 2780 m of GPR profiles and 62 cross-sections (perpendicular to the CRCOP route) were obtained at eight GPR study sites on various terrains and vegetative coverage, with different thermal insulation configurations around the pipe, and with and without thermosyphons installed. The GPR profiles were interpreted and cross-checked with data from drilling, hand-dug pit or trench excavations, and ground temperature measurements. The results showed that the foundation soils around the pipeline were thawing, with maximum thaw depths under the pipeline of about 1.1 m to 4.5 m from the pipe bottom and increased maximum thaw depths of 0.5 m to 3.7 m during the period of this study. However, GPR profiles from the areas with dense vegetative coverage, and with pipe insulation of 80-mm-thick extruded polystyrene (XPS), and also with vertical thermosyphons installed, showed that permafrost foundation soils were thermally better protected, with only minor thaw settlement. The thermal states of pipeline foundation soils and the underlying permafrost varied markedly with different terrains. The drainage patterns and engineering activities, especially the heating from operating oil flows at an average annual oil temperature of 7.7 °C (with a range of 0.7 °C to 20.4 °C) along the pipeline route may have been responsible for the extensive and substantial thaw subsidence in the ice-rich permafrost zones. Additionally, there was positive feedback between the thaw subsidence of ground surface in the vicinity of the pipeline route and the thaw settlement of the pipeline foundation soils. The greater the earth surface subsidence, the more surface water ponding and soil disturbances, and even more progressive thawing. Therefore, some measures are recommended for stabilizing the pipeline foundation soils. The research results also indicate that the GPR method is effective, nondestructive, and convenient for evaluating the spatiotemporal extent and development processes of the freeze–thaw states of pipeline foundation soils and the underlying permafrost.

Considering the widespread distribution of thermokarst lakes and their significant influence on the hydrological cycle in permafrost regions on the Qinghai–Tibet Plateau (QTP), it is necessary to study their hydrological regimes, which are responding to ongoing climate-induced permafrost thaw. In this paper, water isotopic tracers were used to assess the temporal and interannual hydrological variations and the hydrological processes of two thermokarst lakes (TL-A and TL-B) associated with thawing permafrost in Beiluhe Basin on the QTP. The isotopic results revealed significant differences between the two thermokarst lakes: the TL-A showed more positive isotopic values and small fluctuations than TL-B did. This can be attributed to the hydrological discrepancies between them. Based on the water isotopic mass balance (IMB) model and estimated evaporation, the contributions of permafrost melt water and precipitation to the thermokarst lakes were determined. In both 2011 and 2012, the contributions of thawing permafrost water to thermokarst lakes were of significance, as high as 61.3%. The modeled isotopic composition of input water ( δ I ), and the relationships between climatic factors and lake water isotopes were evaluated. Results suggested that the two lakes originated from multiple sources and confirmed the modeling process well. It also indicated that thawing of permafrost significantly affected the development and hydrological regime of thermokarst lakes on the QTP. It is necessary to emphasize the significant impact of thawing permafrost on the thermokarst lakes on the QTP. Findings demonstrate that ongoing permafrost thaw may have major implications for thermokarst landscapes as climate change continues.

Permafrost is mostly warm and thermally unstable on the Tibetan Plateau (TP), particularly in some marginal areas, thereby being susceptible to degrade or even disappear under climate warming. The degradation of permafrost consequently leads to changes in hydrological cycles associated with seasonal freeze-thaw processes. In this study, we investigated seasonal hydrothermal processes of near-surface permafrost layers and their responses to rain events at two warm permafrost sites in the Headwater Area of the Yellow River, northeastern TP. Results demonstrated that water content in shallow active layers changed with infiltration of rainwater, whereas kept stable in the perennially frozen layer, which serves as an aquitard due to low hydraulic conductivity or even imperviousness. Accordingly, the supra-permafrost water acts as a seasonal aquifer in the thawing period and as a seasonal aquitard in the freezing period. Seasonal freeze-thaw processes in association with rain events correlate well with the recharge and discharge of the supra-permafrost water. Super-heavy precipitation (44 mm occurred on 2 July 2015) caused a sharp increase in soil water content and dramatic rises in soil temperatures by 0.3–0.5 °C at shallow depths and advancement thawing of the active layer by half a month. However, more summer precipitation amount tends to reduce the seasonal amplitude of soil temperatures, decrease mean annual soil temperatures and thawing indices and thin active layers. High salinity results in the long remaining of a large amount of unfrozen water around the bottom of the active layer. We conclude that extremely warm permafrost with TZAA (the temperature at the depth of zero annual amplitude) >−0.5 °C is likely percolated under heavy and super-heavy precipitation events, while hydrothermal processes around the permafrost table likely present three stages concerning TZAA of 0 °C.

Permafrost on the Tibetan Plateau (TP) is controlled by high-elevation and the complex hydrothermal processes and energy balance on the ground surface. To successfully model or map permafrost distribution, it is necessary to parameterize near-surface air or land-surface temperatures (Ta or LST) to ground surface temperature (GST) at local-, meso‑, or macro-scale. Here, a long-term experimental observation (November 2010 to December 2018) was conducted for understanding the differences between Ta and GST at a plot with 26 sites at Chalaping to the south of the Sisters Lakes in the Source Area of the Yellow River, northeastern TP. Results show that GST varies considerably within an area of about 3.5 km2 under the combined thermal influences of surface vegetation, soil moisture conditions, and microtopography. Mean annual GST (MAGST) ranged from –0.55 to –3.02°C, with an average of –1.35±0.63°C. The surface offset varied from 1.01 to 3.90°C, with an average of 2.72±0.70°C. The difference between monthly Ta and monthly GST decreased from 4.64±2.09°C in January to 1.09±1.34°C in July and then gradually increased to 5.61±2.53°C in November. The active layer thickness (ALT) calculated with the ground-surface thawing index ranged from 0.85 to 1.95 m, with an average of 1.51±0.33 m. Annual freezing N-factors and annual thawing N-factors were averaged at 0.58±0.12 and 1.31±0.28, respectively. Although weakly, hourly and daily GST values are positively correlated to NDVI, while ALT negatively correlated with NDVI. This study demonstrates the complex thermal regimes on the ground surface, even within a small area despite the relatively consistent topography. It will likely facilitate the parameterization of the upper thermal boundary of permafrost modeling or mapping on the TP where the landscapes are characterized by extensive presence of dwarf alpine meadow and alpine steppe, further contributing to the study in ecosystem feedbacks to the regional climate change.

In permafrost regions, forest fires actively affect physical and chemical properties of soils. Many studies have been conducted on the effects of forest fires on physical and chemical properties of topsoil, while the research on the fire-induced changes in carbon and other nutrients of soils has received much less attention, particularly that of soils in the active layer and near-surface permafrost. Here, using soil samples from two representative areas (Mangui and Alongshan), we investigated the effects of fires on soil nutrients of larch forest soils in the discontinuous permafrost zone in the northern Da Xing’anling (Hinggan) Mountains, Northeast China. The results showed that soil pH increased with fire severity due to the burning of soil organic matter by more severe fires and leaching of base elements in the residual ash into the soil, and; forest fires resulted in a weakly acidic post-fire soil environment. Soil total organic carbon, total nitrogen, and total phosphorus declined with increasing fire severity. A severe burn led to a substantial reduction of soil carbon and nitrogen, which were not recovered seven years after fire. However, there was no substantial change in the C/N ratio. For the two chosen areas, soil C/N ratios decreased with depth. In the first post-fire year, total potassium content increased and were similar at the sites affected by fires of different severity in the area burned seven years ago. There was no significant change in available phosphorus and available potassium. These changes were notable in the active layer and/or organic layers, but not so in the near-surface permafrost layer. Our results suggest that, in permafrost regions, forest fires have important effects on the distribution of soil carbon and other nutrients. This study on the feedback mechanisms between forest fires and nutrients in discontinuous permafrost regions in the northern Da Xing’anling Mountains is of importance for understanding the boreal carbon pool and cycling.

Investigations of past biotic responses to rapid climate shifts are useful for developing biological scenarios that may result from future climate change. In this context, the Younger Dryas (YD) cold climatic reversal (~12,800–11,500 cal yr BP), and the resulting vegetation response, is of considerable interest. In this study, we conducted pollen and grain-size analyses of a section spanning the interval of 17,600–8500 cal yr BP in a sediment core from Xingyun Lake, in Yunnan Province, southwest China. At the same time, the other 44 paleovegetation sites from Yunnan Plateau and elsewhere in China were reviewed. Our aims were to investigate the vegetation responses to climate changes during the YD and to integrate them with climate simulation results. During the YD climatic reversal, mean annual temperatures in Yunnan were ~1.5–2.4 °C colder than today. The vegetation response to the cooling during the YD was characterized by downward shifts in the elevation of vegetation zones. Notably, only a relatively small proportion of taxa, i.e., Abies, Picea, Pinus, Quercus (E), Quercus and Poaceae, were climatically sensitive during the YD, and changes in spring temperature were a major factor on the vegetation dynamics. In addition, there was a time lag in the vegetation response to the YD event in the Yunnan Plateau. Consistent with other records from China, the YD climatic reversal only caused a change in vegetation composition rather than vegetation type succession. Notably, there was a latitudinal gradient in the magnitude of the YD cold event in China and in the resulting vegetation response. Changes in both temperature and precipitation were responsible for the vegetation changes at mid-to-high-latitudes, whereas the vegetation dynamics at low latitudes were determined largely by changes in spring temperature.

This paper examines the relationship between the extent of permafrost during the Last Permafrost Maximum (LPM, largely between 22 and 17 ka BP) and the altitudinal and latitudinal temperature gradients that controlled its extent. The region chosen, namely, the Qinghai-Tibet Plateau and the transition to the northern adjacent plains in the North China Plain, is of relatively limited extent in order to avoid regional effects. This area extends over 15 degrees of latitude while altitudes vary from 1000 to 1500 m above sealevel (asl) in the northern plains to more than 4000 m asl in the central-to-south part of the Qinghai-Tibet Plateau. The respective lowest southernmost permafrost occurrences at a northern and a southern position are used for reconstruction of the latitudinal and altitudinal gradients. As a first approximation, we conclude that the elevation compensation during the LPM for a 1° latitude change was between 309 m and 385 m. This is considerably higher than the value calculated for existing permafrost in the region that uses thermal data at a depth of zero amplitude change (139–198 m altitudinal compensation for 1° latitude).

In order to provide reliable modulus estimating equation, based on Spherical template indenter test and linear elastic theory, it obtained two different modulus formulations, called as strict solution and modified solution relatively. Following then, a general equation group was provided to illustrate the reason causing the difference of those two solutions. Using the testing data of frozen samples, the simulation was built to examine those two solutions with result that modified solution was better consistent with simulation and experimental data. Simulation results indicated that the frictionless hypothesis used for analysis was approximately correct within specific contacting area. By comparison with other experiment results, it found that the modified solution gave more safety value while the strict solution overestimated the compression modulus of frozen soil. Therefore, the modified solution is a feasible and reliable function applied for determining compression modulus of frozen soil.

Fine-scale three-dimensional (3D) permafrost distributions at the basin scale are currently lacking. They are needed to monitor climate and ecosystem change and for the maintenance of infrastructure in cold regions. This paper determined the horizontal and vertical distributions of permafrost and its quantitative responses to climate warming in the High Asia region by constructing a quasi-3D model that couples heat transfer and water movement and is forced by spatially-interpolated air temperatures using an elevation-dependent regression method. Four air temperature scenarios were considered: the present state and air temperature increases of 1, 2 and 3 °C. A fine-scale permafrost map was constructed. The map considered taliks and local factors including elevation, slope and aspect, and agreed well with field observations. Permafrost will experience severe degradation with climate warming, with decreases in area of 36% per degree increase in air temperature, increases in the depth-to-permafrost table of 2.67 m per degree increase in air temperature, and increases in 15 m-depth ground temperatures of 1.25 °C per degree increase in air temperature. Permafrost is more vulnerable in and beside river valleys than in high mountains, and on sunny rather than shady slopes. These results provide an effective reference for permafrost prediction and infrastructure and ecosystem management in cold regions affected by global warming.

The magnitude of soil and sediment erosion and accumulation processes can profoundly affect landscape development and hamper efficient management of natural resources. Consequently, estimating the rates and causes of these processes is essential, particularly in remote regions, for prediction of changes in landform and river evolution and protection of local ecosystem. We here present the results of a soil and sediment erosion investigation in the Source Area of the Yellow River (SAYR), northeast Qinghai-Tibet Plateau based on a combined analysis of

The processes of thawing and freezing and their associated complex hydrothermal coupling can significantly affect variations in mean annual temperatures and the formation of ground ice in permafrost regions. In this article, using soil temperature and moisture data in the permafrost region of the Nanweng’he River in the Da xing’anling Mountains, the freeze-thaw characteristics of the permafrost were studied. Variations in the soil temperature and the moisture were analyzed during each stage of the freeze-thaw process, and the effects of the soil moisture and ground vegetation on the freezing-thaw were discussed in this paper. The study results show that the thawing in the active layer is unidirectional, while the ground freezing is bidirectional (upward from the bottom of the active layer and downward from the ground surface). During the annual freeze-thaw cycle, the migration of soil moisture had different characteristics at different stages. In general, during of a freezing-thawing cycle, the soil water molecules will migrate downwards, i.e., soil moisture will transport from the entire active layer to the upper limit of permafrost. In the meantime, freeze-thaw in the active layer can be significantly affected by the soil moisture content and vegetation.

Application of the distributed temperature sensing (DTS) system in environmental and earth sciences is a rapidly evolving field. The aim of this review is to provide information to the novice and expert alike for the use of a DTS system for soil physical measurements. DTS is capable of measuring soil temperature at scales of meters to kilometers, and soil thermal properties and water contents can be derived based on DTS-measured temperatures. This literature review summarizes the interdisciplinary results obtained by theoretical, experimental, and numerical methods in laboratory and field investigations. This review is organized as follows: (1) review of theories and principles for Raman-DTS, the components of a DTS system, methods for measurements, calibration, data interpretation, and accuracy and precision assessment of the DTS method for soil science and hydrological application; (2) discussion of the applications of the DTS method for soil temperature, thermal properties, and water/moisture measurement; and (3) discussion of the limitations and perspectives for the application of DTS and its similarity to the heat pulse method. The chapter closes with a brief overview of future needs and opportunities for further development and application of the DTS method.