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Abstract The permafrost in the Da Xing'anling Mountains Northeastern China has experienced rapid and significant degradation due to climate warming and human activities during the last few decades. In this study, the permafrost degradation and freezing/thawing characteristics of the active layer at Mo'he airport were investigated through a ground temperatures data set collected over 10 years of measurements. During the monitoring period, thawing permafrost under the airport was observed, induced by climate warming, and thermal disturbance of airport construction and operation. The permafrost table under the blast pad declined considerably and varied from −9 m to −14 m, and from −4.5 m to −12 m under the natural site. The maximum depth of frost penetration at this airport shows a decreasing trend. The freezing duration of soil under the blast pad is shorter comparing with the natural ground surface, while its thawing duration is longer. The warming rates of permafrost at −10 m depth under the blast pad were 0.25–0.33 °C/a, and those under the natural ground were 0.03 °C/a and 0.15 °C/a. The results provide valuable data for designing, construction and operation of the airport, and a reference for other airports construction in permafrost regions. Highlights • The permafrost under the Mo'he airport degraded and disappeared during the past 10 years. • The maximum depths of frost penetration under the runway exhibited a decreasing trend. • The freezing duration of foundation soil under the concrete blast pad was shorter and its thawing duration was longer. • The deep ground temperature under the blast pad showed a higher warming rate. [ABSTRACT FROM AUTHOR]

Knowledge of the spatial distribution of permafrost and the effects of climate on ground temperature are important for land use and infrastructure development on the Qinghai-Tibet Plateau (QTP). Different permafrost models have been developed to simulate the ground temperature and active layer thickness (ALT). In this study, Temperature at Top of Permafrost (TTOP) model, Kudryavtsev model and modified Stefan solution were evaluated against detailed field measurements at four distinct field sites in the Wudaoliang Basin to better understand the applicability of permafrost models. Field data from 2012 to 2014 showed that there were notable differences in observed ground temperatures and ALTs within and among the sites. The TTOP model is relatively simple, however, when driven by averaged input values, it produced more accurate permafrost surface temperature (Tps) than the Kudryavtsev model. The modified Stefan solution resulted in a satisfactory accuracy of 90%, which was better than the Kudryavtsev model for estimating ALTs. The modified Stefan solution had the potential of being applied to climate-change studies in the future. Furthermore, additional field investigations over longer periods focusing on hydrology, which has significant influence on permafrost thaw, are necessary. These efforts should employ advanced measurement techniques to obtain adequate and extensive local parameters that will help improve model accuracy. [ABSTRACT FROM AUTHOR]

• Forest fire has evident influences on hydrothermal regimes of permafrost. • Fire-induced hydrothermal changes tend to enlarge with increasing fire severity. • Changes in hydrothermal regimes are evident in near-surface permafrost after fires. • The freeze–thaw processes after fire differ evidently from those of unburned sites. Forest fires potentially result in the irreversible and rapid degradation of permafrost, soil evolution, successions of boreal forests, and consequent development of hazardous periglacial landforms. Two burned-areas of Mangui and Alongshan at the western flank of the northern Da Xing'anling Mountains in Northeast China were chosen to study the effects of forest fires on thermal regimes of near-surface permafrost and the active layer. The study results show risen post-fire ground temperatures with increasing fire severity, and mainly at depths of 0–1.5 m. Moreover, nine years after a severe burn, the depth of evident temperature changes exceeded 6 m, and a warming of 2.7 °C at 6 m depth was inferred. Presumably due to the influences of forest fires, the active layer thickness at severely burned sites was 3.8 m compared to 1.2 m at the un-burned site. Soil moisture content and organic-layer and snow-cover thicknesses also play important roles in further complicating the fire impacts on the permafrost environment. These impacting mechanisms and thresholds await more systematic, in-depth, and quantitative studies. Numerical models deem necessary for simulating and predicting the spatiotemporal variations in ground hydrothermal regimes under different fire severity and for evaluating the contributions and thresholds of changes in these important environmental factors (e.g., organic layer and snow cover) for the hydrothermal state of near-surface permafrost and active layer. [ABSTRACT FROM AUTHOR]

Abstract: The rising air temperature and increased human activities have caused permafrost degradation over the Qinghai–Tibet Plateau, including thickening of the active layer. The active layer plays an important role in cold regions. Active layer thickness (hereafter ALT) variation may have profound socio-economic and eco-environmental consequences. Using a climate-driven model based on Kudryavtsev''s formulations and data from climate records, snow and vegetation parameters, and soil features, we calculated ALTs of the permafrost regions over the Qinghai–Tibet Plateau. A general agreement was found when comparing the calculated results with measured values at survey sites. A distribution map of ALT over the Qinghai–Tibet Plateau shows that ALTs in the central part of the plateau are generally smaller than those in other regions while ALTs in the northern and western regions are larger than those in the eastern and southern regions of the plateau. ALTs of the permafrost regions along the Qinghai–Tibet Highway are generally larger than 2.0 m. The regions with ALTs less than 2.0 m are mainly in the high-mountain areas. [Copyright &y& Elsevier]

We established vegetation indicators of active layer thickness for the southern permafrost region in China, which can be used for monitoring permafrost degradation. • Plant community features are linked to near-surface permafrost presence in NE China. • Two Carex species and Betula fruticosa indicate near-surface permafrost explicitly. • Moss thickness and shrub cover correlate with active layer thickness of permafrost. • We established near-surface permafrost prediction models with above features. The most dramatic permafrost degradation is expected to occur at the southern edge of permafrost distribution, which is difficult to detect directly on a large scale. Ecological indicators can be used to provide an early signal of changes in terrestrial ecosystems for regional near-surface permafrost habitats and potentially to monitor near-surface permafrost degradation. In this study, plant composition and community structure indicate the near-surface permafrost distribution at the southern edge of the boreal forest and permafrost in northeastern China. The plant species composition and structure of aboveground vegetation were linked to the belowground near-surface permafrost distribution in order to find indicators of changes in vegetation features from permafrost melting. These indicators are essential for assessing changes in permafrost vegetation systems under climate change. Carex schmidtii and C. appendiculata in the herb layer and Betula fruticosa in the shrub layer were found to be specific near-surface permafrost plant indicator species, especially for the wetland permafrost. Shrub cover, moss mat thickness and tree canopy cover are also strongly correlated with near-surface permafrost distribution. The active layer thickness (ALT) showed negative correlations with moss thickness and shrub cover because these features may act as buffers for regional climate warming. We chose the cover of each indicator species, near-surface permafrost-specific community features and geographical information as independent variables to predict the possible distribution of near-surface permafrost in our study region using logistic regression. The results showed that the prediction model had good performance and accuracy. Our study sheds light on early caution of deepening of regional-scale permafrost active layer with vegetation indicators that can further be identified from satellite images. [ABSTRACT FROM AUTHOR]