Surface freezing and thawing processes pose significant influences on surface water and energy balances, which, in turn, affect vegetation growth, soil moisture, carbon cycling, and terrestrial ecosystems. At present, the changes in surface freezing and thawing states are hotspots of ecological research, but the variations of surface frozen days (SFDs) are less studied, especially in the permafrost areas covered with boreal forest, and the influence of the environmental factors on the SFDs is not clear. Utilizing the Advanced Microwave Scanning Radiometer for EOS (AMSRE) and Microwave Scanning Radiometer 2 (AMSR2) brightness temperature data, this study applies the Freeze-Thaw Discriminant Function Algorithm (DFA) to explore the spatiotemporal variability features of SFDs in the Northeast China Permafrost Zone (NCPZ) and the relationship between the permafrost distribution and the spatial variability characteristics of SFDs; additionally, the Optimal Parameters-based Geographical Detector is employed to determine the factors that affect SFDs. The results showed that the SFDs in the NCPZ decreased with a rate of -0.43 d/a from 2002 to 2021 and significantly decreased on the eastern and western slopes of the Greater Khingan Mountains. Meanwhile, the degree of spatial fluctuation of SFDs increased gradually with a decreasing continuity of permafrost. Snow cover and air temperature were the two most important factors influencing SFD variability in the NCPZ, accounting for 83.9% and 74.8% of the spatial variation, respectively, and SFDs increased gradually with increasing snow cover and decreasing air temperature. The strongest explanatory power of SFD spatial variability was found to be the combination of air temperature and precipitation, which had a coefficient of 94.2%. Moreover, the combination of any two environmental factors increased this power. The findings of this study can be used to design ecological environmental conservation and engineer construction policies in high-latitude permafrost zones with forest cover.

Satellite data on methane concentration in the lower troposphere and the dynamical permafrost model are used to analyze methane emissions in the permafrost zone. The sources of methane generation in different biochemical conditions in the river valleys, thermokarst lakes, wetlands, and lowlands are studied. The statistical relationships between their intensity and air temperature, precipitation, active layer thickness, and permafrost temperature are evaluated. The CMIP5 ensemble climate projection is used to estimate methane emission in the permafrost regions for the mid-21st century. Numerical experiments with the INM-CM48 Earth system model demonstrated that the projected 20 Tg/year increase in the methane emission will lead to less than 0.05 degrees C global temperature rise. The uncertainty analysis of the results is accomplished and an alternative conceptual model of abrupt threshold changes in methane emission is proposed.

Long-term thermal effects of air convection embankments (ACEs) over 550-km-long permafrost zones along the Qinghai-Tibet railway were analyzed on the basis of 14-year records (2002-2016) of ground temperature. The results showed that, after embankment construction, permafrost tables beneath the ACEs moved upward quickly in the first 3years and then remained stable over the next 10years. The magnitude of this upward movement showed a positive correlation with embankment thickness. Shallow permafrost temperature beneath the ACEs decreased over a 5-year period after embankment construction in cold permafrost zones, but increased sharply concurrent with permafrost table upward movement in warm permafrost zones. Deep permafrost beneath all the ACEs showed a slow warming trend due to climate warming. Overall, the thermal effects of ACEs significantly uplifted underlying permafrost tables after embankment construction and then maintained them well in a warming climate. The different thermal effects of ACEs in cold and warm permafrost zones related to the working principle of the ACEs and natural ground thermal regime in the two zones. (c) 2018 American Society of Civil Engineers.

The characteristics of temperature dynamics in a solonetzic meadow-chernozemic soil of alas depression in Central Yakutia are described on the basis of long-term (2005-2014) stationary studies. Quick changes in weather conditions accompanied by changes in the soil temperature regime were observed during that period. Thus, the beginning of soil thawing in the spring shifted to earlier dates, and the beginning of soil freezing in the fall shifted to later dates. Temperature trends demonstrate an increase in the mean annual soil temperatures at all the depths. In total, the period of the frozen state of the soil became considerably shorter: in the middle-profile horizons, by 30-39 days. The obtained results attest to the high dynamism in temperature parameters of meadow soils in alas depressions of Central Yakutia under conditions of global climate changes.