Diversity of Remote Sensing-Based Variable Inputs Improves the Estimation of Seasonal Maximum Freezing Depth

The maximum soil freezing depth (MSFD) is an important indicator of the thermal state of seasonally frozen ground. Its variation has important implications for the water cycle, ecological processes, climate and engineering stability. This study tested three aspects of data-driven predictions of MSFD in the Qinghai-Tibet Plateau (QTP), including comparison of three popular statistical/machine learning techniques, differences between remote sensing variables and reanalysis data as input conditions, and transportability of the model built by reanalysis data. The results show that support vector regression (SVR) performs better than random forest (RF), k-nearest neighbor (KNN) and the ensemble mean of the three models. Compared with the climate predictors, the remote sensing predictors are helpful for improving the simulation accuracy of the MSFD at both decadal and annual scales (at the annual and decadal scales, the root mean square error (RMSE) is reduced by 2.84 and 1.99 cm, respectively). The SVR model with climate predictor calibration using the in situ MSFD at the baseline period (2001–2010) can be used to simulate the MSFD over historical periods (1981–1990 and 1991–2000). This result indicates the good transferability of the well-trained machine learning model and its availability to simulate the MSFD of the past and the future when remote sensing predictors are not available.

Dynamics of changes in thawing and freezing depth in soils of Western Transbaikalia in different types of permafrost distribution

This study reveals temperature regimes of the three contrasting ecosystems in the permafrost area of Western Transbaikalia: meadow-forest ecosystem, forest-steppe and dry-steppe. Annual profile temperature data show the functioning of the studied soils in cryogenic and long-term-seasonally-freezing temperature regime. The most explanatory temperature variables are temperature penetration above 5°C at 100 cm depth and the amount of days with temperature above 0.5°C and 10°C at 20 cm, 50 cm, and 100 cm depths. Also, this work presents a comparative analysis of indicators of soil climate change and shows the spatial-temporal distribution of the reaction of the thawing and freezing depth in soils.

Using of the Tape Extensometer for Possibilities of Landslide Monitoring or another purposes

The main goal of this article is to analyze the possibility of using tape extensometry. It is one of the methods of evaluating the development of slope deformation. Tape extensometry is used to monitor the movement of the slope on the surface. Tape extensometry is used for fast and accurate measurement of relative distances between pairs of reference points on the surface of structures, including radial movements and convergence of tunnels, linings, shafts and caves. Then deformations of excavations in underground caves and displacements of retaining walls, bridge piers and arches. The digital tape extensometer is a portable device used to measure the displacement between pairs of eye bolts. The principle of measuring on a slope consists in directly measuring the distance between the stabilized measuring points. The measuring points are located in both stable and unstable parts. The measuring points are concreted into boreholes drilled to a non-freezing depth, which in the Czech Republic is about 0.8 m below the ground. The direction of movement can be determined by measuring the change in distance between several points located in the stable part and points in the unstable part. If we also measure in time intervals, we can also find out the approximate speed of movement. The tape extensometry method is performed using a tape extensometer. It is a specially adapted zone in which emphasis is placed on the material from which the meter is made, because it is important that the material has a low thermal expansion, for example nickel steel is suitable.

Probabilistic Analysis as a Method for Ground Freezing Depth Estimation

Accurate frost depth prediction is an important aspect in different engineering designs such as for pavements, buildings, bridge foundations, and utility lines. This paper presents a probabilistic method of assessment of the depth of soil freezing. Annual (winter) maxima of the position of the zero centigrade temperature measured in the soil were approximated by Gumbel probability distribution. Its parameters were estimated using maximum likelihood method. The results received on the basis of data from 36 meteorological stations in Poland and 50 years of observations, as characteristic values with 50-year return period, reflect the influence of the climatic conditions on the freezing depth. On the other hand, the soil structure and its conditions also play an important role in freezing. Nowadays they may be taken into account using correction coefficients. It is concluded that this method is more precise than a method using the air freezing index because through the use of direct measurements it takes into account additional factors affecting the actual depth of freezing. The obtained results are not the same as those given in the older Polish Standard which was based on the simplified and limited data. The results confirm the impact of climate change on ground freezing depth.

Influence of snow cover and air temperature on variations of ground freezing depth in Moscow and the Moscow region

<p>According to consdidered influence of snow cover thickness and air temperature on variations of ground freezing depth at the site of meteorological observatory of Moscow State University and also according to the data of observatories in the Moscow region it is expected to make conclusions about the impact of the urban heat island to a ground freezing depth in Moscow region. For this purpose, the values of the maximum ground freezing depth were analyzed for MSU meteorological observatory and for the weather stations of the Moscow region: Kolomna, Mozhaisk and Sukhinichi. And since not always the data of actual observations are avaliable, for these weather stations the calculated values of the maximum ground freezing depth were obtained. The calculations were performed according to the previously developed calculation scheme, based on the problem of thermal conductivity of a three-layer medium (snow, frozen and thawed ground) with a phase transition at the boundary. The heat balance equation included the energy of the phase transition, the inflow of heat from the thawed ground and the outflow to the frozen ground and, in the presence of snow cover, through it to the atmosphere. The heat flow was calculated according to Fourier's law as the product of the thermal conductivity and the temperature gradient. It was assumed that the temperature in each medium varies linearly. For snow cover and frozen ground, the formula of thermal conductivity of a two-layer medium was used. The obtained calculated values were compared with the actual values of the ground freezing depth. The coefficients R<sup>2</sup> of the reliability of the linear trend line approximation when comparing the calculated and actual values for Moscow and the Moscow region were at the level of 0.6-0.7. The maximum ground freezing depth in Moscow and in the Moscow region in the same years may differ by an average of 10 cm. This confirms that the designed scheme well describes ground freezing depth based on data on air temperature and snow cover thickness and can be used to model the underground heat island of the Moscow region. In report it is also supposed to present the results of the recent years observations of snow cover and freezing depth variations in Moscow and the Moscow region. The past  2020 year is considered as the warmest in the entire history of observations according to the MSU Meteorological Observatory for Moscow, according to the Hydrometeorological Center of Russia for the whole of Russia and according to the Copernicus Climate Change Service (C3S) for the entire Globe. So the winter season of 2019/20 in Moscow region was also unusually warm, and therefore in the winter season of 2019/20 there was very little snow in the Moscow region. However, the warm summer of 2020 resulted in one of the lowest summer values of sea ice extent in the Arctic and, as a result, abnormally strong minimum temperatures and heavy snowfall in the winter of 2020/21 in Eurasia and Moscow. The work was done in a frame of state topic AAAA-A16-116032810093-2.</p>

Change in climatic characteristics of the cold period of the hydrological year in the south-east of Western Siberia

This article is about the changes in climatic characteristics during the cold period of the hydrological year in the southeast of Western Siberia over the past 60 years and their impact on the depth of soil freezing in dissected territories. It has been established that at the regional level over the past 60 years there has been an increase in air temperature and an increase in precipitation during cold periods of hydrological years. These changes have a direct impact on the depth of freezing of soils in the dismembered territories of the southeast of Western Siberia. A stable tendency towards a decrease in the freezing depth was noted from 1968 to 2020.

Calculation scheme of ground freezing depth in Terskol

During the construction of avalanche-retaining geotechnical structures in mountainous areas comes up the problem of fixing and stability of these structures in conditions of seasonal and/or long-term freezing of the ground. This paper evaluates the influence of snow cover and air temperature on the depth of freezing and soil stability based on the developed calculation scheme for the winter seasons 2015/16-2019/20 in the Elbrus region. The calculation scheme was based on the problem of thermal conductivity of a three-layer medium (snow, frozen, and thawed soil) with a phase transition at the boundary. The heat balance equation included the energy of the phase transition, the inflow of heat from the thawed ground and the outflow to the frozen ground, and, in the presence of snow cover, through it to the atmosphere.

The Modelling of Freezing Process in Saturated Soil Based on the Thermal-Hydro-Mechanical Multi-Physics Field Coupling Theory

The freezing process of saturated soil is studied under the condition of water replenishment. The process of soil freezing was simulated based on the theory of the energy and mass conservation equations and the equation of mechanical equilibrium. The accuracy of the model was verified by comparison with the experimental results of soil freezing. One-side freezing of a saturated 10-cm-high soil column in an open system with different parameters was simulated, and the effects of the initial void ratio, hydraulic conductivity, and thermal conductivity of soil particles on soil frost heave, freezing depth, and ice lenses distribution during soil freezing were explored. During the freezing process, water migrates from the warm end to the frozen fringe under the actions of the temperature gradient and pore pressure. During the initial period of freezing, the frozen front quickly moves downward, the freezing depth is about 5 cm after freezing for 30 h, and the final freezing depth remains about 6 cm. The freezing depth of the soil column is affected by soil porosity and thermal conductivity, but the final freezing depth mainly depends on the temperatures of the top and lower surfaces. The frost heave is mainly related to the amount of water migration. The relationship between the amount of frost heave and the hydraulic conductivity is positively correlated, and the thickness of the stable ice lens is greatly affected by the hydraulic conductivity. With the increase of the hydraulic conductivity and initial void ratio, the formation of ice lenses in the soil become easier. With the increase of the initial void ratio and thermal conductivity of soil particles, the frost heave of the soil column also increases. With high-thermal-conductivity soil, the formation of ice lenses become difficult.

Observational variations in the seasonal freezing depth across China during 1965-2013

Long-term changes in the soil freezing-thawing depth are an important indicator of climate change. Based on data from 764 meteorological stations across China, we analysed the climatology and variability in the seasonal freezing depth (SFD) during 1965-2013 and investigated the connections among changes in the SFD, meteorological factors (temperature, precipitation, snow depth, freezing index and thawing index) and atmospheric circulations (East Asian winter monsoon [EAWM] and North Atlantic Oscillation [NAO]) in each of 4 sub-regions: northwestern China (W), the Tibetan Plateau (TP) and eastern China (E1 and E2). In addition, the contributions of 2 different factors to variation in the SFD were quantified. The results revealed that during 1965-2013, the SFD noticeably changed from positive to negative anomalies in approximately 1988 for all of the studied regions, exhibiting a significant decreasing trend at rates (mean ± SE) of 0.23 ± 0.03, 0.08 ± 0.01, 0.26 ± 0.03 and 0.24 ± 0.03 cm yr-1 in E1, E2, W and TP, respectively. The air freezing index was strongly correlated with the SFD in the E2 and TP regions, and accounted for 82.6 and 84.9% of the change in SFD, respectively. Snow depth showed a significant association with the variability in SFD only in the E1 region. Compared to the NAO, the EAWM plays an important role in changes in SFD. These findings have implications for further understanding the mechanisms of cold environment changes across China.

Verification of temperature and humidity conditions of mineral soils in the active layer model

<p>Detailed monitoring of the temperature of the soil layer provides a unique experimental material for studying the complex processes of heat transfer from the surface layer of the atmosphere to soils. According to the data of autonomous devices of air temperature, it was found that within each key area there are no significant differences between the observation sits. According to the annual (2011-2018) observations of the temperature regime of the soil and ground, it has been found that the microclimatic specificity of bog ecosystems is clearly manifested in the characteristics of the daily and annual variations in soil temperature. A regression model describing the change in the maximum freezing depth during the winter has been proposed, using air temperature, snow depth and bog water level as predictors. The effects of BWL and snow cover have similar values, which indicates an approximately equal contribution of BWL variations and snow depth to changes in freezing. The thickness of the seasonally frozen layer at all sites is 20-60 cm and the maximum freezing of the peat layer is reached in February-March. Degradation of the seasonally frozen layer occurs both from above and below.</p><p>It was found that similar bog ecosystems in different bog massifs have significantly different temperature regimes. The peat stratum of northern bogs can be both warmer (in winter) and colder (in summer) in comparison with bogs, located 520 km to the south and 860 km to the west.</p>