Soil Temperature Distribution Research Articles

Investigation on thermal performance of steel heat exchanger for ground source heat pump systems using full-scale experiments and numerical simulations

In this manuscript, we investigated thermal performance for a new type of ground heat exchanger (GHE) with higher thermal conductivity materials of steel by using both methods of full-scale experimental tests (pipes buried underground with a depth of 100m) and computational fluid dynamics (CFD) simulation. Thermal performance was based on the temperature differences between inlet and outlet of U-tubes and the heat transfer per unit borehole depth (QL). In addition, we also analyzed the entire thermal resistance of the borehole and the surrounding soil as well as the soil temperature distribution around the heat exchanger U-tubes. We found the further apart from the U-tubes, the smaller the soil temperature. Due to smaller heat resistance magnitude, the GHE performance of steel pipe was always better compared to conventional PE types, with QL increased up to 36%. Moreover, different inlet mass flow rates were also taken into consideration, and we found QL was always increasing with the increase of inlet velocities. The designed distance of GHE borehole was recommended to be larger than at least 1.4m for steel pipe system and 1.2m for PE one when the system is operated in continuous periods or intermittent operation of 8h. Finally, cost analysis for both steel systems and the PE ones were discussed. This study will further facilitate for the future application of steel GHE for Ground Source Heat Pump systems.

Spatial distribution of soil water, soil temperature, and plant roots in a drip-irrigated intercropping field with plastic mulch

Intercropping and drip irrigation with plastic mulch are two agricultural practices used worldwide. Coupling of these two practices may further increase crop yields and land and water use efficiencies when an optimal spatial distribution of soil water contents (SWC), soil temperatures, and plant roots is achieved. However, this coupling causes the distribution of SWCs, soil temperatures, and plant roots to be more complex than when only one of these agricultural practices are used. The objective of this study thus was to investigate the effects of different irrigation treatments on spatial distributions of SWCs, soil temperatures, and root growth in a drip-irrigated intercropping field with plastic mulch. Three field experiments with different irrigation treatments (high T1, moderate T2, and low T3) were conducted to evaluate the spatial distribution of SWCs, soil temperatures, and plant roots with respect to dripper lines and plant locations. There were significant differences (p < 0.05) in SWCs in the 0–40 cm soil layer for different irrigation treatments and between different locations. The maximum SWC was measured under the plant/mulch for the T1 treatment, while the minimum SWC was measured under the bare soil surface for the T3 treatment. This was mainly due to the location of drippers and mulch. However, no differences in SWCs were measured in the 60 100 cm soil layer. Significant differences in soil temperatures were measured in the 0 5 cm soil layer between different irrigation treatments and different locations. The soil temperature in the subsoil (15 25 cm) under mulch was higher than under the bare surface. The overlaps of two plant root systems in an intercropping field gradually increased and then decreased during the growing season. The roots in the 0 30 cm soil layer accounted for about 60% 70% of all roots. Higher irrigation rates produced higher root length and weight densities in the 0 30 cm soil layer and lower densities in the 30 100 cm soil layers. Spatial distributions of SWCs, soil temperatures, and plant roots in the intercropping field under drip irrigation were significantly influenced by irrigation treatments and plastic mulch. Collected experimental data may contribute to designing an optimal irrigation program for a drip-irrigated intercropping field with plastic mulch.

Identification of Climatic Factors Affecting the Epidemiology of Human West Nile Virus Infections in Northern Greece.

Climate can affect the geographic and seasonal patterns of vector-borne disease incidence such as West Nile Virus (WNV) infections. We explore the association between climatic factors and the occurrence of West Nile fever (WNF) or West Nile neuro-invasive disease (WNND) in humans in Northern Greece over the years 2010–2014. Time series over a period of 30 years (1979–2008) of climatic data of air temperature, relative humidity, soil temperature, volumetric soil water content, wind speed, and precipitation representing average climate were obtained utilising the ECMWF’s (European Centre for Medium-Range Weather Forecasts) Re-Analysis (ERA-Interim) system allowing for a homogeneous set of data in time and space. We analysed data of reported human cases of WNF/WNND and Culex mosquitoes in Northern Greece. Quantitative assessment resulted in identifying associations between the above climatic variables and reported human cases of WNF/WNND. A substantial fraction of the cases was linked to the upper percentiles of the distribution of air and soil temperature for the period 1979–2008 and the lower percentiles of relative humidity and soil water content. A statistically relevant relationship between the mean weekly value climatic anomalies of wind speed (negative association), relative humidity (negative association) and air temperature (positive association) over 30 years, and reported human cases of WNF/WNND during the period 2010–2014 could be shown. A negative association between the presence of WNV infected Culex mosquitoes and wind speed could be identified. The statistically significant associations could also be confirmed for the week the WNF/WNND human cases appear and when a time lag of up to three weeks was considered. Similar statistically significant associations were identified with the weekly anomalies of the maximum and minimum values of the above climatic factors. Utilising the ERA-Interim re-analysis methodology it could be shown that besides air temperature, climatic factors such as soil temperature, relative humidity, soil water content and wind speed may affect the epidemiology of WNV.

A fast distributed parameter model of ground heat exchanger based on response factor

Ground heat exchanger (GHE) is an important component of ground-coupled heat pump system. The soil temperature distribution and heat exchange capacity of GHE will largely determine the overall performance of the system. Consequently, it is very important for system design and its further performance improvement to seek a proper method of calculating the soil temperature field around GHE and the corresponding heat exchange rate. To break the limits of the existing calculating solutions and to improve the calculation accuracy and speed simultaneously, a fast distributed parameter model based on response factor (RF model) was proposed in this paper. The response factor refers to the contribution of a heat source to the excess temperature variation of a certain soil point. In a case study, the response factors and the temperature distribution of the soil heat container around one borehole were calculated using the RF model. Compared with results of numerical simulations, it can be known that the RF model equaled numerical solution in terms of accuracy, but enjoyed faster speed over numerical solution. In addition, the RF model was validated against the experiment data, with deviations less than 1.2%. In conclusion, the proposed RF model was a potential solution to predict the transient soil temperature distribution fast and accurately.

The performance analysis of a new thermal backfill material for underground power cable system

Lafarge Gruntar™ material is proposed in this paper as a new thermal backfill component, and different mass fractions such as 5%, 10%, and 15% are examined. The thermal properties of the developed backfill are determined by experiments with respect to water content and time. Based on the experimental data it is found that the 15% mass fraction Lafarge Gruntar™ material provides the most favorable thermal conductivity i.e. over 1.00W/(mK) in the dry state. This paper also presents a thermal performance optimization procedure for the high voltage underground power cable system. The new thermal backfill material is considered to be installed within the cable system to improve its thermal performance. The analyzed system consists of three underground power cables situated in a flat formation (in−line arrangement) in thermal backfill, buried in the native soil. To avoid extensive mechanical loads caused by vibrations, when locating beneath a paved ground (e.g. under road crossings), the cables are situated in High Density Polyethylene (HDPE) casing pipes filled with sand−bentonite mixture. The pipes are then placed into a thermal backfill and buried in the native soil. The Installation of thermal backfill material is relatively expensive since in many cases the buried line is installed over many kilometers. Therefore, it is important to determine the optimal dimensions of the cable bedding layer to minimize the material and installation costs while keeping efficient heat dissipation from the cables. The momentum-type Particle Swarm Optimization (PSO) solver, with a dynamic penalty function, is used to minimize the cable backfill cross-sectional area while not exceeding the allowable temperature of the cable operation. The performed optimization procedure obtains the converged solution. The temperature distribution in soil, cables, and the cable backfill layer is determined using the Finite Element Method. The Campbell − de Vries thermal conductivity model is employed for the soil surrounding the underground power cable system. An MATLAB code is written for solving the heat conduction equation and to determine the temperature distribution within the underground power cable system. By using the momentum-type Particle Swarm Optimization algorithm, it is possible to design the best-found dimensions of the cable bedding layer (width and height). Moreover, the dynamic penalty function employed in the optimization procedure has assured the determination of the maximum temperature of cable conductor close to its best-found value.

Laboratory investigations of the thermal performance of an energy pile with spiral coil ground heat exchanger

Spiral coil energy pile is a new type of ground heat exchanger (GHE) used in the ground coupled heat pump (GCHP) system. In this manuscript, a model experimental apparatus of energy pile with spiral coil was set up based on the similarity principle. The experimental investigations of influences of inlet water temperature, intermittent operation mode, spiral pitch and pile material on the thermal behavior of the spiral coil energy pile and soil temperature distribution around it were performed on the experimental apparatus. The experimental results indicate that increasing the inlet temperature contributes to the increase of heat release rate of coil, and the heat release rate increases approximately linearly with the inlet temperature. At the same time, the higher the inlet temperature, the more the heat storage in the pile. For a given inlet temperature, the soil temperature at a level gradually increases from center to outer surface of the pile, and then drops sharply across the outer surface. Under the intermittent operation mode, the soil temperature rise can be stayed effectively by a reasonable intermittent operation control, and thus the performance of GCHP can be improved. As for the spiral pitch, reducing the spiral pitch can increase the total heat release rate of the coil, but also result in the decrease of heat release rate per unit pipe length. Thus, the spiral pitch cannot be reduced unlimitedly and should be optimized through considering the total heat release rate, the heat release rate per unit pipe length, available pile area, and the costs of installation and material. Additionally, increasing the thermal effusivity of pile material can enhance the heat release rate of coil, but also reduce the temperature restoration effect of the soil surrounding the pile. Thus, the selection of pile materials should be overall considered according to the construction requirement of building foundation pile and the heat transfer optimization of energy pile.

Efficiency and economic analysis of utilizing latent heat from groundwater freezing in the context of borehole heat exchanger coupled ground source heat pump systems

To utilize the shallow geothermal energy, heat pumps are often coupled with borehole heat exchangers (BHE) to provide heating and cooling for buildings. In cold regions, soil freezing around the BHE is a potential problem which will dramatically influence the underground soil temperature distribution, subsequently the inlet and outlet circulating fluid temperature of the BHE, and finally the efficiency of the heat pump. In this study, a numerical model has been developed to simulate the coupled temperature evolution both inside the BHE, and the propagating freezing front in the surrounding soil. The coupled model was validated against analytical solutions and experimental data. The influence of the freezing process on the overall system performance is investigated by comparing one long BHE configuration without freezing and another short one with latent heat from the frozen groundwater. It is found that when freezing happens, the coefficient of performance (COP) of the heat pump will decrease by around 0.5, leading to more electricity consumption. Furthermore, analysis of the simulation result reveals that the exploitation of latent heat through groundwater freezing is only economically attractive if electricity price is low and interest rate high, and it is not the case is most European countries.

The application of energy balance at the bare soil surface to predict annual soil temperature distribution

A complex model for the prediction of annual soil temperature distribution is presented in the study. This model is based on a transient heat conduction differential equation with the energy balance at the soil surface as a boundary condition. The boundary condition involves both shortwave and longwave radiation energy, convection and latent evaporation energy, which makes the model dependent on meteorological data such as air temperature, air relative humidity, total solar radiation on a horizontal plane, wind velocity, cloud cover and snow cover. The computer program FlexPDE, based on the finite elements numerical solutions of energy flow equations, was used for simulating the soil temperature distribution inside the domain. Next, the model was validated on the basis of the measured soil temperature distribution at depths of 5cm, 50cm and 100cm. The measured and simulated values are in high agreement, as the correlation factor reaches 0.99 [-].The model is useful for the prediction of thermal performance of the building’s partitions in direct contact with soil, like that of green roofs. The model has already been used in the hybrid model for energy demand analysis of earth-sheltered buildings and may be used for buildings with green roofs.

Soil–atmosphere exchange of carbon dioxide, methane and nitrous oxide in shelterbelts compared with adjacent cropped fields

Farm shelterbelts are used as a management tool to reduce erosion, conserve moisture, protect crops and buildings, and sequester carbon. Although carbon storage in shelterbelts has been well researched, there have been no measurements of soil trace gas exchange in shelterbelts relative to cropped fields. Our objective was to quantify, for the first time, soil CO2, CH4 and N2O fluxes from shelterbelts and compare them to emissions from adjacent cropped fields to assess their potential for greenhouse gas (GHG) mitigation. During 2013 and 2014, non-steady state vented chambers were used to monitor soil GHG fluxes from nine shelterbelts and their associated cropped fields at three locations within the Boreal plains and Prairies Eco-zones of Saskatchewan Canada. Mean cumulative CO2 emissions from shelterbelt soils were significantly (P<0.0001) greater than those from cropped fields (i.e., 4.1 and 2.1Mg CO2-Cha−1yr−1, respectively). However, soil organic carbon (SOC) storage (0–30cm) was 27% greater – representing an increase of 28Mgha−1 – in the shelterbelts than in the cropped fields. Soil CH4 oxidation was greater (P<0.0001) in shelterbelts than in adjacent cropped fields (i.e., −0.66 and −0.19kgCH4-Cha−1yr−1, respectively) and cropped soils emitted significantly (P<0.0001) greater quantities of N2O than the shelterbelts (i.e., 2.5 and 0.65kgN2O-Nha−1yr−1, respectively). Total seasonal exchange of non-CO2 GHGs was reduced by 0.55MgCO2eha−1yr−1 in shelterbelts as compared with cropped fields, 98% of which was soil-derived N2O. Patterns of soil temperature, moisture and organic matter distribution beneath shelterbelts suggest a modification in soil micro-environment due to shelterbelt establishment and root activity that, in turn, may be responsible for the observed increase in soil CO2 emissions and CH4 oxidation. Our data demonstrate that shelterbelts have substantial potential to mitigate GHGs by enhancing C storage and reducing N2O emissions, while maintaining a strong CH4 sink.

Diffuse carbon dioxide emissions from hidden subsurface structures at Asama volcano, Japan

We measured diffuse carbon dioxide (CO2) flux and soil temperature around the summit of Asama volcano, Japan to assess the diffuse degassing structure around the summit area. Soil CO2 flux was measured using an accumulation chamber method, and the spatial distributions of CO2 flux and soil temperature were derived from the mean of 100 sequential Gaussian simulations. Results show that soil CO2 flux was high on the eastern flank of Kamayama cone and the eastern rim of Maekake crater, the outer cone. These areas mostly correspond to high-temperature anomalies. The average emission rate of diffuse CO2 was calculated to be 12.6 t day−1 (12.2–14.6 t day−1). Such diffuse emissions account for 12 % of the total (diffuse and plume) CO2 emissions from the summit area. The diffuse CO2 anomalies probably reflect permeable zones controlled by local topography and hidden fractures bordering Maekake crater. The permeable zones are connected to the low-electrical-resistivity zone inferred to indicate both a hydrothermal fluid layer and an upper sealed layer made of clay minerals. Magmatic gas from the main conduit ascends to the volcano surface through this fluid layer and the permeable zones. These insights emphasize that the pathways and the connection between the pathways and the source of diffuse CO2 combine to create the pattern of heterogeneous diffuse CO2 emission seen at the surface. Only by using a combination of gas measurements and geophysical tools can we begin to understand the dynamics of this system as a whole.

Effect of the choice of boundary conditions on modelling ambient to soil heat transfer near a buried pipeline

The soil temperature distribution influences the thermal interaction between the ambient and subsurface objects. This paper shows the effect of the soil surface boundary conditions on heat transfer calculations around a buried pipeline. The results are compared to measurements from an experimental installation. Measurements include soil temperatures, the soil surface radiation balance, and weather parameters. The heat conduction problem is modelled with one- and two-dimensional models. The models were used to find the sensitivity for different soil surface boundary condition assumptions. The results are compared to the measured soil thermal profiles and the pipeline to ambient heat transfer. Using both the measured soil surface temperature and the full surface energy balance provides similar and accurate soil temperature prediction. A reduction in predictive accuracy of soil temperatures occurs when using measured air temperatures for the soil surface boundary condition This has an effect on the long term pipeline to ambient heat transfer.

Analysis of underground cable ampacity considering non-uniform soil temperature distributions

An analytical model for the assessment of cable ampacity due to non-uniform underground temperature distribution is presented. The uneven underground temperature is usually caused by a non-uniform surface heating (e.g., a street or parking crossing, etc.), which is extended for certain length along the cable installation and in depth. The underground temperature distribution is obtained by solving the heat equation with the respective boundary conditions. The cable ampacity reduction is calculated as a function of the surface temperature distribution and the cable depth of burial. The model is validated and several numerical results are obtained for different installation conditions.

A continuous dynamic feature of the distribution of soil temperature and horizontal heat flux next to external walls in different orientations of construction sites in the autumn of Beijing, China

Soil is an important carrier of the urban ecosystem. Many eco-systematic processes take place in the soil surface layer and are controlled directly by soil temperature. However, accelerated global urbanization and urban construction lead to urban heat islands, causing higher air temperatures in urban areas than those in rural areas. For the same reason, soil temperature is higher in urban areas. Higher soil temperatures may cause changes in eco-systematic processes. Therefore, studying and understanding how soil temperature changes in urban areas is necessary. In other words, the heat impact from urban construction, including its process and extent, on soil needs further researches. In this study, the experimental transect was arranged in the ecotone between construction and green space. The temperature of the surface soil layer was investigated and recorded to analyze urban construction horizontal heat impact process and quantity on the soil of green space in urban areas during autumn within Beijing city, China. Several acquired results are as follows: in autumn, downward-trend distributions of soil temperature were found along the construction-soil micro gradient transect next to the south, north, east and west side external walls. The south, north, east and west side external walls' maximum horizontal heat impact scopes are 0.15, 0.0167, 0.1 and 0.05 m, respectively, on a diurnal scale. The daily horizontal heat impact process was different along the experimental transect, changing with orientation of the building external wall. According to continuous investigation, a formulation of horizontal heat flux (Gh, between buildings and soil) and ΔT (difference between soil temperature 0 and 0.05 m from the building baseline) was generated: Gh = 31.77ΔT + 8.11 (P < 0.0001), where R2 was 0.976. In addition, no significant difference (P > 0.05) was found between the value of simulation and measurement via a two-tailed T test. Based on this formulation, a continuous dynamic-feature for heat flux was calculated. On a diurnal scale, the mean horizontal heat flux at different orientations of external walls for both sunny and cloudy days are as follows: 44.13 and 7.07 W/m2 for south, 28.15 and 9.22 W/m2 for north, 21.44 and 9.66 W/m2 for east and 24.42 and 13.54 W/m2 for west. Downward gradient distributions of mean horizontal heat flux of autumn were calculated; for south, north, east and west side external walls, the maximum was 29.94, 25.44, 24.87 and 23.50 W/m2 and the minimum was 7.31, 6.46, 7.45 and 4.81 W/m2. Therefore, construction sites were considered to be a heat source for soil and provided soil with thermal energy, leading to a higher soil temperature around construction sites in urban areas during autumn. This study focused on urban construction horizontal heat impacts on the soil of adjacent green space in conditions of different weather in autumn and helped us to understand the quantitative processes of horizontal heat impact. In addition, the study will benefit research examining the ecological relationships of urban heat islands and ecosystem processes.

Fem-Based Thermal Analysis of Underground Power Cables Located in Backfills Made of Different Materials

This paper presents the preliminary thermal analysis of the underground transmission line, which will be applied in the Polish power plant that produces 600 MW of power. The paper considers a system of three power cables located in the in-line arrangement placed in the HDPE casing pipes buried in the multilayered soil (the native soil and the thermal backfill). Different configurations of bedding layers are analyzed. The burial depth of the cables, measured from the reference level (0.5 m below the ground) varies from 2 to 6 m. What influences the temperature distribution in soil, cable bedding and cable conductor. The numerical computations of the steady-state temperature fields are performed using the finite element method. Additionally, to include the dry-zone formation effect on the temperature distribution, the soil thermal conductivity is considered to be temperature-dependent.

Comparative Study on Heat and Moisture Transfer in Soil Heat Charging at High Temperature for Various Soils

To investigate the mechanism of heat and moisture transfer in soil heat charging for solar-soil source heat pump system, a testing rig of one-dimension soil heat charging is constructed. Two different soils, sand and loam, are used for the testing. The soil temperature distribution and volumetric water content (VWC) variations are studied under different heat source temperature and soil initial VWC, and the difference between these two soils is analysed as well. The coupled and mutual effect of heat and moisture transfer is discussed. The study shows that sand is better than loam in soil heat charging. The heat source temperature has an obvious impact on soil VWC distribution. Higher heat source temperature leads to higher peak VWC. The initial VWC has a slight impact on soil temperature distribution.

Restoration performance of vertical ground heat exchanger with various intermittent ratios

Based on five intermittent operation modes with the intermittent ratios of 0.7, 1, 1.4, 2 and 3, the effect of intermittent operation on restoration performance of vertical ground heat exchanger in Ground Source Heat Pump was investigated in terms of heat exchange flux, temperature difference, soil temperature distribution and thermal radius. Meanwhile, a heat transfer model of the GHE has been developed by combining the analytical solution and numerical solution, whose calculation area has been divided into two parts by the boundary of the borehole wall. For the area in the borehole, the calculation method is steady analytical solution based on energy conservation, whereas for the soil area, the finite volume method is adopted, and the two parts are coupled by the temperature and heat flux of the borehole. The simulation results indicate that intermittence operation modes can improve the heat exchange performance of ground heat exchanger. Furthermore, when the intermittent ratio is 3, the restoration performance is the best due to the longest stopping time. With the operation proceeding, the enhancement of the heat flux arising from the intermittence becomes more obvious while the restoration ratio of average temperature of borehole decreases simultaneously.

Modeling the interactions between the performance of ground source heat pumps and soil temperature variations

The adoption of geothermal energy in space conditioning of buildings through utilizing ground source heat pump (GSHP, also known as geothermal heat pump) has increased rapidly during the past several decades. However, one problem in operating GSHPs is that collection or rejection heat from the ground alters the ground temperature, which can adversely affect the coefficient of performance (COP). In turn, the amount of heat that must be exchanged with the ground increases in order to satisfy a given heating or cooling load. This paper presents a novel model to calculate the soil temperature distribution and the COP of GSHP. Different scenarios were simulated to quantify the impact of different factors on the GSHP performance, including seasonal balance between heat collection and heat rejection, daily running mode, and spacing between boreholes. Our results show that greater loads and smaller distances between boreholes cause changes in soil temperature large enough to adversely affect the GSHP performance, even resulting in COPs less than those commonly achieved with air source heat pumps. However, shifting from heating to cooling on a seasonal basis can, in part, mitigate this problem. Long boreholes, additional space between boreholes and intermittent running mode could also improve the performance of GSHP, but large initial investment is required.

Factors controlling soil organic carbon persistence along an eroding hillslope on the loess belt

The integration of hydrologic, geomorphic and biogeochemical approaches is required to determine organic carbon (OC) persistence and dynamics within landscapes. Here, we studied the persistence of OC along an eroding hillslope using soil in situ surface heterotrophic respiration measurement as an indicator. Along this topographical gradient, we quantified the space-time distribution of soil water and temperature as well as the amount of labile OC (i.e. NaOCl-non-resistant) in relation to CO2 fluxes. We used a Generalized Least Square (GLS) regression model (i) to identify the role of each abiotic factor as well as their interactions, and (ii) to quantify spatial differences in CO2 fluxes along the hillslope.We observed significant differences in respiration along the topographical gradient, i.e. 30% more at the downslope and 50% more at the backslope, relative to the uneroded summit position. Soil OC persistence along the hillslope was mainly controlled by the labile OC stock and moisture content. Our in-situ measurements also indicated that the temperature sensitivity of soil OC (as expressed by Q10 values) was strongly related to soil water content. The large stock of OC stored in colluvial soils has a higher temperature sensitivity (Q10 = 3.72 ± 0.17) than in non-depositional slope positions (Q10 = 1.77 ± 0.18 to 2.59 ± 0.13). Given the large stock of labile OC, its high temperature sensitivity and the high water contents that are needed to stabilize OC, we conclude that the OC stored in colluvial soils is particularly vulnerable to OC mineralization under drier/warmer conditions. When considering the large amount of OC that has been buried globally as a result of agricultural erosion during the last decades, the long-term stability of this pool under future land use and/or climate disturbance is an area of concern.

Distribution and changes of active layer thickness (ALT) and soil temperature (TTOP) in the source area of the Yellow River using the GIPL model

Active layer thickness (ALT) is critical to the understanding of the surface energy balance, hydrological cycles, plant growth, and cold region engineering projects in permafrost regions. The temperature at the bottom of the active layer, a boundary layer between the equilibrium thermal state (in permafrost below) and transient thermal state (in the atmosphere and surface canopies above), is an important parameter to reflect the existence and thermal stability of permafrost. In this study, the Geophysical Institute Permafrost Model (GIPL) was used to model the spatial distribution of and changes in ALT and soil temperature in the Source Area of the Yellow River (SAYR), where continuous, discontinuous, and sporadic permafrost coexists with seasonally frozen ground. Monthly air temperatures downscaled from the CRU TS3.0 datasets, monthly snow depth derived from the passive microwave remote-sensing data SMMR and SSM/I, and vegetation patterns and soil properties at scale of 1:1000000 were used as input data after modified with GIS techniques. The model validation was carried out carefully with ALT in the SAYR has significantly increased from 1.8 m in 1980 to 2.4 m in 2006 at an average rate of 2.2 cm yr−1. The mean annual temperature at the bottom of the active layer, or temperature at the top of permafrost (TTOP) rose substantially from −1.1°C in 1980 to −0.6°C in 2006 at an average rate of 0.018°C yr−1. The increasing rate of the ALT and TTOP has accelerated since 2000. Regional warming and degradation of permafrost has also occurred, and the changes in the areal extent of regions with a sub-zero TTOP shrank from 2.4×104 to 2.2×104 km2 at an average rate of 74 km2 yr−1. Changes of ALT and temperature have adversely affected the environmental stability in the SAYR.

A simple framework to estimate distributed soil temperature from discrete air temperature measurements in data‐scarce regions

AbstractSoil temperature is a key control on belowground chemical and biological processes. Typically, models of soil temperature are developed and validated for large geographic regions. However, modeling frameworks intended for higher spatial resolutions (much finer than 1 km2) are lacking across areas of complex topography. Here we propose a simple modeling framework for predicting distributed soil temperature at high temporal (i.e., 1 h steps) and spatial (i.e., 5 × 5 m) resolutions in mountainous terrain, based on a few discrete air temperature measurements. In this context, two steps were necessary to estimate the soil temperature. First, we applied the potential temperature equation to generate the air temperature distribution from a 5 m digital elevation model and Inverse Distance Weighting interpolation. Second, we applied a hybrid model to estimate the distribution of soil temperature based on the generated air temperature surfaces. Our results show that this approach simulated the spatial distribution of soil temperature well, with a root‐mean‐square error ranging from ~2.1 to 2.9°C. Furthermore, our approach predicted the daily and monthly variability of soil temperature well. The proposed framework can be applied to estimate the spatial variability of soil temperature in mountainous regions where direct observations are scarce.