Ground Surface Temperature Variations Research Articles

Spatiotemporal variations and its driving factors of ground surface temperature in China

The ground surface temperature (GST) serves as a crucial indicator for understanding land-atmosphere mass and energy exchange. The shift from manual measurement to automated station for GST in China after 2002 introduced inconsistencies at certain stations, potentially distorting research findings. Here, daily automatedly observed GST from 2003 to 2017 at 615 selected meteorological stations were updated by constructing linear regression model based on manually observed air temperature (AT) and GST from 1960 to 2002. Then, the spatiotemporal variations of GST from 1960 to 2017 and its driving factors were investigated. Results indicated that: (1) the AT-GST linear regression model could effectively mitigate the inconsistency caused by the change of GST observation methods, enhancing data reliability. (2) GST in China showed little change from 1960–1980, but increased significantly across all regions from 1980 to 2000, with the increase rate slowed down except in the Qinghai–Tibet plateau (QTP) and southwest China after 2000. Notable GST increase is concentrated in colder regions, including the QTP, northeast (NEC), and northwest China (NWC). (3) Evapotranspiration (ET) and vapor pressure deficit were the primary drivers of annual GST variations at the regional scale, while their contributions to GST variations exhibited notable seasonal variability. Our findings could offer valuable scientific insights for addressing climate change, enhancing surface environmental models, and safeguarding ecological environments.

Spatial and Temporal analysis of Landsat data to Retrieve the NDWI, NDVI and Land Surface Temperature by thermal remote sensor: A case study of Hyderabad Metropolitan City, Telangana

Urban areas endure larger variations in ground surface temperature, vegetation, and water content than rural areas do due to the accelerated rise of technology, urbanization, and industrialization. These challenges could be investigated by using GIS and remote sensing tools. Using “LANDSAT 5 and LANDSAT 8 OLI/TIRS” data for Hyderabad from 2000 to 2020, this study evaluates changes in vegetation, water availability, and land surface temperature. Variations in NDVI, NDWI, and LST have been observed over time as a result of research on several parameters.Indices of water and vegetation are examined in this study where the Vegetation declined from 0.73006 to 0.49419 between 2000 and 2020, whereas water quantity decreased from 0.7979 to 0.4901 until 2010, at which point it progressively climbed to 0.7015 by that year. Likewise, studies on LST have demonstrated a connection between LST and NDWI. After rising to 40.9°C in 2010 from 39.8°C in 2000, temperatures decreased to 40°C in 2015 and 39.8°C in 2020.This work shows that LST, NDWI and NDVI can be accurately computed using GIS and remote sensing, which is helpful for environmental research and studies.

Use of Modified Tikhonov Regularization in Analysis of Ground Surface Temperature Variations

Inversion techniques employed in geothermal studies of ground surface temperature (GST) changes are known to have problems of instability and non-uniqueness in numerical solutions. In the present work it is pointed out that some of these difficulties can be overcome through the use of a method based on Tikhonov regularization of order one which imposes smoothing of main parameters. A major disadvantage of this approach is obliteration of weak thermal signals usually present at larger depths at the expense of strong ones present at relatively shallow depths. In the present work we consider a convenient way of minimizing this problem using a method based on Tikhonov regularization of order one. In this approach residuals of observational data are minimized by imposing constraints on the variations of smoothing parameters, that is controlled by the magnitude of regularization coefficients. This is accomplished in two stages of inversion. In the first stage we seek an estimation of the dates of climate events derived from results of temperature logs. Inversion of the second stage allows estimation of the magnitudes of GST variations that are compatible with the ages of climate events of the first stage. The advantage is in finding better solutions without introducing other artefacts on the climate history. Such two-stage Tikhonov regularization procedures has been employed for extracting complementary information on GST history in continental regions of Brazil. The results reveal that the main warming event of the last century has been preceded by several secondary events during the time period of 1400 to the 2000 A.D.

Spatial variations in ground surface temperature at various scales on the northeastern Qinghai-Tibet Plateau, China

Ground surface temperature (GST, depth of 5 cm) is essential for understanding the climate-induced impacts in the Earth Critical Zone, especially in cold regions. This work aims to detect the GST variability from fine (2 to 16 m) to local and landscape scales (2 and 50 km2) and along an 800-m elevational transect. The study area is located in the southern part of the Headwater Area of the Yellow River (HAYR), a representative area of discontinuous alpine permafrost on northeastern Qinghai-Tibet Plateau. From 2019 to 2020, GST was recorded at 39 sites under similar and varied environmental conditions. A statistically significant correlation was identified between mean annual GST (MAGST) with landcover (0.37, p < 0.05) and elevation (−0.76, p < 0.001). The analysis of variance (ANOVA) showed significant differences in MAGST between sites on bare ground and with vegetation. At the local/landscape scales, MAGSTs in meadows (−0.6 to 0.6 °C) were higher than those in swamp meadows (−1.4 to 0.7 °C) and bare grounds (−2.0, − 1.2 °C). At the fine scale, GST revealed a high similarity between plots (R2 > 0.95 for 90 % of the sites) but with an RMSE ranging from 0.25 to 1.5 °C. The intra-plot difference in MAGST was below 0.5 °C for sites with similar landcover in both plots and up to 1–2 °C when vegetation was compared to the bare ground. The decrease of MAGST with rising elevation was more pronounced for the sites in bare ground (R2 = 0.83, p < 0.001) than vegetated ones (e.g., meadow: R2 = 0.64, p < 0.003). These results help identify the patterns of permafrost distribution and thaw at a high spatial resolution and better understand their relationship with vegetation development, soil organic carbon, and the rapid landscape changes in the HAYR.

Diagnosing the subsurface buffer on ground-surface temperature under long-term groundwater pumping: effects of the bottom boundary condition placement

The terrestrial subsurface acts as a buffer in regulating land-surface water and energy processes. In integrated modeling with land-surface models, the regulating capacity of the subsurface is largely determined by the bottom boundary condition placement (BBCP). However, the sensitivity of land-surface processes to BBCP in Earth system modeling and integrated hydrologic modeling under conditions of human disturbance has not been investigated. In the research reported here, numerical experiments by integrated hydrologic modeling in the Little Washita Basin (Oklahoma, USA) were conducted to study the behavior of the subsurface buffer in regulating ground-surface temperature (GST) under long-term groundwater pumping and the role of BBCP in modeling such processes. Results reveal that long-term groundwater pumping weakens the subsurface buffer and leads to a warming trend. Under either sustainable or unsustainable pumping scenarios, the increase in GST exhibits temporal nonlinearity by rapidly increasing in the beginning and gradually achieving a dynamic equilibrium. It is also found that the subsurface buffer with deeper BBCP is more effective on damping the nonlinearity and the amplitude of the increase in GST. In addition, variations in GST are more sensitive to BBCP under pumping than in the natural state due to decreased thermal properties. In summary, this study diagnoses the subsurface buffer on variations of GST with the role of BBCP in integrated modeling under long-term groundwater pumping. These results are expected to have important implications on integrated modeling with land-surface models in areas of groundwater depletion worldwide.

Regional climate change signals inferred from a borehole temperature profile in Muli, Qilian Mountain, using the Tikhonov method

ABSTRACT Within the gas hydrate drilling project in the Qilian Mountain permafrost region, a temperature–depth profile measured from borehole DK-12 in Juhugeng of Muri Coalfield, Tianjun County, Qinghai Province, China, was analyzed to infer recent climate changes. The long-term surface temperature and thermal gradient were retrieved from borehole temperature measurements. The ground surface temperature (GST) changes were reconstructed by inversion of transient temperature perturbations through solving an inverse heat conduction problem using the Tikhonov method. Based on the instability of this kind of inverse problem and the nature of method-dependent features of borehole paleothermometry, we initially applied the Tikhonov regularization technique to obtain a stable past GST variation pattern with relatively low resolution. The inversion results showed that this region experienced temperature fluctuation with a total warming of 3°C (±1.6°C) from 1400 to the 2010s and a more exacerbated warming starting from the 1960s. The GST trend fit the surface air temperature observation trend from the nearest Yeniugou meteorological station. This work fills the gap created by limited meteorological records in the Muli area and extends knowledge of ground surface temperature trends going back more than ten centuries.

Recent climate changes in the northwestern Qaidam Basin inferred from geothermal gradients

Temperature perturbations under the ground surface are a direct thermal response to temperature changes on the ground surface. Thus, borehole temperature measurements can be used to reconstruct the temperature history of the ground surface using borehole Paleothermometry. In this study, we use seven borehole temperature profiles to reconstruct the ground surface temperature variation for the past 514 years in the Qaidam Basin, northwestern China. Borehole transient temperature measurements from seven sites in the northwestern Qaidam Basin were separated from the geothermal gradients and analyzed using the functional space inversion method to determine the ground surface temperature variation history of the region. All of the temperature profiles show the effects of recent climatic disturbances. The inversion reveals that during the last 514 years, the ground surface temperature has increased by an average of 1.2 °C (−0.11 to 2.21 °C). Clear signs of a cold period between 1500 and 1900 A.D. were found, which corresponds to the Little Ice Age. The coldest period occurred between 1780 and 1790 A.D. with a ground surface temperature of 5.4 °C. The reconstructed ground surface temperature shows an increasing trend during the 19th and the 20th centuries, but the temperature began to decrease in the late twentieth century. However, during the past 514 years, the highest temperature occurred in the 1990s. This reconstructed ground surface temperature variation history is verified by the simulated annual surface air temperature computed using EdGCM, while the cooling trend is confirmed by reconstructions of the winter half-year minimum temperatures from tree rings on the northeastern Tibetan Plateau.

Decoupled kinematics of two neighbouring permafrost creeping landforms in the Eastern Italian Alps

AbstractAn overall acceleration of rock glacier displacement rates in the Alps has been observed in recent decades, with several cases of destabilization leading to potential geomorphological hazards. This behaviour has been attributed to the rising permafrost temperature, induced by atmospheric warming and regulated by thermo‐hydrological processes. Landforms derived from the interaction of glacier remnants and permafrost are widespread in mountain areas, but are less studied and monitored than talus rock glaciers. This work presents a comparative study of a talus rock glacier and a glacial‐permafrost composite landform (GPCL) in the Eastern Italian Alps. The two landforms are only 10 km apart, but have rather different elevation ranges and main slope aspects. The kinematics and ground thermal conditions were monitored from 2001 to 2015 along with geomorphological surveys, analyses of historical maps and remote sensing data. The dynamic behaviour of the rock glacier was similar to the majority of monitored rock glaciers in the Alps, with an acceleration after 2008 and a velocity peak in 2015. In contrast, the GPCL had a nearly unchanged displacement rate during the observation period. Statistical analyses of kinematic vs. nivo‐meteorological variables revealed a dynamic decoupling of the two landforms after 2008 that corresponds with increased winter snow accumulation. Although the kinematics of both landforms respond to ground surface temperature variations, the collected evidence suggests a different reaction of ground surface temperature to variations in the precipitation regime. This different reaction is likely due to local topo‐climatic conditions that affect snow redistribution by wind. The different reactions of the two systems to the same climatic forcing is likely a legacy of their different origins. GPCL dynamics result from interaction of permafrost and residual glacial dynamics that are associated with possible peculiarities in the internal/basal meltwater circulation, whose future response is uncertain and requires improved understanding. © 2019 John Wiley &amp; Sons, Ltd. © 2019 John Wiley &amp; Sons, Ltd.

Influence of an internal heat exchanger on the operation of a CO2 direct expansion ground source heat pump

In this work, the influence of an internal heat exchanger (IHE) on the operation of a CO2 direct expansion ground source heat pump (DX-GSHP) was assessed through transient energy simulations. A previous theoretical model was extended to account for an IHE, and was used to evaluate the performance of DX-GSHP systems under various controls, ground conditions and building loads. A showcase of the benefit of integrating an IHE to the DX-GSHP was carried out, through 4-month heating energy simulations period of a small residential building located in Canada, under 4 different cases. Results show that adding an IHE to the system effectively counters the effect of thermal short-circuiting in the borehole as well as ground surface temperature variations, and thereby increases its efficiency.

Borehole thermal energy storage systems under the influence of groundwater flow and time-varying surface temperature

A 3D finite element model of circular borehole cluster connected in series is used as a response model to generate normalized transfer functions of a borehole thermal energy storage system under the influence of ground surface temperature variations and groundwater flow. Two response functions are obtained by convolving transfer functions of the system's outlet fluid temperature with two incremental input functions describing the temperature variation of the inlet and outlet fluid and variations of the ground surface temperature. Superposition is applied to obtain the resulting fluid temperature with respect to thermal inputs at the inlet fluid and the ground surface over the course of ten years and results are compared for various groundwater velocities. This work demonstrates that the combined effect of groundwater flow and ambient air temperature variations can significantly decrease the performance of a BTES system. The methodology used can be extended to simulate complex system.

Using distributed temperature sensing to monitor field scale dynamics of ground surface temperature and related substrate heat flux

We present one of the first studies of the use of distributed temperature sensing (DTS) along fibre-optic cables to purposely monitor spatial and temporal variations in ground surface temperature (GST) and soil temperature, and provide an estimate of the heat flux at the base of the canopy layer and in the soil. Our field site was at a groundwater-fed wet meadow in the Netherlands covered by a canopy layer (between 0 and 0.5m thickness) consisting of grass and sedges. At this site, we ran a single cable across the surface in parallel 40m sections spaced by 2m, to create a 40m×40m monitoring field for GST. We also buried a short length (≈10m) of cable to depth of 0.1±0.02m to measure soil temperature. We monitored the temperature along the entire cable continuously over a two-day period and captured the diurnal course of GST, and how it was affected by rainfall and canopy structure. The diurnal GST range, as observed by the DTS system, varied between 20.94 and 35.08°C; precipitation events acted to suppress the range of GST. The spatial distribution of GST correlated with canopy vegetation height during both day and night. Using estimates of thermal inertia, combined with a harmonic analysis of GST and soil temperature, substrate- and soil-heat fluxes were determined. Our observations demonstrate how the use of DTS shows great promise in better characterizing area-average substrate/soil heat flux, their spatiotemporal variability, and how this variability is affected by canopy structure. The DTS system is able to provide a much richer data set than could be obtained from point temperature sensors. Furthermore, substrate heat fluxes derived from GST measurements may be able to provide improved closure of the land surface energy balance in micrometeorological field studies. This will enhance our understanding of how hydrometeorological processes interact with near-surface heat fluxes.

Development and validation of a Slinky™ ground heat exchanger model

Ground source heat pump systems are an energy efficient heating and cooling technology for residential and commercial buildings. The main barrier to adoption is the higher investment cost compared to conventional systems. Where available land area permits, horizontal ground heat exchangers are generally less expensive than vertical borehole-type ground heat exchangers (GHXs). A further cost reduction can be made by using Slinky™ GHXs, which require less trench space and hence reduce the installation cost, in many cases. It is desirable to formulate an accurate model for simulation purposes; such simulations can be used in both design tools and in energy analysis programs.The model formulated in this paper relies on analytical ring source solutions to compute temperature response functions for both horizontal and vertical Slinky™ heat exchangers. The algorithms used to calculate the response factors have several features that significantly increase computation speed. The thermal effect of the ground surface temperature variation on the GHXs is considered by superimposing the undisturbed ground temperature, which is calculated using the numerical approach. For use in system simulations where the GHX may be connected to other components, the model is formulated to calculate both heat transfer rate and exiting fluid temperature, given entering fluid temperature. The model has been validated against the previously published field test data.

Fundamental solution method for reconstructing past climate change from borehole temperature gradients

Deep borehole temperature profiles have successfully been used to reconstruct past ground surface temperature history and the results are dependent on the inversion methods. These methods are tedious and sometimes unstable in iterative computation. In this paper, we propose a new fundamental solution method to reconstruct the past ground surface temperature variation, which depends on the assumption that ground temperature field in a homogeneous region is governed by a one-dimensional heat conductive equation. To regularize the resultant ill-conditioned linear system of equations, we apply successfully both the Tikhonov regularization technique and the generalized cross validation parameter choice rule to obtain a stable approximation solution of the ill-posed inverse problem. Our new method is stable and meshless, and it does not require iteration. We conducted idealized simulations with good results. We also used in-situ borehole data of RU-Yakutia329 from Yakutia, Siberia and CN-XZ-naqu903 from Naqu, Qinghai–Xizang (Tibetan) Plateau to validate our new approach. Results from these borehole studies show a warming of 0.1 and 2.3°C, respectively, in the past 450years. When comparing to the results from previous studies, the RU-Yakutia329 study has the same magnitude of warming, while the magnitude of warming at Naqu is slightly smaller.

Inferred gas hydrate and permafrost stability history models linked to climate change in the Beaufort-Mackenzie Basin, Arctic Canada

Abstract. Atmospheric methane from episodic gas hydrate (GH) destabilization, the "clathrate gun" hypothesis, is proposed to affect past climates, possibly since the Phanerozoic began or earlier. In the terrestrial Beaufort-Mackenzie Basin (BMB), GHs occur commonly below thick ice-bearing permafrost (IBP), but they are rare within it. Two end-member GH models, where gas is either trapped conventionally (Case 1) or where it is trapped dynamically by GH formation (Case 2), were simulated using profile (1-D) models and a 14 Myr ground surface temperature (GST) history based on marine isotopic data, adjusted to the study setting, constrained by deep heat flow, sedimentary succession conductivity, and observed IBP and Type I GH contacts in Mallik wells. Models consider latent heat effects throughout the IBP and GH intervals. Case 1 GHs formed at ~0.9 km depth only ~1 Myr ago by in situ transformation of conventionally trapped natural gas. Case 2 GHs begin to form at ~290–300 m ~6 Myr ago in the absence of lithological migration barriers. During glacial intervals Case 2 GH layers expand both downward and upward as the permafrost grows downward through and intercalated with GHs. The distinctive model results suggest that most BMB GHs resemble Case 1 models, based on the observed distinct and separate occurrences of GHs and IBP and the lack of observed GH intercalations in IBP. Case 2 GHs formed &gt;255 m, below a persistent ice-filled permafrost layer that is as effective a seal to upward methane migration as are Case 1 lithological seals. All models respond to GST variations, but in a delayed and muted manner such that GH layers continue to grow even as the GST begins to increase. The models show that the GH stability zone history is buffered strongly by IBP during the interglacials. Thick IBP and GHs could have persisted since ~1.0 Myr ago and ~4.0 Myr ago for Cases 1 and 2, respectively. Offshore BMB IBP and GHs formed terrestrially during Pleistocene sea level low stands. Where IBP is sufficiently thick, both IBP and GHs persist even where inundated by a Holocene sea level rise and both are also expected to persist into the next glacial even if atmospheric CO2 doubles. We do not address the "clathrate gun" hypothesis directly, but our models show that sub-IBP GHs respond to, rather than cause GST changes, due to both how GST changes propagates with depth and latent heat effects. Models show that many thick GH accumulations are prevented from contributing methane to the atmosphere, because they are almost certainly trapped below either ice-filled IBP or lithological barriers. Where permafrost is sufficiently thick, combinations of geological structure, thermal processes and material properties make sub-IBP GHs unlikely sources for significant atmospheric methane fluxes. Our sub-IBP GH model histories suggest that similar models applied to other GH settings could improve the understanding of GHs and their potential to affect climate.

Thermal Protection of a Ground Layer With Phase Change Materials

Conventional ground surface insulation can be used to protect power line foundations in permafrost regions from the adverse effects of seasonal freezing and thawing cycles. But previous studies have shown ineffective thermal protection against the receding permafrost with conventional insulation. In this paper, an alternative thermal protection method (phase change materials (PCMs)) is analyzed and studied experimentally. Seasonal ground temperature variations are estimated by an analytical conduction model, with a sinusoidal ground surface temperature variation. A compensation function is introduced to predict temperature variations in the foundation, when the ground surface reaches a certain temperature profile. Measured data are acquired from an experimental test cell to simulate the tower foundation. With thermal energy storage in the PCM layer, the surface temperature of the soil was modified, leading to changes in temperature in the foundation. Measured temperature data show that the PCM thermal barrier effectively reduces the temperature variation amplitude in the foundation, thereby alleviating the seasonal freezing and thawing cycles. Different thermal effects of the PCM thermal barrier were obtained under different air temperature conditions. These are analyzed via melting degree hours and freezing degree hours, compared with a critical number of degree hours.

Ground surface temperature variations on Kunashir Island in the last 400 years inferred from borehole temperature data and tree-ring records

Ground surface temperature variations on Kunashir Island in the last 400 years inferred from borehole temperature data and tree-ring records

Transient thermal effects in Alpine permafrost

Abstract. In high mountain areas, permafrost is important because it influences the occurrence of natural hazards, because it has to be considered in construction practices, and because it is sensitive to climate change. The assessment of its distribution and evolution is challenging because of highly variable conditions at and below the surface, steep topography and varying climatic conditions. This paper presents a systematic investigation of effects of topography and climate variability that are important for subsurface temperatures in Alpine bedrock permafrost. We studied the effects of both, past and projected future ground surface temperature variations on the basis of numerical experimentation with simplified mountain topography in order to demonstrate the principal effects. The modeling approach applied combines a distributed surface energy balance model and a three-dimensional subsurface heat conduction scheme. Results show that the past climate variations that essentially influence present-day permafrost temperatures at depth of the idealized mountains are the last glacial period and the major fluctuations in the past millennium. Transient effects from projected future warming, however, are likely larger than those from past climate conditions because larger temperature changes at the surface occur in shorter time periods. We further demonstrate the accelerating influence of multi-lateral warming in steep and complex topography for a temperature signal entering the subsurface as compared to the situation in flat areas. The effects of varying and uncertain material properties (i.e., thermal properties, porosity, and freezing characteristics) on the subsurface temperature field were examined in sensitivity studies. A considerable influence of latent heat due to water in low-porosity bedrock was only shown for simulations over time periods of decades to centuries. At the end, the model was applied to the topographic setting of the Matterhorn (Switzerland). Results from idealized geometries are compared to this first example of real topography, and possibilities as well as limitations of the model application are discussed.

Reconstruction of the thermal environment evolution in urban areas from underground temperature distribution

It is possible to estimate the ground surface temperature (GST) history of the past several hundred years from temperature profiles measured in boreholes because the temporal variation in GST propagates into the subsurface by thermal diffusion. This “geothermal method” of reconstructing GST histories can be applied to studies of thermal environment evolution in urban areas, including the development of “heat islands.” Temperatures in boreholes were logged at 102 sites in Bangkok, Jakarta, Taipei, Seoul and their surrounding areas in 2004 to 2007. The effects of recent surface warming can be recognized in the shapes of most of the obtained temperature profiles. The preliminary results of reconstruction of GST histories through inversion analysis show that GST increased significantly in the last century. Existing temperature profile data for the areas in and around Tokyo and Osaka can also be used to reconstruct GST histories. Because most of these cities are located on alluvial plains in relatively humid areas, it is necessary to use a model with groundwater flow and a layered subsurface structure for reconstruction analysis. Long-term records of subsurface temperatures at multiple depths may demonstrate how the GST variation propagates downward through formations. Time series data provide information on the mechanism of heat transfer (conduction or advection) and the thermal diffusivity. Long-term temperature monitoring has been carried out in a borehole located on the coast of Lake Biwa, Japan. Temperatures at 30 and 40 m below the ground surface were measured for 4 years and 2 years, respectively, with a resolution of 1 mK. The obtained records indicate steady increases at both depths with different rates, which is probably the result of some recent thermal event(s) near the surface. Borehole temperatures have also been monitored at selected sites in Bangkok, Jakarta, and Taiwan.

Recent climate variations in the subarctic inferred from three borehole temperature profiles in northern Quebec, Canada

Three temperature depth profiles recorded in permafrost in northern Quebec, Canada, were used to infer the ground surface temperature history (GSTH) of the region. The site is located in a barren rock desert on the Katinniq plateau at an elevation of 600 m, near the northern tip of the Ungava Peninsula. The boreholes were logged more than 3 yr after drilling was completed, insuring that the holes had returned to thermal equilibrium. Thermal conductivity measurements were made on core samples. Radiogenic heat production is small and can be neglected. The temperature depth profiles show marked deviations from steady state in the upper 200 m that are assumed to be caused by recent (< 300 yr) variations in ground surface temperature. The GSTHs obtained by inversion of the three temperature profiles consistently show warming by ∼ 2.5 K, but differ significantly in the details. One profile which is least affected by topographic effects and thermal conductivity changes was analyzed in great details with different inversion methods; direct methods were also used to verify how well the GSTH can be resolved by the data. The results show a marked warming (≈ 1.4 K) between the mid-1700s and 1940, followed by a cooling episode (≈ 0.4 K) which lasted 40–50 yr, followed by a sharp ≈ 1.7 K warming over the past 15 yr. The borehole temperature measurements suggest that most of this warming occurred over the past 15 yr. These results are in agreement with the available meteorological records and proxy data.

Simulating Active Layer Thaw in a Boreal Environment

A large part of the boreal zone of the western Canadian Arctic is underlain by ice-rich discontinuous permafrost which when thawed, can lead to settlement of the ground surface that has implications for the integrity of northern infrastructure, including oil and gas pipelines. A simple yet physically-based model is desired to simulate thawing of the active layer in different materials commonly found along the Mackenzie Valley pipeline corridor. Stefan’s algorithm determines the phase change of soil moisture using ground surface temperature as the upper boundary condition and conduction to transfer heat to the freeze-thaw front. It is tested on a permafrost site near Wrigley, Northwest Territories, where the computed thaw penetration compares satisfactorily with field data. To further explore the effects of climate and soil types on active layer depth, three representative sites in the Mackenzie valley where ground surface temperatures are available were selected for simulation of ground thaw, under two summer conditions. Results of the simulation demonstrate the sensitivity of active layer thaw to (1) soil materials due to differential thermal properties, (2) moisture content, which largely controls the latent heat requirement for phase change, and (3) inter-annual variations in ground surface temperature. Given the strong potential for environmental changes in the vast boreal region, the model allows the active layer thaw responses to be easily assessed.