Heat Transfer In Soil Research Articles

Comprehensive analysis of thermo-mechanical responses in collapsible soil under varied water content conditions

AbstractIn this research, the effect of both temperature gradients and varied water content on heat transfer in collapsible soil is investigated. The study based on one-dimensional laboratory setup, soil temperature distribution in proximity to a heat source, was examined across four distinct temperatures (ranging from 50 to 200 °C) under varying water content (0%, 10%, 15%, and 20%). Through steady-state conditions and extended measurements over days, data were collected to compare soil thermal conductivity at 10% water content using two different methods. The first method required some of soil characteristics, such as dry density and optimum water content, while the second method relied on heating parameters and supplied heating content. A robust agreement between thermal conductivity values obtained through these two methods was observed. Correlations from experimental data were analyzed to enrich understanding, and multivariate linear regression was employed to predict the thermal conductivity and resistivity of collapsible soils. Results indicated that the higher soil density, the increasing the thermal conductivity, whereas greater soil porosity exhibited the opposite trend. Elevated temperatures were found to enhance soil density, influencing the spatiotemporal distribution of heat within the soil. This research contributes valuable insights into the dynamic behavior of heat transfer in collapsible soil, emphasizing the complex interaction of temperature gradients and water content variations. The findings of this study can advance the development of efficient and sustainable geothermal systems in regions with collapsible soils, potentially enhancing the design and management of structures built on such soils, especially in arid and semi-arid areas.

Accurate identification of soil thermal parameters and groundwater flow from thermal response tests

The soil heat transfer parameters constitute the key information required for designing ground source heat pump (GSHP). Due to the simplification of the common analytical models, traditional methods are difficult to achieve accurate identification of soil thermal parameters and seepage velocity simultaneously. In this work, a high-precision method to simultaneously identify soil thermal conductivity, volumetric heat capacity, and seepage velocity based on deep neural network is proposed. Through the inversed orthogonal method, the training and validation samples are obtained from a large number of thermal response tests (TRTs) on a full-scale simulation platform. The accuracy of this method was verified by comparing identification results with the true values. Meanwhile, the uncertainty of identification results under different noise conditions was quantified, and the impact of test duration was discussed. The results showed that when the maximum random noise is 0.1 °C, the identification errors of the thermal conductivity, volumetric heat capacity, and seepage velocity are only 1.14 %, −4.34 %, and −3.08 %, respectively. The identification reliability can be improved by obtaining the average value of the results under multiple tests and extending the test duration. When the test duration increased from 50 to 100 h, the uncertainty of the identified parameters reduced by 54.57 %, 48.41 %, and 65.70 %, respectively.

Thermal performance of energy piles in unsaturated soils: Experiment, simulation, and case study

The operation of energy piles in unsaturated soils involves coupled heat and moisture transfer, demanding further detailed investigation. In this paper, laboratory tests were conducted to validate a numerical model that incorporated vapor and liquid migration, convection, and latent heat transfer in unsaturated soils. Moreover, this model captured the dynamic variation in characteristic parameters of unsaturated soils. Building upon this observation, this study delved into the thermal performance of the energy pile under ten-year cooling and heating cycles, specifically focusing on the temperature, heat exchange rate, volumetric water content, and thermal conductivity. It is demonstrated that the imbalanced cooling and heating load adversely affects the long-term operation. In particular, the cooling power experiences a reduction of 15.1% after ten years of operation. The results indicate that higher soil temperatures positively impact the heat exchange rate in heating mode, while rainfall facilitates heat transfer in both seasons. Furthermore, a case study of an energy pile system was carried out, encompassing load calculation, pile group simulation, economic analysis, and design optimization. A comprehensive evaluation of the technical and economic feasibility demonstrates that the system exhibits excellent performance, particularly when the ratio of cooling and heating loads ranges from 1.1 to 1.3.

Heated fibre optics to monitor soil moisture under successive saturation–drying cycles: An experimental approach

AbstractIn recent decades, distributed temperature sensing (DTS) has emerged as a robust technology for environmental applications, enabling high‐resolution temperature measurements along fibre optic cables (FOCs). The actively heated fibre optic (AHFO) method is employed to monitor soil moisture (, m3 m−3), wherein the soil temperature subsequent to the application of a heat pulse is measured by a DTS (AHFO‐DTS approach). Despite significant improvements in the application of AHFO‐DTS under controlled and natural conditions, the thermal behaviour of soil during multiple saturation–natural drying cycles has been insufficiently evaluated. This study aimed to address this gap by constructing an experimental horizontal soil profile in the laboratory for the application of the AHFO‐DTS method during two successive saturation–drainage–evaporation (SDE) cycles. Three heating strategies were applied to a metallic alloy in contact with a FOC, and calibration models were used to correlate with the thermal conductivity (), cumulative temperature increase (), and maximum temperature increase (). The results indicated that during the second SDE cycle, the highest errors in estimates were observed with the low power‐short heat pulse, whereas the application of the low power‐long duration and high power‐short duration pulses improved the accuracy of calculations. Additionally, errors in estimates escalated under wetter conditions, attributed to a shift in soil heat transfer capacity from the first to the second SDE cycle for > 0.10 m3 m−3. This behaviour was ascribed to thermal hysteresis, arising from the contact resistance of the FOC and the alloy with the surrounding soil. Furthermore, the method exhibited the least sensitivity to this effect and yielded reliable estimates, thus its adoption is recommended. Moreover, the use of the low power‐long duration heating strategy is suggested as it promotes a trade‐off between energy saving and accurate estimates. We concluded that assessing soil thermal response under multiple SDE cycles enhances the comprehension of the AHFO‐DTS method. Overall, our findings provide insights into enhancing the applicability of this approach under field conditions, particularly following irrigation schedules and natural rainfall events.

Evaluation of Soil Heat Transfer in Relation to Climate Variability across Umudike, Abia State, Nigeria

Evaluation of Soil Heat Transfer in Relation to Climate Variability across Umudike, Abia State, Nigeria

Use of electrical resistivity tomography measurements for investigation of different grouting materials for very shallow geothermal applications within varying seasonal conditions; Applied on a geothermal earth-air heat exchanger system

To achieve the current climate targets, heat pump systems like very shallow geothermal applications are gaining ground. However, the dimensioning of these ground coupled systems is soil-dependent and thus subject to significant differences in efficiency. Furthermore, the thermal properties of the grouting materials are essential for heat transfer in the direct vicinity of the geothermal application. To provide a non-invasive assessment of relevant soil and grouting characteristics, electrical resistivity tomography (ERT) measurements were performed.In this case, the surrounding of an Earth Air-Heat Exchanger – system (EAHE) with different grouting materials (fine sand and fine sand with bentonite) was investigated. For investigation the electrical resistivity (ER) of initial and modified soil conditions were measured regarding soil texture and moisture content. Thereby, the different grouting materials are clearly identified. Thus, based on the ERT measurements, a characterisation of key soil and grouting material properties for applications focusing on heat transfer in soil has been carried out.Furthermore, the depth of soil disturbance due to the EAHE installation could have been traced.Due to a monitoring over different season (February and May) changes in raw ER data could have been ascribed to temperature changes.

Numerical study of soil heat and moisture migration in seasonal ground heat storage

Heat and moisture transfer is an important factor leading to soil drying shrinkage and heat transfer attenuation in the process of seasonal soil heat storage with high temperature. The purpose of this study is to establish a numerical model to explore the characteristic of heat and moisture migration in heat storage soil. The numerical model is verified by the experimental data. In this study, two months heat storage with high-temperature (80℃) and five months heat extraction with low-temperature (20℃) seasonal operation period was simulated, and the changes in the temperature and moisture content of the heat storage soil were analyzed. After a seasonal period, the mean temperature in the backfill and the original soil would increase. The moisture content in original soil would increase, while the moisture content in the backfill would decrease. For the typical backfill with 0.4 m diameter, the obvious heat and moisture migration phenomenon only occurs in the backfill and the part of the original soil close to the backfill.

Coupled heat and water transfer in heterogeneous and deformable soils: Numerical model using mixed finite element method

We present a generic model framework for coupled heat and water transfer (CHWT) in deformable (non-rigid) soils with spatial variations of soil properties. The model backbone is a mixed finite element method (FEM), which solves the Philip and de Vries (1957) CHWT model and achieves conservation of mass and energy on both local and global scales. Spatial variations occur in soil hydraulic and thermal properties due to transient water content and temperature distributions. Based on the mixed FEM scheme, a gradient measure and a clustering model (“k-means”) are proposed to trace the regions with large spatial variations of soil properties, and an adaptive mesh refinement technique is developed to improve the spatial resolution and simulation accuracy. Deformation perturbates local soil topography and alters transient soil water and temperature regimes in the deformed regions. A quasi-static deformation model is presented, and the deformation effects are incorporated into the mixed FEM scheme. When external load exists, soil deformation is simulated with an updated Lagrangian formulation, and the local water content and temperature variations due to soil volume changes are also updated in the CHWT model. Numerical examples, including thermally induced soil water transfer and water infiltration, illustrate the model ability to provide plausible CHWT results, especially the refined solutions near the wetting fronts and the water content and temperature distributions when the soil is deformable. In conclusion, the proposed model framework provides an effective pipeline to incorporate and process the spatial variations of soil properties and soil deformation in CHWT simulations.

Non-local modelling of freezing and thawing of unsaturated soils

A large part of the earth’s surface is covered by seasonally or permanently frozen soils. Considering the negative impact of climate change, future development of such regions can be underpinned by mathematical methods for accurate analysis of heat and moisture transport in freezing and thawing soils. Reported in this paper is a novel non-local formulation of water and heat transport in unsaturated soils. The formulation uses bond-based peridynamics (PD) and consists of a set of integral–difference formulations of energy and mass conservation. Specific features of freezing/thawing soils are incorporated by a combination of van Genuthcen and Clausius–Clapeyron relations. Computational results are compared with four sets of laboratory experiments to demonstrate the efficiency of the developed approach. The model can be used to analyse the effect of water flow on heat transfer in soils during thawing of permafrost soils. Further, it can be applied in modelling climate change effects, and can be used for construction of coupled physically justified models of frost heave.

New insights into the correlation between soil thermal conductivity and water retention in unsaturated soils

AbstractThe heat transfer and water retention in soils, governed by soil thermal conductivity (λ) and soil water retention curve (SWRC), are coupled. Soil water content (θ) significantly affects λ. Several models have been developed to describe λ(θ) relationships for unsaturated soils. Ghanbarian and Daigle presented a percolation‐based effective‐medium approximation (P‐EMA) for λ(θ) with two parameters: scaling exponent (ts) and critical water content (θc). In this study, we explored the new insights into the correlation between soil thermal conductivity and water retention using the P‐EMA and van Genuchten models. The θc was strongly correlated to selected soil hydraulic and physical properties, such as water contents at wilting point (θpwp), inflection point (θi), and hydraulic continuity (θhc) determined from measured SWRCs for a 23‐soil calibration dataset. The established relationships were then evaluated on a seven‐soil validation dataset to estimate θc. Results confirmed their robustness with root mean square error ranging from 0.011 to 0.015 cm3 cm−3, MAE ranging from 0.008 to 0.013 cm3 cm−3, and R2 of 0.98. Further discussion investigated the underlying mechanism for the correlation between θc with θhc which dominate both heat transfer and water flow. More importantly, this study revealed the possibility to further investigate the general relationship between λ(θ) and SWRC data in the future.

Modelling artificial ground freezing subjected to high velocity seepage

Artificial ground freezing (AGF) is a ground improvement technique for ensuring the safety of underground construction works in water-bearing soils. High velocity water transport in coarse-grain soils can prevent the ice wall formation in brine-based ground freezing methods. This can be overcome by using expendable refrigerants such as solid carbon dioxide and liquid nitrogen, which provide much lower temperatures. Presented here is a model for analysis and design of ground freezing by expendable refrigerants under high velocity seepage conditions. Non-local mathematical formulations of heat transfer and water flow in soils are developed within the framework of the Peridynamics theory. Their computational implementation uses an adaptive multi-grid peridynamic approach to analyse large domains efficiently. The simulations are tested successfully against several benchmarks. The developed model enables reliable analyses of the effects of main geological and technological parameters on the ice-wall delivery in the presence of groundwater flow.

Natural convection effect on heat transfer in saturated soils under the influence of confined and unconfined subsurface flow

Recently, it has been proven that natural convection significantly impacts heat transfer close to geothermal systems in saturated soils even in the presence of groundwater flow. However, this phenomenon has only been investigated in the presence of confined groundwater flow. Therefore, in this study, a fully coupled hydro-thermal model was developed to quantitatively determine the natural convection influence on heat transfer in the presence of an unconfined groundwater flow and to compare the hydro-thermal response of soil under these two different scenarios. Results showed that natural convection influence depends on the coupled effects of soil permeability, groundwater velocity, and heater temperature. According to the results, in the case of a groundwater flow velocity less than 10−7 m/s, natural convection role is non-negligible when Rayleigh number is greater than 50, while for other groundwater velocities, that matters only when Buoyancy ratio is greater than 20. It was also shown that choosing a confined groundwater flow over an unconfined one led to an error of 47 % to 173 % in the explored scenarios. Furthermore, it was revealed that when the relative distance of the heater from the surface alters from 0 to 15 and 30 m, the error in the soil temperature due to neglecting natural convection can be as high as 43 %, 48 %, and 60 %, respectively.

Thermo-mechanical behaviour of microbial induced carbonate precipita-tion (MICP) sand for geothermal pavements

Introduction
 Ground source heat pump (GSHP) or shallow geothermal energy systems are gaining attention for helping combat global warming and the negative effects of urbanisation caused by human activities. In recent decades, energy geo-structure techniques have developed by using subsurface infrastructures to exchange heat with the ground. These techniques can provide space heating and cooling while still preserving the primary structural function. As a result, they have become a valuable part of geothermal energy systems. Researchers have developed an understanding of incorporating ground heat exchangers into foundation piles, retaining walls, and tunnel linings with modest additional cost [1-4]. Pavements are also structures in contact with the ground that have the potential to be used as energy geo-structures (i.e., geothermal pavements), yet, their use has not been extensively studied [5-8].
 Soil thermal conductivity is an important factor influencing the efficiency of geothermal pavements since heat transfer in soils occurs primarily by conduction [9]. Microbially induced calcium carbonate (CaCO3) precipitation (MICP) is an innovative technique for strengthening sandy soils by coating and binding soil grains with calcium carbonate crystals. The distribution and arrangement of the CaCO3 within the pore spaces play a crucial role in determining the resulting strength of the treated sand. In addition, these crystals can act as thermal bridges to enhance the soil's thermal conductivity [10]. Combining geothermal pavements with MICP sand is still nascent, and the limited number of studies that exist mainly focus on the associated thermal property changes [11]. However, since the principal function of pavements is transmitting (dynamic) loads to the subbase and the underlying soil, the thermal conductivity of the MICP-treated pavement may vary as a result of the applied mechanical loads (e.g., due to the partial or total loss of thermal bridges and/or particle rearrangement). This research thus investigates the changes in the thermal conductivity of MICP-treated sands as they are subjected to quasi-static triaxial compression. The experimental results collected can deepen our understanding of the thermo-mechanical behaviour of MICP-treated sands and provide practical insights for using MICP to reinforce the subbase or underlying soil of geothermal pavements.
 Methodology
 This research performed a series of quasi-static triaxial tests on MICP-treated Houston sand, fine-grained, high-purity silica sand. Sporosarcina pasteurii (strain designation DSM 33) was used for the MICP treatment of the soil specimen. To study the effect of CaCO3 content on the thermo-mechanical performance of MICP-treated sand, three cementation solution treatment cycles were applied, yielding theoretical CaCO3 contents of 0.6%, 1.6% and 2.7% by weight, respectively. Details on the MICP treatment of the samples can be found in [12]. Samples for triaxial testing were treated in cylindrical tubes of 50mm inner diameter and 100mm height. To investigate the influence of the CaCO3 content on the soil thermal conductivity, MICP-treated specimens were air-dried prior to triaxial testing Triaxial tests were subsequently conducted in dry conditions to isolate the effect of the MICP and avoid the influence of water content on soil thermal conductivity (λ). Furthermore, a new miniaturised transient sensor was embedded in the triaxial samples to monitor the λ changes during the sharing phase [12].
 Results
 An example of the evolution of the deviatoric stress with axial strain under 50kPa confining stress (σ3) in the triaxial cell is shown in Figure 1a. Compared to the untreated sand, MICP-treated samples lead to higher peak strength and stiffness. Importantly, λ changes during triaxial testing for different CaCO3 contents are summarised in Figure 1b. Results indicate that the increase in CaCO3 content can significantly improve λ, and that λ rapidly decreases post-peak strength due to dilation and CaCO3 bond breakage. Once the samples reach its ultimate state, λ remains unchanged.

Numerical Study of Coupled Water and Vapor Flow, Heat Transfer, and Solute Transport in Variably‐Saturated Deformable Soil During Freeze‐Thaw Cycles

AbstractAs climate change intensifies, soil water flow, heat transfer, and solute transport in the active, unfrozen zones within permafrost and seasonally frozen ground exhibit progressively more complex interactions that are difficult to elucidate with measurements alone. For example, frozen conditions impede water flow and solute transport in soil, while heat and mass transfer are significantly affected by high thermal inertia generated from water‐ice phase change during the freeze‐thaw cycle. To assist in understanding these subsurface processes, the current study presents a coupled two‐dimensional model, which examines heat conduction‐convection with water‐ice phase change, soil water (liquid water and vapor) and groundwater flow, advective‐dispersive solute transport with sorption, and soil deformation (frost heave and thaw settlement) in variably saturated soils subjected to freeze‐thaw actions. This coupled multiphysics problem is numerically solved using the finite element method. The model's performance is first verified by comparison to a well‐documented freezing test on unsaturated soil in a laboratory environment obtained from the literature. Then based on the proposed model, we quantify the impacts of freeze‐thaw cycles on the distribution of temperature, water content, displacement history, and solute concentration in three distinct soil types, including sand, silt and clay textures. The influence of fluctuations in the air temperature, groundwater level, hydraulic conductivity, and solute transport parameters was also comparatively studied. The results show that (a) there is a significant bidirectional exchange between groundwater in the saturated zone and soil water in the vadose zone during freeze‐thaw periods, and its magnitude increases with the combined influence of higher hydraulic conductivity and higher capillarity; (b) the rapid dewatering ahead of the freezing front causes local volume shrinkage within the non‐frozen region when the freezing front propagates downward during the freezing stage and this volume shrinkage reduces the impact of frost heave due to ice formation. This gradually recovers when the thawed water replenishes the water loss zone during the thawing stage; and (c) the profiles of soil moisture, temperature, displacement, and solute concentration during freeze‐thaw cycles are sensitive to the changes in amplitude and freeze‐thaw period of the sinusoidal varying air temperature near the ground surface, hydraulic conductivity of soil texture, and the initial groundwater levels. Our modeling framework and simulation results highlight the need to account for coupled thermal‐hydraulic‐mechanical‐chemical behaviors to better understand soil water and groundwater dynamics during freeze‐thaw cycles and further help explain the observed changes in water cycles and landscape evolution in cold regions.

Experimental and Theoretical Study of the Influence of Saline Soils on Frozen Wall Formation

This paper examines the impact of salinity on the thermophysical properties of soils during artificial freezing. It focuses on analyzing heat and mass transfer in saline soils for constructing a frozen wall around a mineshaft at a potash salt deposit. The presence of salts in the groundwater near the contact point with water-protective strata is common in these deposits. Experimental studies were conducted on clay, chalk, and sand to understand the effect of salinity on the freezing temperature, unfrozen water content, specific heat capacity, and thermal conductivity of wet soil. These findings were used to simulate heat and mass transfer in saline soils using a one-dimensional model. The technique of circumferential averaging was introduced to account for the thermal impact of freeze pipes. The results indicate that higher soil salinity leads to a faster decrease in soil temperature under freezing conditions, although this dependence is weak for clay. This study also revealed that an increase in initial salinity results in a reduction in the thickness of the frozen wall. It was found that, for chalk and sand, there exists a range of initial salinity during which the frozen wall’s thickness is almost independent of the initial salinity.

Simulation of Soil Temperature under Plateau Zokor's (Eospalax baileyi) Disturbance in the Qinghai Lake Watershed, Northeast Qinghai-Tibet Plateau.

The soil temperature is a key factor affecting the fragile terrestrial ecosystems on the Qinghai-Tibet Plateau, and has been remarkably altered by the soil mammal's disturbance. This study first analyzed the soil temperature variation in grassland, mound, and bald patch under the disturbance of plateau zokor (Eospalax baileyi) from October 2018 to July 2020 in the Qinghai Lake watershed. Then, the SHAW (simultaneous heat and water) model was used to simulate the soil temperature change of three land surface types, and the sensitivity of soil temperature to environmental parameters before and after the disturbance was explored. The results showed the following: (1) The daily range of soil temperature was mound > bald patch > grassland, which became smaller as the depth increased, due to the co-influence of vegetation coverage and soil bulk density. There was an obvious hysteresis of soil heat transfer for grassland, as compared with mound and bald patch, especially at 5 and 15 cm depths. (2) The SHAW model was applicable for the simulation of soil temperature under the plateau zokor's disturbance, especially during the growing season, and had better simulation accuracy for deep soil. (3) Air-entry potential and pore-size distribution index obviously affected soil temperature change, because of the change in root system and soil pores under the plateau zokor's disturbance. With the evolution of disturbance process, the response of soil temperature to the leaf area index weakened gradually, owing to the different duration of disturbance and restoration. In general, the plateau zokor's disturbance alters the soil properties and vegetation characteristics, and further, distinctly affects heat transfer and soil temperature.

Dimensionless characterization of the problem of heat transfer in soils with horizontal, underground and permeable thin layer: Direct and inverse problems

From the dimensionless mathematical model of a scenario 2D, in which heat is transferred from a fluid flow within a thin, horizontal underground layer to the surrounding soil, the dimensionless groups that ruled the solutions are derived. The dependencies of the main unknowns of interest on the parameters of the problem are deduced after the introduction of a characteristic length and time, also assumed as unknowns, for which a constant temperature profile is developed. These dependencies are verified and depicted by universal curves and abacus than can be used in an easy way for the solution of the direct problem in any scenario. The number of dimensionless groups that appear in the solutions are reduced and some of them are collected in the characteristic length and time. In addition, two protocols are proposed for the estimations of flow velocity in the permeable layer from the measurements of experimental temperature profiles, one for the steady state and other for the transient profiles. An illustrative standard application shows the efficiency of such protocols.

Robust calibration and evaluation of a percolation-based effective‐medium approximation model for thermal conductivity of unsaturated soils

Thermal conductivity (λ) is a property characterizing heat transfer in porous media, such as soils and rocks, with broad applications to geothermal systems and aquifer characterizations. Numerous empirical and physically-based models have been developed for thermal conductivity in unsaturated soils. Recently, Ghanbarian and Daigle (G&D) proposed a theoretical model using the percolation-based effective-medium approximation. An explicit form of the G&D model relating λ to water content (θ) and equations to estimate the model parameters were also derived. In this study, we calibrated the G&D model and two widely applied empirical λ(θ) models using a robust calibration dataset of 41 soils. All three λ(θ) model performances were evaluated using a validation dataset of 58 soils. After calibration, the root mean square error (RMSE), mean absolute error (MAE) and coefficient of determination (R2) of the G&D model were 0.092 W−1 m−1 K−1, 0.067 W−1 m−1 K−1 and 0.97, respectively. For the two empirical models, RMSEs ranged from 0.086 to 0.096 W−1 m−1 K−1, MAEs from 0.063 to 0.071 W−1 m−1 K−1, and R2 values were about 0.97. All three metrics indicated that calibration improved the performance of the G&D model, and it had an accuracy similar to that of the two empirical λ(θ) models. Such a robust performance confirmed that the theoretically-based G&D model can be applied to study soil heat transfer and potentially other related fields.

Impacts of seasonally frozen soil hydrothermal dynamics on the watershed hydrological processes inferred from a spatially distributed numerical modelling approach

The freeze–thaw cycle over the surface seasonally frozen soil is an important soil hydrothermal dynamic process linking land surface processes and climatic changes in the cold regions. With the advancement of frozen soil hydrothermal dynamic studies and remote sensing technology, the simulation of frozen soil hydrological processes based on the distributed numerical model has become a hotspot to better understand the impact of frozen soil hydrothermal dynamics on the watershed hydrological processes in the cold regions over a large spatial scale. However, the quantitative analysis of the impact of seasonally frozen soil hydrothermal processes on watershed runoff at long-term time scales remained an unsolved issue in the field of frozen soil hydrology. Under the framework of the watershed distributed eco-hydrological model ESSI-3, a fully distributed frozen soil hydro-thermal processes integrated modeling system (FFIMS model) was established based on the coupled water and heat transferring mechanism for frozen soil hydro-thermal process simulations in the frozen surface or at a certain depth of a watershed. By coupling the FFIMS model with the distributed eco-hydrological model ESSI-3, the impacts of seasonally frozen soil hydrothermal processes on hydrological processes were investigated from the perspective of temporal-spatial domain with the simulated hydrothermal and hydrological processes for a long-term period from 2008 to 2016 over a watershed located in the cold region of Northeastern China. The results suggested that the soil freeze–thaw cycling posed different impacts with limited significance throughout the whole hydrological processes of the watershed in different seasons. Significant impacts on the hydrological processes were particularly observed in the thawing period of a year, when soil ice meltwater contributing to the discharge of the study watershed reached to about 35% in average in this period. ESSI-3 coupled with the FFIMS modelling system obviously improved the performance of the original ESSI-3 in cold region watershed simulations, and the averaged Nash efficiency coefficients obtained increased from almost 0 to 0.77 in the thawing period of a year. The study demonstrated the importance of application of spatially distributed numerical model with physical mechanism for seasonally frozen soil water and heat transfer process simulations.

Unraveling the significance of soil organic carbon-gravel parameterization: Insights into soil water and heat transport on the Tibetan Plateau

In the Tibetan Plateau (TP) soil water and heat transfer process, soil organic carbon (SOC) and gravel content are considered as the most influential soil texture factors. However, the issues of underestimating SOC and neglecting gravel effect affected the simulation performance of CLM5.0 on soil moisture (SM) and soil temperature (ST). This paper proposed a new parameterization scheme, the organic carbon-gravel (OC-G) scheme, to simulate ST and SM from 1990 to 2018. The results showed that correlation between the simulated and observed ST or SM was higher, and the error was smaller, after the modification of the parameterization scheme. This improvement justifies the applicability of the scheme for soil hydrothermal simulations on the TP. The experiment described that ST and SM were more sensitive to changes in SOC content. And changes in gravel or SOC content had the “Same-Frequency” effect in the northeast and southeast TP. When the SOC and gravel content changed at the same time, the effects on ST and SM were a “cumulative” effect. The change directly affected the memory time of ST and SM in summer. Specifically, when the SOC content was increased, the memory time of SM increased in the northwest and decreased in the southeast. When gravel content was increased, the memory time of SM decreased in the northwest but increased in the southeast, but the memory time of ST remained largely unchanged. Changes to the abnormal duration may alter summer weather and climate in Eastern China.