Shallow Subsurface Soil Research Articles

Forest catchment structure mediates shallow subsurface flow and soil base cation fluxes

Hydrologic behavior and soil properties across forested landscapes with complex topography exhibit high variability. The interaction of groundwater with spatially distinct soils produces and transports solutes across catchments, however, the spatiotemporal relationships between groundwater dynamics and soil solute fluxes are difficult to directly evaluate. While whole-catchment export of solutes by shallow subsurface flow represents an integration of soil environments and conditions but many studies compartmentalize soil solute fluxes as hillslope vs. riparian, deep vs. shallow, or as individual soil horizon contributions. This potentially obscures and underestimates the hillslope variation and magnitude of solute fluxes and soil development across the landscape. This study determined the spatial variation and of shallow soil base cation fluxes associated with weathering reactions (Ca, Mg, and Na), soil elemental depletion, and soil saturation dynamics in upland soils within a small, forested watershed at the Hubbard Brook Experimental Forest, NH. Base cation fluxes were calculated using a combination of ion-exchange resins placed in shallow groundwater wells (0.3 – 1 m depth) located across hillslope transects (ridges to lower backslopes) and measurements of groundwater levels. Groundwater levels were also used to create metrics of annual soil saturation. Base cation fluxes were positively correlated with soil saturation frequency and were greatest in soil profiles where primary minerals were most depleted of base cations (i.e., highly weathered). Spatial differences in soil saturation across the catchment were strongly related to topographic properties of the upslope drainage area and are interpreted to result from spatial variations in transient groundwater dynamics. Results from this work suggest that the structure of a catchment defines the spatial architecture of base cation fluxes, likely reflecting the mediation of subsurface stormflow dynamics on soil development. Furthermore, this work highlights the importance of further compartmentalizing solute fluxes along hillslopes, where certain areas may disproportionately contribute solutes to the whole catchment. Refining catchment controls on base cation generation and transport could be an important tool for opening the black box of catchment elemental cycling.

Understanding the impact of flow mechanisms in unsaturated layer on heat transfer near a partially submerged geothermal heat exchanger

Heat transfer near geothermal heat exchangers in the presence of groundwater flow has been extensively studied over the past years. However, previous studies often overlooked the presence of an unsaturated layer in the shallow subsurface soil, or disregarded phase change and fluid flow within this layer. In this study, a comprehensive hydro-thermal model is developed to evaluate heat transfer near a partially submerged geothermal borehole in groundwater flow while incorporating phase change and liquid and vapor flow in the unsaturated layer. The effect of unsaturated soil hydraulic analysis on heat transfer and energy efficiency of the geothermal piles is explored under varying soil permeabilities, air-entry suctions, solid thermal conductivities, and soil types. Consideration of water content variation and unsaturated fluid flow in the model enhances heat injection rate by up to 11.23 % in highly permeable soils. However, in scenarios with higher solid thermal conductivity, or lower air-entry suction values, the heat injection rate reduces by as much as 16.13 % due to unsaturated soil hydraulic analysis. Furthermore, it is found that consideration of unsaturated soil hydraulic analysis is of greater importance in Bonny silt than sandy soil, lowering the heat injection rate by 8.53 % and 2.53 %, respectively.

Investigation of Lunar Shallow Subsurface Water Content and Soil Elemental Composition via Active Neutron Detection

The detection of planetary water and soil elements is a pivotal area of research due to its implications for understanding celestial bodies. Within the realm of planetary sampling missions, attention is predominantly directed toward the shallow surface layers, typically to a depth of 1 m. This paper examines the Moon as a case study, employing Monte Carlo simulations to introduce an active detection methodology that integrates high-energy neutron pulse generators with neutron and gamma detectors. Simulations were made of the albedo neutrons and prompt gamma counts after mitigating the interference of secondary neutrons and gamma rays, which result from the interaction between galactic cosmic rays and the lunar surface. The depth limit of active neutron detection on the shallow surface is about 100 cm. The cadmium ratio (CdR), the ratio between total neutron counts and counts caused by nonthermal neutrons, facilitates the rapid and accurate water content calculation using a fitted CdR curve. Standard gamma spectra of the associated elements, derived through Monte Carlo simulations, along with the mixed gamma spectra requiring resolution, form the foundation for the spectral analysis. Utilizing the weighted least-squares method to invert gamma spectra facilitates the identification of the content of associated elements. Integrating the analysis of albedo neutron energy spectra with prompt gamma spectra allows for the rapid assessment of the region’s water content and soil conditions. Moreover, this study also explores the impact of variations in the content of associated elements on the determination of water content.

Modeled Forest Conversion Influences Humid Tropical Watershed Hydrology More than Projected Climate Change

In the humid tropics, forest conversion and climate change threaten the hydrological function and stationarity of watersheds, particularly in steep terrain. As climate change intensifies, shifting precipitation patterns and expanding agricultural and pastoral land use may effectively reduce the resilience of headwater catchments. Compounding this problem is the limited long-term monitoring in developing countries for planning in an uncertain future. In this study, we asked which change, climate or land use, more greatly affects stream discharge in humid tropical mountain watersheds? To answer this question, we used the process-based, spatially distributed Soil Moisture Routing model. After first evaluating model performance (Ns = 0.73), we conducted a global sensitivity analysis to identify the model parameters that most strongly influence simulated watershed discharge. In particular, peak flows are most influenced by input model parameters that represent shallow subsurface soil pathways and saturation-excess runoff while low flows are most sensitive to macropore hydraulic conductivity, soil depth and porosity parameters. We then simulated a range of land use and climate scenarios in three mountain watersheds of central Costa Rica. Our results show that deforestation influences streamflow more than altered precipitation and temperature patterns through changes in first-order hydrologic hillslope processes. However, forest conversion coupled with intensifying precipitation events amplifies hydrological extremes, reducing the hydrological resilience to predicted climate shifts in mountain watersheds of the humid tropics. This finding suggests that reforestation can help mitigate the effects of climate change on streamflow dynamics in the tropics including impacts to water availability, flood pulses, channel geomorphology and aquatic habitat associated with altered flow regimes.

Investigation of shallow subsurface soil for engineering construction: A case study of Etioro Akoko, Southwestern Nigeria

For sustainable development of Etioro Akoko, Southwestern Nigeria, soil materials must meet and exceed the requirements of a good tropical environment soil. This study is aimed at using geotechnical and geophysical investigations to evaluate the subsoil for pre- and post-engineering construction and to achieve sustainable groundwater development. The geotechnical analyses are grain size analysis, Atterberg, linear shrinkage, specific gravity, CBR and compaction tests, while electrical resistivity method was used for geophysical investigation. The geotechnical analysis of liquid limit, plastic limit, plasticity index, linear shrinkage, grain size analysis, specific gravity, CBR and compaction tests range from 24.0%–40.8%, 19.3%–23.7%, 4.3%–17.4%, 1.4%–9.3%, 2.58–2.62, 30%–46%, 1496 kg/m3–1742 kg/m3 and 10%–14.2%, respectively. For the electrical resistivity approach, six traverses in an east–west orientation were created. Four distinct layers were identified, and they are top soil, weathered layer, slightly weathered layer and bedrock. Two wells of moderate to good yield were identified from the different fractures located. Atterberg limit tests and grain size analysis of the soil samples showed that these soil samples met the requirements for a good soil in Nigeria. The CBR and MDD values showed that they are suitable for subgrade courses. We reject the null hypothesis for statistical analysis between the mean resistivity values of the six traverses and the geotechnical properties of the soil and also the ANOVA statistic between resistivity values and the six traverses, while we accept the null hypothesis for variables between geotechnical data.

Long-term Thermo-hydraulic Response of the Shallow Subsurface soil in the Vicinity of a Buried Horizontal Heat Source

Heat and mass transfer in the shallow subsurface and in the vicinity of buried heat sources has been often studied based on rather simplifying assumptions, such as the Equilibrium Phase Change (EPC), disregarding film flow, and adsorptive soil-water characteristics. In this study, a fully coupled non-isothermal multiphase flow model is developed that utilizes the Non-equilibrium Phase Change (NEPC) approach. First, the performance of the EPC and NEPC approaches is assessed and validated against the in-field experimental data. The second and main objective of this study is to analyze the thermo-hydraulic response of granular soil close to a buried horizontal heat source (e.g., electrical cables) for one year under real meteorological conditions. Numerical results indicate that the NEPC model has higher robustness in predicting the volumetric water content in the soil close to the soil-atmospheric boundary. However, NEPC and EPC approaches estimate the same temperature variations in the soil. In the case of precipitation (e.g., rainfall), the NEPC model predicts higher degrees of saturation in deeper soil in which the infiltrated water reaches 150 cm below the surface, while, in the EPC model, the infiltrated water barely reaches the 100 cm depth. The increase in moisture content close to the heat source facilitates the heat transfer in the medium and thus results in a 40% to 50% reduction in soil temperature close to the heat source. An accurate prediction of the soil moisture content in the medium is needed to evaluate the performance and thermal capacity of buried electrical cables. Furthermore, the heating/cooling cycles contribute to gradually drying the soil in the vicinity of the heater until the hydraulically equilibrated condition is attained.

Replication Data for: Evaluation of model concepts to describe water transport in shallow subsurface soil and across the soil–air interface

Replication Data for: Evaluation of model concepts to describe water transport in shallow subsurface soil and across the soil–air interface

APPLICATION OF GROUND PENETRATING RADAR (GPR) METHOD FOR THE CHARACTERIZATION OF SOIL NEAR TIARET (NORTH-WEST OF ALGERIA)

The Tiaret-Saida is a new high-speed railway under construction in northwestern Algeria. The main objective of this study is to map the shallow subsurface geological features and soil characterization. A geophysical tool comprising ground penetrating radar (GPR) has been applied for identifying the possible presence of cavities and fractures in the subsoil. GPR measurements were taken from a total of 24 profiles. The total length of the profiles was 240 m. The results of the GPR profiles obtained by two central frequencies 200 and 400 MHz indicate the existence of several anomalies that can be attributed to cavities and fractures in the bottom of several excavations, at depth ranging from 1 to 2.2 m. The interpreted results of GPR data were calibrated with the available lithological data from five boreholes drilled.

Geothermal Energy Use in Western Siberia and Prospects for Its Innovative Application in Construction

The article gives an overview of the use of low-temperature geothermal energy sources for heat and cold supply of buildings in areas of Western Siberia. The experience of using geothermal heat pumps shows their economic efficiency and environmental friendliness. An innovative application of the low-temperature energy of the shallow subsurface soil layers is the double use of the underground foundation of a building or another structure as energy active elements of the heat-pumping system. The paper analyzes the problems why green technologies are not developing as dynamically as indicated in the Energy Program of Russia and barriers that prevent the wider use of heat pumps and systems in the heat and cold supply of buildings in the Siberian region. These include considerable regulatory and investment barriers, as well as lack of awareness about renewable energy and energy efficiency. Further, market entry remains challenging in Russia that has not fully liberalised its energy market. Furthermore, entrenched interests in conventional energy resources represent a significant barrier to effective legislation and policy implementation. Thus, huge conventional resources of oil, gas and coal in Siberia region, neighboring to Novosibirsk, Omsk and Altay districts are other obstacles to the introduction of renewable green technologies. Some examples on the limitation of barriers to geothermal heat pumps systems application in building construction are given.

Utilization of Nonequilibrium Phase Change Approach to Analyze the Nonisothermal Multiphase Flow in Shallow Subsurface Soils

AbstractThe prediction of coupled nonisothermal multiphase flow in porous media has been the subject of many theoretical and experimental studies in the past half a century. In particular, the evaporation phenomenon from the shallow subsurface has been extensively studied based on the notion of equilibrium phase change between liquid water and water vapor (i.e., instantaneous phase change). One of the frequent assumptions in equilibrium phase change approach is that liquid water is hydraulically connected throughout the vadose zone. Furthermore, classical soil‐water retention curves (e.g., van Genuchten model), which have been extensively used in the literature to model evaporation process, are only valid for high and intermediate saturation degrees. Although these limitations have been addressed and improved in separate studies, they have not yet been rigorously incorporated in the numerical modeling of nonisothermal multiphase flow in shallow subsurface of in‐field soils. Therefore, the aim of this study is to investigate the coupled heat, liquid, and vapor flow in soil media through the Hertz‐Knudsen‐Schrage (HKS) phase change model and by incorporating a water retention model which captures the soil‐water characteristics from full to oven‐dried saturation degrees. A numerical model is developed and validated against the in‐field experimental data. Reasonable agreements between the calculated and measured values of water contents at all depths, as well as the temperature, and cumulative evaporation are observed. Results also confirm that the contribution of the film flow in overall mass flow in the medium is required for accurate modeling and cannot be ignored.

Shallow Subsurface Structure in the Hualien Basin and Relevance to the Damage Pattern and Fault Rupture during the 2018 Hualien Earthquake

ABSTRACTThe 2018 Mw 6.4 Hualien earthquake generated a large peak-to-peak velocity of over 2 m/s, with a period of 3 s at the south end of the Milun fault, which resulted in the collapse of five buildings. To investigate the shallow subsurface soil structure and evaluate possible effects on the ground motion and building damage, we performed microtremor measurements in the Hualien basin. Based on the velocity structure jointly inverted from both Rayleigh-wave dispersion curves and microtremor horizontal-to-vertical spectral ratio data, we found that the shallow subsurface structure generally deepens from west to east. Close to the Milun fault, the structure becomes shallower, which is consistent with faulting during the 2018 earthquake and the long-term tectonic displacement. There is no significant variation for the site conditions in the north–south direction that can explain the large peak ground velocity in the south. As a result of the dense measurements in the heavily damaged area, where three high-rise buildings totally collapsed, these locations have the average S-wave velocity of the upper 30 m (AVS30) values and are relatively high compared to the more distant area from the Meilun River. This is somewhat unusual, because lower AVS30 values indicating softer ground conditions are expected close to the river. We did not find any characteristic subsurface soil structure that may contribute to the building collapses. The large 3 s pulse was probably generated by source effects, rather than subsurface soil amplification.

Geophysical and geotechnical characterization of shallow subsurface soil: a case study of University of Peshawar and surrounding areas

The proper design and successful construction of engineered structures require determination of the engineering properties of the soil. These properties, however, are conventionally determined in the laboratory using soil samples collected from the construction site. The collection of soil samples is generally an expensive and time-consuming activity, while the extraction of an undisturbed soil sample is difficult. Furthermore, there are wide variations in the temporal and spatial properties of soil and their accurate evaluation requires high-density sampling. Recently, electric resistivity surveying has attracted much attention. It is commonly applied in the analysis of engineering sites, as it is rapid, cost-effective, and non-destructive. Based on this hypothesis, electrical resistivity was measured at four boreholes in the areas surrounding the University of Peshawar using standard methods of resistivity survey, i.e., Schlumberger electrode configuration. The resistivity data that was obtained by vertical electrical sounding (VES) from the fieldwork was correlated with geotechnical data obtained through the analysis of soil samples in the laboratory. Electrical resistivity had an inverse relationship with gravimetric moisture content and cohesion, with the highest regression coefficients observed in the case of GYM-UAP and Girls’ Hostel-UAP (R2 = 0.97 and 0.96) boreholes, respectively. Moreover, electrical resistivity had a significant linear correlation with the angle of internal friction and standard penetration test-N (SPT-N) values, with the highest regression coefficient of GYM-UAP (R2 = 0.99) and Girls’ Hostel-UAP (R2 = 0.95), respectively. In conclusion, the obtained relationships between electrical resistivity and different geotechnical properties could be adopted for the assessment of geotechnical properties of soils, especially when many samples are difficult to obtain.

Water harvesting from soils by light-to-heat induced evaporation and capillary water migration

Freshwater scarcity is one of the critical challenges for global sustainable development. Several novel water resources, such as passive seawater solar desalination and atmospheric water harvesting, have made some progress in recent years. However, no investigation has referred to harvesting water from shallow subsurface soils, which are potential huge water reservoirs. Here, we introduce a method of light-driven water harvesting from soils, which can provide cheap freshwater of very high quality in impoverished, arid, and decentralized areas. Concentrated solar energy is used to heat the soils to evaporate the soil moisture. Then vapors flow to the condenser through tubes and condense as freshwater. Sustainable water harvesting is realized by water migration due to the capillary pumping effect within soils. In the laboratory conditions, an experimental setup was designed and its water-harvesting ability from soils was investigated. The maximum water mass harvesting rate was 99.8 g h−1. Considering the dimensions of the samples, the maximum water harvesting rate per cubic meter of the samples could be recalculated to be about 12.0 kg h−1 m−3. In about 12 h, the total harvesting water could be as high as about 900 ml. The energy efficiency of our method was also estimated to be about 2.6–21.6%, depending on the heating powers and soil water contents. Then the water harvesting rate of one sun energy flux (1 kW m−2) was estimated to be approximately 360 g h−1 with a 1 m2 solar concentrator. Furthermore, the testing results of the water quality indicate that the collected water was high-quality drinking water. Our proposal provides a potential onsite and sustainable freshwater supply solution to deal with the water scarcity problem in impoverished, arid, and coastal regions after natural disasters.

Monitoring Freeze-Thaw State by Means of GNSS Reflectometry: An Analysis of TechDemoSat-1 Data

The article of the freeze/thaw dynamic of high-latitude Earth surfaces is extremely important and informative for monitoring the carbon cycle, the climate change, and the security of infrastructures. Current methodologies mainly rely on the use of active and passive microwave sensors, while very few efforts have been devoted to the assessment of the potential of observations based on signals of opportunity. This article aims at assessing the performance of spaceborne Global Navigation Satellite System Reflectometry (GNSS-R) for high-spatial and high-temporal resolution monitoring of the Earth-surface freeze/thaw state. To this aim, reflectivity values derived from the TechDemoSat-1 (TDS-1) data have been collected and elaborated, and thus compared against the soil moisture active passive (SMAP) freeze/thaw information. Shallow subsurface soil temperature values recorded by a network of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> stations have been considered as well. Even if an extensive and timeliness cross availability of both types of experimental data is limited by the spatial coverage and density of TDS-1 observations, the proposed analysis clearly indicates a significant seasonal cycle in the calibrated reflectivity. This opens new perspectives for the bistatic L-band high-resolution satellite monitoring of the freeze/thaw state, as well as to support the development of next-generation of GNSS-R satellite missions designed to provide enhanced performance and improved temporal and spatial coverage over high latitude areas.

Evaluation of Model Concepts to Describe Water Transport in Shallow Subsurface Soil and Across the Soil\u2013Air Interface

Soil water evaporation plays a critical role in mass and energy exchanges across the land–atmosphere interface. Although much is known about this process, there is no agreement on the best modeling approaches to determine soil water evaporation due to the complexity of the numerical modeling scenarios and lack of experimental data available to validate such models. Existing studies show numerical and experimental discrepancies in the evaporation behavior and soil water distribution in soils at various scales, driving us to revisit the key process representation in subsurface soil. Therefore, the goal of this work is to test different mathematical formulations used to estimate evaporation from bare soils to critically evaluate the model formulations, assumptions and surface boundary conditions. This comparison required the development of three numerical models at the REV scale that vary in their complexity in characterizing water flow and evaporation, using the same modeling platform. The performance of the models was evaluated by comparing with experimental data generated from a soil tank/boundary layer wind tunnel experimental apparatus equipped with a sensor network to continuously monitor water–temperature–humidity variables. A series of experiments were performed in which the soil tank was packed with different soil types. Results demonstrate that the approaches vary in their ability to capture different stages of evaporation and no one approach can be deemed most appropriate for every scenario. When a proper top boundary condition and space discretization are defined, the Richards equation-based models (Richards model and Richards vapor model) can generally capture the evaporation behaviors across the entire range of soil saturations, comparing well with the experimental data. The simulation results of the non-equilibrium two-component two-phase model which considers vapor transport as an independent process generally agree well with the observations in terms of evaporation behavior and soil water dynamics. Certain differences in simulation results can be observed between equilibrium and non-equilibrium approaches. Comparisons of the models and the boundary layer formulations highlight the need to revisit key assumptions that influence evaporation behavior, highlighting the need to further understand water and vapor transport processes in soil to improve model accuracy.

IMARS Phase 2A Draft Mission Architecture and Science Management Plan for the Return of Samples from Mars Phase 2 Report of the International Mars Architecture for the Return of Samples (iMARS) Working Group.

iMARS Phase 2A Draft Mission Architecture and Science Management Plan for the Return of Samples from Mars Phase 2 Report of the International Mars Architecture for the Return of Samples (iMARS) Working Group.

Integration of Magnetic and Geotechnical methods for Shallow Subsurface Soil Characterization at Sungai Batu, Kedah, Malaysia

Magnetic and geotechnical methods were used for shallow subsurface soil characterization at Sungai Batu, Kedah, (Malaysia). Ground magnetic data were collected along a survey line of length 160 m long at 2 m constant station spacing, while soil drilling using hand auger was conducted at 21 m on the survey line using 0.2 m sampling interval drilled to a depth of 5 m. Result from the processed magnetic profile data shows distribution of magnetic residuals in the range of -4.55 to 1.61 nT, with magnetic low (-4.55 nT to -0.058 nT) and were identified at distances 4 m, 10 to 16 m, 20 to 26 m, 58 m, 82 m, 104 to 106 m, 118 m, and 124 to 140 m. The magnetic lows are attributes of sediments. The result from the soil drilling shows sticky samples with variable sizes, greyish to brownish / reddish in colour, and some of the samples show the presence of shiny and black spots. The characteristics of the samples suggest the soil as a by-product of completely weathered rock; weak with high water content and classified as Grade V soil. The study concludes; integration of geophysical and geotechnical methods aided in characterizing the subsurface soil at Sungai Batu. The result was correlated with previous studies and confirms the importance of integrated approach in minimising ambiguity in interpretation.

A Global Gridded Dataset of GRACE Drought Severity Index for 2002–14: Comparison with PDSI and SPEI and a Case Study of the Australia Millennium Drought

Abstract A new monthly global drought severity index (DSI) dataset developed from satellite-observed time-variable terrestrial water storage changes from the Gravity Recovery and Climate Experiment (GRACE) is presented. The GRACE-DSI record spans from 2002 to 2014 and will be extended with the ongoing GRACE and scheduled GRACE Follow-On missions. The GRACE-DSI captures major global drought events during the past decade and shows overall favorable spatiotemporal agreement with other commonly used drought metrics, including the Palmer drought severity index (PDSI) and the standardized precipitation evapotranspiration index (SPEI). The assets of the GRACE-DSI are 1) that it is based solely on satellite gravimetric observations and thus provides globally consistent drought monitoring, particularly where sparse ground observations (especially precipitation) constrain the use of traditional model-based monitoring methods; 2) that it has a large footprint (~350 km), so it is suitable for assessing regional- and global-scale drought; and 3) that it is sensitive to the overall terrestrial water storage component of the hydrologic cycle and therefore complements existing drought monitoring datasets by providing information about groundwater storage changes, which affect soil moisture recharge and drought recovery. In Australia, it is demonstrated that combining GRACE-DSI with other satellite environmental datasets improves the characterization of the 2000s “Millennium Drought” at shallow surface and subsurface soil layers. Contrasting vegetation greenness response to surface and underground water supply changes between western and eastern Australia is found, which might indicate that these regions have different relative plant rooting depths.

Slope Stability Analysis through Integration of Ground Measurements and Remote Sensing Data

Slope failures and shallow landslides occur due to shallow subsurface flow convergence, soil saturation and shear strength reduction following a heavy rainfall. The semi-arid environment of southern Arizona (AZ) experiences a significant increase in precipitation during the summer. As a result, the soil moisture increases the potential for slope failure due to water table fluctuation and pore pressure escalation. In this paper, the relationship between soil moisture distribution and topography information (slope angle, topography wetness index) is examined using the topography wetness index, NASA's Shuttle Radar Topography Mission (SRTM) images and cokriging. Using the Digital Elevation Model (DEM) generated from remote sensing images, the slope stability analysis is performed in a typical semi-arid environment area using data from the Waternut Gulch Experimental Watershed in Tombstone, AZ. Conclusions and future research are provided at the end of the paper.

Attribution of precipitation changes on ground–air temperature offset: Granger causality analysis

This work examines the causal relationship between the value of the ground–air temperature offset and the precipitation changes for monitored 5-min data series together with their hourly and daily averages obtained at the Sporilov Geophysical Observatory (Prague). Shallow subsurface soil temperatures were monitored under four different land cover types (bare soil, sand, short-cut grass and asphalt). The ground surface temperature (GST) and surface air temperature (SAT) offset, ΔT(GST–SAT), is defined as the difference between the temperature measured at the depth of 2 cm below the surface and the air temperature measured at 5 cm above the surface. The results of the Granger causality test did not reveal any evidence of Granger causality for precipitation to ground–air temperature offsets on the daily scale of aggregation except for the asphalt pavement. On the contrary, a strong evidence of Granger causality for precipitation to the ground–air temperature offsets was found on the hourly scale of aggregation for all land cover types except for the sand surface cover. All results are sensitive to the lag choice of the autoregressive model. On the whole, obtained results contain valuable information on the delay time of ΔT(GST–SAT) caused by the rainfall events and confirmed the importance of using autoregressive models to understand the ground–air temperature relationship.