Soil Temperature Profiles Research Articles

The Amazon Tall Tower Observatory (ATTO): overview of pilot measurements on ecosystem ecology, meteorology, trace gases, and aerosols

Abstract. The Amazon Basin plays key roles in the carbon and water cycles, climate change, atmospheric chemistry, and biodiversity. It has already been changed significantly by human activities, and more pervasive change is expected to occur in the coming decades. It is therefore essential to establish long-term measurement sites that provide a baseline record of present-day climatic, biogeochemical, and atmospheric conditions and that will be operated over coming decades to monitor change in the Amazon region, as human perturbations increase in the future. The Amazon Tall Tower Observatory (ATTO) has been set up in a pristine rain forest region in the central Amazon Basin, about 150 km northeast of the city of Manaus. Two 80 m towers have been operated at the site since 2012, and a 325 m tower is nearing completion in mid-2015. An ecological survey including a biodiversity assessment has been conducted in the forest region surrounding the site. Measurements of micrometeorological and atmospheric chemical variables were initiated in 2012, and their range has continued to broaden over the last few years. The meteorological and micrometeorological measurements include temperature and wind profiles, precipitation, water and energy fluxes, turbulence components, soil temperature profiles and soil heat fluxes, radiation fluxes, and visibility. A tree has been instrumented to measure stem profiles of temperature, light intensity, and water content in cryptogamic covers. The trace gas measurements comprise continuous monitoring of carbon dioxide, carbon monoxide, methane, and ozone at five to eight different heights, complemented by a variety of additional species measured during intensive campaigns (e.g., VOC, NO, NO2, and OH reactivity). Aerosol optical, microphysical, and chemical measurements are being made above the canopy as well as in the canopy space. They include aerosol light scattering and absorption, fluorescence, number and volume size distributions, chemical composition, cloud condensation nuclei (CCN) concentrations, and hygroscopicity. In this paper, we discuss the scientific context of the ATTO observatory and present an overview of results from ecological, meteorological, and chemical pilot studies at the ATTO site.

A parametrization of a steady periodic solution of the Fourier equation to model soil temperature dynamics

AbstractIn dry days the temperature of the upper soil layers presents a characteristic asymmetric periodic‐like pattern with a minimum in the morning and a maximum in the afternoon. In view of estimating the conductive heat component of the surface energy balance, at local, basin, and global scales, in this study we use a periodic series solution of the Fourier equation to develop a simple procedure to accurately reconstruct the soil temperature and heat flux profiles. The method is based on weighting and phasing the Fourier harmonics by means of coefficients which do not depend on the soil thermal properties but only depend on the shape of the temperature boundary condition. The proposed coefficients can be regarded to as site independent and with good approximation universal. In order to calibrate and test the procedure, measurements of soil temperature, soil heat flux, and soil water content, collected during the CividatEX Experiment (summer 2012, summer 2013, and spring and summer 2014), in Italy, were used. The method accurately reproduced the temperature observations at three measurement depths within the upper 20 cm soil layer. Once assessed the soil thermal conductivity, the method proved to be effective also in reproducing the measured soil heat flux. The procedure was furthermore validated reconstructing with good results the soil temperature dynamics measured by an independent micrometeorological station in a different environment.

The Sap Flow Dynamics and Response of Hedysarum scoparium to Environmental Factors in Semiarid Northwestern China.

Hedysarum scoparium is an important, fast-growing and drought-resistant shrub that has been extensively used for grassland restoration and preventing desertification in semiarid regions of northwestern China. The primary objective of this study was to investigate the diurnal and seasonal variations in stem sap flow (J s) and its relation to environmental factors. The stem heat balance method was applied to plants that were approximately 17 years old (with diameters of 25, 16, 13, and 9 mm at ground level and heights of 3.1, 1.8, 1.7 and 1.4 m) and growing under natural conditions. The vertical soil temperature profile (ST), soil surface heat flux (SoilG), volumetric soil moisture content (SWC) and meteorological variables such as solar radiation (R n), air temperature (T a), vapour pressure deficit (VPD), wind speed (W s) relative humidity (RH) and precipitation (P) were simultaneously measured at a meteorological station on site. Results indicated that J s varied regularly during the diurnal and seasonal term. The nocturnal J s was substantial, with a seasonal variation similar to the patterns of daytime J s. The magnitude of J s changed considerably between sunny and rainy days. Redundancy (RDA) and Kendall’s tau analysis suggested that daily J s in large plants was more sensitive to environmental factors, and the variation in daily J s during the growing season could be described by a multiple linear regression against environmental variables including T a, VPD, W s, RH, ST, and SoilG. While the nocturnal J s in smaller plants was more sensitive to meteorological factors. T a, VPD, and W s were significantly correlated with nighttime J s. The hourly nighttime sap flow rate of H. scoparium corresponded closely to T a and VPD following a non-linear pattern. The results of this study can be used to estimate the transpiration of H. scoparium.

Temporal Variations in the Surface Soil Heat Flux over Maize and Grass Surfaces in Northwest China

Surface soil heat flux (G(0)) is an indispensable component of the surface energy balance (SEB) and is important for estimating instantaneous surface evapotranspiration (ET). Many studies suggest that daily or longer timescales of G(0) can be ignored, whereas other studies suggest the opposite. In this study, a long-term G(0) was calculated using a heat conduction equation based on observed soil temperature and moisture profiles over 30-min intervals from January 2008 to December 2011. Maize and meadows covered the study area in the Heihe River Basin (HRB), northwestern China. The effects of various timescales of G(0) (half-hourly, daily, monthly, and yearly) on energy balance closure (EBC) and ET estimations were quantitatively analyzed. The results showed that the diurnal G(0) had the same magnitude as the sensible heat flux, and it increased the EBC by 12.9 and 8.2% in maize and grasslands, respectively. The maximum daily G(0) reached 20% of the net radiation, and the maximum monthly ET was overestimated by 15% when neglecting the monthly G(0) over the bare soil when the maize has not germinated. The yearly G(0) values were nearly zero in maize and grasslands and were excluded. Thus, the G(0) is important for EBC and ET estimation with shorter timescale than annual timescale. The G(0) should not be neglected except for annual timescale.

Seasonal Thermal Ecology of Bog Turtles (Glyptemys muhlenbergii) in Southwestern Virginia

Abstract Aquatic and semiaquatic turtles use wetlands and thermally buffered soils to thermoregulate during the active season and to sustain body temperatures above freezing during overwintering. We deployed temperature data loggers during wintertime and summertime in wetlands occupied by Bog Turtles (Glyptemys muhlenbergii) in southwestern Virginia, United States, to contrast the temperatures of the wetland environment to turtle carapace temperatures over two field seasons. Temperature signatures were used to evaluate probable hibernation depth and the timing and cues of spring emergence. We measured soil temperature profiles during winter in saturated hibernacula and similar but unsaturated structures to evaluate the dependence of temperature on water-table depth. Mean daily turtle temperature (n = 16) during the coldest portion of two winters was 2.5°C (SE = 0.29), with one turtle experiencing 14 continuous days at temperatures between −1°C and 0°C when ambient temperatures dipped below −10°C. Water ta...

Climatic Effects on In-Situ Soil State Profiles Considering a Coupled Soil-Atmosphere Interaction Model

The influence of soil-atmosphere interactions on an unsaturated soil in water-limited environment is investigated using a coupled heat-water flow model with a balance of net solar energy at earth’s surface. The paper also presents the governing equations for soil-atmosphere interaction analysis which, although important, are still rare in geotechnical applications. Numerical results were obtained by approximating the governing partial differential equations through a 1D finite difference scheme representing the soil as a two-layer system. Soil state profiles (temperature, moisture and suction) were predicted using daily meteorological data collected in France, from 2004 to 2005. Parametric analyses estimated the effects on soil state profiles caused by changes in initial conditions (soil temperature), hydraulic properties (saturated hydraulic conductivity), model geometry (upper layer thickness), ratio of reflected to incident solar radiation (soil albedo) and characteristics of meteorological data (sampling frequency). For the investigated site, the zone of seasonal fluctuations (ZSF) where the moisture and corresponding suction profiles is influenced by climatic conditions is about 1.5 m. The results also show that calculated average month meteorological values as daily inputs modify significantly the ZSF (about 100%). Predicted soil temperature profiles were in good agreement with measured values.

An improved algorithm to estimate the surface soil heat flux over a heterogeneous surface: A case study in the Heihe River Basin

Surface soil heat flux (G0) is an indispensable component of the surface energy balance and plays an important role in the estimation of surface evapotranspiration (ET). This study calculated G0 in the Heihe River Basin based on the thermal diffusion equation, using the observed soil temperature and moisture profiles, with the aim to analyze the spatial-temporal variations of G0 over the heterogeneous area (with alpine grassland, farmland, and forest). The soil ice content was estimated by the difference in liquid soil water content before and after the melting of the frozen soil and its impact on the calculation of G0 was further analyzed. The results show that: (1) the diurnal variation of G0 is obvious under different underlying surfaces in the Heihe River Basin, and the time when the daily maximum value of G0 occurs is a few minutes to several hours earlier than that of the net radiation flux, which is related to the soil texture, soil moisture, soil thermal properties, and the vegetation coverage; (2) the net radiation flux varies with season and reaches the maximum in summer and the minimum in winter, whereas G0 reaches the maximum in spring rather than in summer, because more vegetation in summer hinders energy transfer into the soil; (3) the proportions of G0 to the net radiation flux are different with seasons and surface types, and the mean values in January are 25.6% at the Arou site, 22.9% at the Yingke site and 4.3% at the Guantan site, whereas the values in July are 2.3%, 1.6% and 0.3%, respectively; and (4) G0 increases when the soil ice content is included in thermal diffusion equation, which improves the surface energy balance closure by 4.3%.

Remediation of hydrocarbon polluted soils using 2.45 GHz frequency-heating: Influence of operating power and soil texture on soil temperature profiles and contaminant removal kinetics

2.45GHz frequency heating treatment of diesel-contaminated soils was applied to investigate the effects of operating power and soil texture on soil temperature profiles and contaminant removal kinetics. Four soil size aggregate fractions, corresponding to medium (200–350μm) and fine (75–200μm) sand, silt (10–75μm) and clay (<4μm) were artificially contaminated with diesel fuel and remediated with lab-scale apparatus for different lengths of time. Results suggest that soil texture significantly influences the contaminant removal kinetics and that thermodynamic and dielectric properties of soils have a major effect on the final temperature reachable during the heating processes. Minimal contaminant residual concentrations (<400mgkg−1) were achievable only for sandy soils, for which the highest contaminant removals (>90%) were reached. The power low kinetic model showed a quite good correlation (r2>0.976) with the experimental data for residual concentration at all operating powers and for all soils investigated. Contaminant rate decay (k) variation observed for the different soils indicates that contaminant removal processes strictly depend both on thermal properties and specific surface area of soil regulating the adsorption–desorption phenomena related to the decontamination treatment. Especially for sandy soils, microwave heat treatment could be a better choice for remediation of diesel polluted soils compared to several other biological, chemical–physical or conventional thermal treatments due to its removal efficiency.

Effects of autumn tillage and residue management on soil respiration in a long‐term field experiment in Sweden

AbstractSeveral previous field studies in temperate regions have shown decreased soil respiration after conventional tillage compared with reduced or no‐tillage treatments. Whether this decrease is due to differences in plant residue distribution or changes in soil structure following tillage remains an open question. This study investigated (1) the effects of residue management and incorporation depth on soil respiration and (2) biological activity in different post‐tillage aggregates representing the actual size and distribution of aggregates observed in the tilled layer. The study was conducted within a long‐term tillage experiment on a clay soil (Eutric Cambisol) in Uppsala, Sweden. After 38 y, four replicate plots in two long‐term treatments (moldboard plowing (MP) and shallow tillage (ST)) were split into three subplots. These were then used for a short‐term trial in which crop residues were either removed, left on the surface or incorporated to about 6 cm depth (ST) or at 20 cm depth (MP). Soil respiration, soil temperature, and water content were monitored during a 10‐d period after tillage treatment. Respiration from aggregates of different sizes produced by ST and MP was also measured at constant water potential and temperature in the laboratory. The results showed that MP decreased short‐term soil respiration compared with ST or no tillage. Small aggregates (&lt; 16 mm) were biologically most active, irrespective of tillage method, but due to their low proportion of total soil mass they contributed &lt; 1.5% to total respiration from the tilled layer. Differences in respiration between tillage treatments were found to be attributable to indirect effects on soil moisture and temperature profiles and the depth distribution of crop residues, rather than to physical disturbance of the soil.

Ground ice and hydrothermal ground motions on aufeis plots of river valleys

Localized groundwater outflow and layered freezing of them in forms of large ice clusters on the surface creates specific conditions for energy and mass exchange in the «atmosphere–soil–lithosphere» system. In winter, the soil temperature profile is essentially deformed due to heat emission by the aufeis layer of water at its freezing that forms a specific thermocline layer. Deformation of the temperature profile, gradually decreasing, moves down the cross - section and disappearing at the interface between frozen and thawed rocks. Magnitude and number of the temperature deviations from a «normal» state depends on the heat storage of the aufeis - forming waters and on the number of outflows at a given point. The thermocline formation changes conditions of freezing for underlying ground layers together with mechanism of ice saturation of them, and that results in formation of two - layer ice - ground complexes (IGC) which differ drastically from cryogenic features in adjacent parts of the valley. Analysis of genetic characteristics and relation of components of the surface and subsurface layers allowed identification of seven types of the aufeis IGC: massive - segregation, cement - basal, layered - segregation, basal - segregation, vacuum - filtration, pressureinjection, and fissure - vein. Yearly formation and destruction of aufeises and subsurface ices is accompanied by a sequence of particularly hazardous geodynamical phenomena, among which the most important are winter flooding of territories, layered freezing of water, ground heaving, thermokarst, and thermoerosion. Combination of these processes may cause a rapid (often unexpected) reconfiguration of channels of both surface and subsurface runoff, abrupt uplifts and subsidences of the surface, and decompaction and «shaking - up» of seasonally thawing and seasonally freezing rocks, which may create exceptionally unfavorable conditions for construction and operation of engineering structures. Aufeis plots of river valleys are the most «hot» points of the permafrost zone. A comprehensive study of them requires organization of several reference aufeis test areas located in different natural - climatic and geocryological zones. In addition to the natural - historical and methodological aspects, the future research program should include consideration of problems related to interaction between engineering structures and aufeis events and aufeis ice - ground complexes.

Analytical Solutions for Ground Temperature Profiles and Stored Energy Using Meteorological Data

Analytical solutions to estimate temperature with depth and stored energy within a soil column based upon readily available meteorological data are presented in this paper, which are of particular relevance in the field of ground heat extraction and storage. The transient one dimensional heat diffusion equation is solved with second kind (Neumann) boundary conditions at the base and third kind (Robin) boundary conditions, based on a heat balance, at the soil surface. In order to describe the soil-atmosphere interactions, mathematical expressions describing the daily and annual variation of solar radiation and air temperature are proposed. The presented analytical solutions are verified against a numerical solution and applied to investigate a case-study problem based upon results of a field experiment. It is shown that the proposed analytical approach can offer a reasonable estimate of the thermal behaviour of the soil requiring no information from the soil other than its thermal properties. Comparisons of predicted and measured soil temperature profiles and stored energy transients demonstrate there is reasonable overall agreement. The research contributes a practical approach that can provide surface boundary data that are vital in the thermal analysis of many engineering problems. Applications include: inter-seasonal heat transfer, energy piles and other more established ground source heat utilization methods.

Soil and biomass mercury emissions during a prescribed fire in the Amazonian rain forest

Mercury stored in forests can be volatilized to the atmosphere during fires. Many factors influence this process such as mercury concentration, vegetation loading and the soil temperature reached during the fire. We quantified mercury emissions from biomass and soil during a prescribed fire in Brazil using the difference in mercury burden in vegetation and soil before and after burning, and data were critically compared with those previously obtained in a similar experiment in another part of the Amazonia. The calculated mercury emission factor was 4.1 ± 1.4 g Hg ha−1, with the main part (78%) originating from litterfall and O-horizon, and only 14% associated with live biomass. When considering the fuel burned loading, the emission factor ranged from 40 to 53 μg Hg kg−1. Data were also obtained on soil temperature profile and on Hg speciation in soil in an effort to relate these parameters to Hg emissions.

Soil temperature profile and its readiness for controlling buildings indoors Temperature at Erbil city – Iraqi Kurdistan Region (IKR)

Soil temperature varies both diurnally and seasonally and can determine the temperature gradient within the collector loops of the ground source heat pump. To study spatial and temporal variations of soil temperature besides investigating the possibility of using underground soil temperature of the region for the installation of ground heat exchange systems, the current study was conducted. Soil temperature was measured at two locations in Erbil city/ IKR during the period from November, 1st, 2012 to February, 28th, 2013 with temperature sensors inserted in the ground at different depths. . It has been observed that during January and February the soil temperature offered the highest and lowest fluctuations respectively and they were closely related to ambient air temperature. The results also indicated that soil temperature increased with increasing depth up to a depth of 3.5 m in most cases and thereafter started to decrease with increasing depth. Furthermore, it was shown that the reliability of soil temperature prediction from air temperature decreased with the increase in soil depth. Positive differences at a depth of 3.5 m February ranged from 13.73 to 21.56o C during the winter season from December to. The results can be valuable in planning for preheating system during the cold seasons.

Supercritical Rankine Cycle Coupled with Ground Cooling for Low Temperature Power Generation

This paper presents an application of an earth-air-heat-exchanger (EAHE) as condenser in low to medium temperature power generation plants. A supercritical Rankine cycle (SRC) utilizing organic refrigerants as working fluids was used as the power cycle for the plant. The heat source temperature was varied from 125-1750C. The condenser was coupled to an EAHE system buried at a depth of 2 m under the surface of the earth. Its effect on the power cycle efficiency over a period of six months has been studied. It was observed that the soil temperature 10cm from the surface (horizontal direction) of the underground pipe increased by almost 20C during this time. This temperature change decreased with distance from the pipe. The soil temperature profile varied with time, distance from the pipe and location along the length of the pipe. The efficiency of the SRC increased by 1% and the daily fluctuations were reduced when EAHE was used.

Modeling impacts of film mulching on rainfed crop yield in Northern China with DNDC

Water stress is a major factor threatening agricultural production across a wide range of rainfed croplands in China. Drought threats would become worse along with climate change, especially in Northern China where the projected climate change scenarios indicated decreases in precipitation in the arid or semi-arid agricultural areas. Pilot experiments have been launched to search alternative farming management practices for adaptation of the climate change in China. Plastic film mulching (FM) has recently been tested at a number of sites in China with encouraging results although no any regional assessment has been done yet. This paper reports how we met the gap by testing a process-based, biogeochemical model, Denitrification-Decomposition or DNDC, against observations and then utilizing the model to upscale the simulations to a large region in China. DNDC was first modified by including a new module, which tracked variations of soil climate under the film mulching conditions. Two new input parameters, i.e., FM-covering fraction and duration, worked in conjunction with daily weather data to define the daily soil temperature and moisture profiles. By varying the FM coverage or duration, we could simulate a variety of FM settings and their impacts on the soil climate. A 3-year dataset of soil climate as well as crop yield measured at a rainfed corn field in Shaanxi Province in Northwestern China were used to serve the model validation tests. The measured and modeled results were in agreement with each other and both indicated that the FM practice substantially improved the soil moisture as well as the crop yield. Sensitivity tests were conducted with the revised DNDC by varying each of four factors, i.e., precipitation, temperature, soil texture and fertilizer application rate, in its range commonly observed in Northern China while keeping other input factors constant. Results from the sensitivity tests indicated that the effectiveness of FM was mainly related to precipitation. Efficiency of FM increased with decrease of precipitation. The FM effectiveness was evaluated at regional scale by linking DNDC to the databases holding spatially differentiated climate, soil and management data for all the 1.17 million ha of rainfed corn fields in the entire province of Shaanxi, across which the annual average precipitation decreased from 940mm in the south to 390mm in the north. Results from the regional simulation indicated that (1) corn production increased by 1.79 million tons or 16% with FM applications in the domain of Shaanxi; (2) the FM-induced increases in corn yield mainly occurred in the northern counties of the province where precipitation was lower than 700mm; and (3) the effectiveness of FM decreased with increase in precipitation from the northern to the southern areas in the domain. The study concluded that film mulching practice could play an important role in elevating rainfed crop yields in the arid or semi-arid regions in China.

Benchmarking of L-band soil microwave emission models

A first step before assimilating Soil Moisture and Ocean Salinity (SMOS) L-band brightness temperatures (Tb) over land is to couple land surface models (LSMs) to microwave emission models. In this study, the Interactions between Soil Biosphere and Atmosphere (ISBA) LSM is coupled to the Community Microwave Emission Modelling platform (CMEM). Simulations of Tb are performed over a 3-yr period (2003–2005) for a bare soil field in southwestern France, at the Surface Monitoring Of the Soil Reservoir EXperiment (SMOSREX) experimental site. Both ISBA and CMEM present several options for the representation of the soil moisture and soil temperature profiles. Simplified 2-layer simulations are compared with more detailed multilayer simulations. In the 2-layer simulations, the soil is divided into two layers (a thin surface layer and a bulk reservoir), and Fresnel laws are used in CMEM to model the smooth surface emissivity. In the multilayer simulations, the ISBA soil diffusion scheme is used (with 11 soil layers represented) together with either the Wilheit or Fresnel option of CMEM. The Tb simulations are compared to the Tb ground observations available for the SMOSREX site, at H and V polarizations and at different angles, and the impact of soil roughness is assessed. It is shown that taking surface soil moisture into account in the calculation of soil roughness improves the representation of the seasonal cycle and increases the correlation for all the versions of CMEM. The Tb derived from the most complex multilayer simulations correlate slightly better to the observations than the Tb derived from the 2-layer model (r=0.84 and r=0.82, respectively, for the pooled dataset). This is partly due to a better representation of the soil moisture profile. Finally, the multilayer model is used to investigate the L-band sampling depth for contrasting soil texture profiles. For a variety of soil textures, it is found that Tb are mainly driven by the top 15cm soil layer.

Short-term cropland responses to temperature extreme events during late winter

Abstract. In recent years, several studies have focused on terrestrial ecosystem response to extreme events. Most of this research has been conducted in natural ecosystems, but few have considered agroecosystems. In this study, we investigated the impact of a manipulated warmer or cooler late winter/early spring on the carbon budget and final harvest of a soybean crop (Glycine max (L.) Merr.). Soil temperature was altered by manipulating soil albedo by covering the soil surface with a layer of inert silica gravel. We tested three treatments – cooling (Co), warming (W), mix (M) – and control (C). An automated system continuously measured soil heterotrophic respiration (Rh), soil temperature profiles, and soil water content across the entire year in each plot. Phenological phases were periodically assessed and final harvest was measured in each plot. Results showed that treatments had only a transient effect on daily Rh rates, which did not result in a total annual carbon budget significantly different from control, even though cooling showed a significant reduction in final harvest. We also observed anticipation in emergence in both W and M treatments and a delay in emergence for Co. Moreover, plant density and growth increased in W and M and decreased in Co. In conclusion, from the results of our experiment we can assert that an increase in the frequency of both heat and cold waves is unlikely to have large effects on the overall annual carbon balance of irrigated croplands.

PEATBOG: a biogeochemical model for analyzing coupled carbon and nitrogen dynamics in northern peatlands

Abstract. Elevated nitrogen deposition and climate change alter the vegetation communities and carbon (C) and nitrogen (N) cycling in peatlands. To address this issue we developed a new process-oriented biogeochemical model (PEATBOG) for analyzing coupled carbon and nitrogen dynamics in northern peatlands. The model consists of four submodels, which simulate: (1) daily water table depth and depth profiles of soil moisture, temperature and oxygen levels; (2) competition among three plants functional types (PFTs), production and litter production of plants; (3) decomposition of peat; and (4) production, consumption, diffusion and export of dissolved C and N species in soil water. The model is novel in the integration of the C and N cycles, the explicit spatial resolution belowground, the consistent conceptualization of movement of water and solutes, the incorporation of stoichiometric controls on elemental fluxes and a consistent conceptualization of C and N reactivity in vegetation and soil organic matter. The model was evaluated for the Mer Bleue Bog, near Ottawa, Ontario, with regards to simulation of soil moisture and temperature and the most important processes in the C and N cycles. Model sensitivity was tested for nitrogen input, precipitation, and temperature, and the choices of the most uncertain parameters were justified. A simulation of nitrogen deposition over 40 yr demonstrates the advantages of the PEATBOG model in tracking biogeochemical effects and vegetation change in the ecosystem.

Reconciling soil thermal and hydrological lower boundary conditions in land surface models

The lower boundary condition of soil in land surface models is a key parameter, which can affect the energy and water budget at the surface/atmosphere interface. Indeed, it affects the thermal inertia of the ground as well as the water fluxes from the subsurface to the river‐aquifer system. In land surface models, it is well known that the soil must be sufficiently deep to compute a realistic soil temperature profile, while in terms of hydrology, the soil column should be substantially thinner in order to simulate realistic river discharges and therefore surface fluxes. In addition to the confirmation of this paradox, the goal of this study is to show how it is solved in the Interaction between Soil Biosphere Atmosphere (ISBA) land surface model. To reconcile hydrological and thermal lower boundary conditions, a simple approach is developed in which the soil temperature profile is extended below the hydrological column of the soil, and the water profile is extrapolated at each thermal node as the depth increases. ISBA is applied across France over 20 years and at a relatively high resolution. Additional experiments are also performed using the same lower boundary conditions of 1, 2, 3, 5, and 12 m for hydrological and thermal equations. The simulated river discharges and temperature profiles are compared to a dense network of in situ observations. The results confirm the paradox addressed previously and demonstrate that, if left unsolved, it could lead to poor simulation of the soil water and energy budgets, potentially affecting the performance of forecast studies, hydrological applications, and/or climate modeling.

Rainfall, Soil Water Content, and Groundwater Levels at the Riverlands Nature Reserve (South Africa)

Quantified medium- and long-term hydrological datasets are scarce in South Africa, yet they are essential to gain understanding of natural systems, contribute to ecosystem conservation, and ultimately quantify water balance processes accurately. A hydrological experiment was carried out at Riverlands Nature Reserve (Western Cape, South Africa) in order to quantify the components of the soil water balance at experimental sites occupied by endemic and invasive vegetation. In two separate follow-up projects, five-year time series were collected in three treatments, namely, endemic fynbos vegetation, bare soil, and land invaded by Acacia saligna. Rainfall was recorded daily with a manual rain gauge. Groundwater levels were logged hourly at 14 boreholes. Volumetric soil water contents and soil temperatures were logged hourly at different depths in the soil profile. Groundwater levels and soil water contents responded to rainfall with very clear seasonal trends. The data can be applied in water balance and evapotranspiration studies, unsaturated flux studies, soil temperature profile studies, and rainfall-groundwater level response analysis and for calibrating and validating a wide range of hydrological models.