Soil moisture modeling with ERA5-Land retrievals, topographic indices, and in situ measurements and its use for predicting ruts
Marian SchönauerAnneli ÅgrenKlaus KatzensteinerFlorian HartschPaul A. ArpSimon DrollingerDirk Jaeger
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Abstract. Spatiotemporal modeling is an innovative way of predicting soil moisture and has promising applications that support sustainable forest operations. One such application is the prediction of rutting, since rutting can cause severe damage to forest soils and ecological functions. In this work, we used ERA5-Land soil moisture retrievals and several topographic indices to model variations in the in situ soil water content by means of a random forest model. We then correlated the predicted soil moisture with rut depth from different trials. Our spatiotemporal modeling approach successfully predicted soil moisture with Kendall's rank correlation coefficient of 0.62 (R2 of 64 %). The final model included the spatial depth-to-water index, topographic wetness index, stream power index, as well as temporal components such as month and season, and ERA5-Land soil moisture retrievals. These retrievals were shown to be the most important predictor in the model, indicating a large temporal variation. The prediction of rut depth was also successful, resulting in Kendall's correlation coefficient of 0.61. Our results demonstrate that by using data from several sources, we can accurately predict soil moisture and use this information to predict rut depth. This has practical applications in reducing the impact of heavy machinery on forest soils and avoiding wet areas during forest operations.Neutron instrument is a high-tech,intelligent and advanced instrument,it is extensively used in measuring soil moisture content without disturbing soil in fieldwork,can be easily operated to successively monitor soil moisture content at any depths at the same measuring site,the measurement does not be limited by seasons,change of physical and chemical properties of soils,and can be connected with automatically recording system and computer.Neutron instrument is extensively used in many domains,such as pedology,geography,agriculture,forestry,meteorology,hydrogeology,and water conservancy and building projects.In this paper,the calibrating equation of soil moisture content measured with neutron instrument is developed,and the methods for increasing the measuring precision of shallow soil moisture content are researched,compared and verified. The traditional dying method is regarded as the criterion in measuring soil moisture content.The test results are calibrated and verified in field.The result shows that the hierarchical-section method is optimal in calibrating shallow soil moisture,and the relative errors are lower than 10%,which can satisfy the requirements of measuring shallow soil moisture content;the measuring precision of shallow soil moisture content can not be increased by the indirect derivation using deep soil moisture content;the results of shallow soil moisture content calibrated with the regressed equation of nonlinear least square method are not stable,and the test errors are high.Generally,it is considered that the detecting radius of neutron instrument is related to soil properties and moisture content.
Neutron probe
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An instrument for making rapid measurements of the soil moisture content in the root zone is an essential tool for many applications, including understanding of soil water dynamics, evaluation of agriculture water stress, and validation of soil moisture modeling. Studies have shown that electrical resistance measurements may be used to infer soil moisture content under special circumstances. In this paper, electrical resistivity (resistance multiplied by a geometric factor) measurements of the soil by the Geometrics Inc. OhmMapper instrument are compared with point measurements of soil moisture to a depth of 70 cm. It was found that the OhmMapper resistivity measurements could be used to infer soil moisture content with a coefficient of determination as high as 0.34 when a simple power law relationship was used. A more sophisticated analysis of the resistivity measurements could potentially lead to a greater coefficient of determination.
Pedotransfer function
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Summary Moisture content and bulk density largely characterize physical and mechanical soil status and behaviour. A nondestructive determination of these soil properties is essential. Time domain reflectometry (TDR), although widely accepted for determination of volumetric water content, θ , has its limitations, and recently a frequency domain (FD) sensor has been developed and tested. An equation relating relative permittivity, ɛ′, to gravimetric water content, w , and bulk density, p , was established for three soil types (sand, sandy loam and clay). If ɛ′ and w are known, our model can be used to calculate bulk density and associated volumetric water content, θ , keeping in mind that θ= pw. Utilization is found in long‐term monitoring of moisture fluctuations or short‐term detection of traffic‐induced soil compaction.
Gravimetric analysis
Reflectometry
Water retention curve
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Abstract A soil moisture content map is important for providing information about the distribution of moisture in a given area. Moisture content directly influences agricultural yield thus it is crucial to have accurate and reliable information about moisture distribution and content in the field. Since soil is a porous medium modified generalized Archie’s equation provides the basic formula to calculate moisture content data based on measured EC a . In this study we aimed to find a more accurate and cost effective method for measuring moisture content than manual field sampling. Locations of 25 sampling points were chosen from our research field as a reference. We assumed that soil moisture content could be calculated by measuring apparent electrical conductivity (EC a ) using the Veris-3100 on-the-go soil mapping tool. Statistical analysis was carried out on the 10.791 EC a raw data in order to filter the outliers. The applied statistical method was ±1.5 interquartile (IRQ) distance approach. The visualization of soil moisture distribution within the experimental field was carried out by means of ArcGIS/ArcMAP using the inverse distance weighting interpolation method. In the investigated 25 sampling points, coefficient of determination between calculated volumetric moisture content data and measured EC a was R 2 = 0.87. According to our results, volumetric moisture content can be mapped by applying EC a measurements in these particular soil types.
Inverse distance weighting
Pedotransfer function
Interpolation
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Summary Time‐domain reflectometry (TDR) is being used increasingly for measuring the moisture content of porous media. However, successful application for measuring water in soil has been limited to non‐deformable soils, and it would be a valuable extension of the technique if it could be used for soils that shrink on drying. We have recently investigated its application to soils rich in clay and organic matter and peats. Here we propose a method for determining moisture content in deformable soils based on the relation between the dielectric constant, K , and the volumetric moisture content, Θ, measured by TDR. Parallel TDR probes with a length of 15 cm and a spacing of 2 cm were placed horizontally in soil cores with a diameter of 20 cm and height of 10 cm taken from a forest. The soil is very porous with large proportions of both silt and clay. The sample weight and travel time of the electromagnetic wave guided by parallel TDR probes were simultaneously measured as a function of time, from saturation to oven‐dryness during which the core samples shrank considerably. Vertical and horizontal components of shrinkage were also measured to take the air‐exposed region of TDR probe into account in the determination of K . The effect of deformation on volumetric moisture content was formulated for two different expressions, namely actual volumetric moisture content (AVMC) and fictitious (uncorrected) volumetric moisture content (FVMC). The effects of air‐exposure and expressions of volumetric moisture content on the relation between K and Θ were examined by fitting the observations with a third‐order polynomial. Neglecting the travel time in the air‐exposed part or use of the FVMC underestimated the Θ for a given K . The difference was more pronounced between AVMC and FVMC than between two different dielectric constants, i.e. accounting for air‐exposure, K ac , and not accounting for air‐exposure, K au . When the existing empirical models were compared with the fitted results, most underestimated the relation based on the AVMC. This indicates that published empirical models do not reflect the effect of deformation on the determination of Θ in our forest soil. Correct use of the Θ expression has more impact on determining moisture content of a deformable soil than the accommodation of travel time through the air‐exposed region of TDR probe.
Reflectometry
Silt
Shrinkage
Saturation (graph theory)
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Pedotransfer function
Permanent wilting point
Biometeorology
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Pedotransfer function
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Hygrometer
Pedotransfer function
Soil moisture sensor
Alkalinity
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summary Hillslopes are fundamental landscape units, yet represent a difficult scale for measurements as they are well-beyond our traditional point-scale techniques. Here we present an assessment of electromagnetic induction (EM) as a potential rapid and non-invasive method to map soil moisture patterns at the hillslope scale. We test the new multi-frequency GEM-300 for spatially distributed soil moisture measurements at the well-instrumented Panola hillslope. EM-based apparent conductivity measurements were linearly related to soil moisture measured with the Aqua-pro capacitance sensor below a threshold conductivity and represented the temporal patterns in soil moisture well. During spring rainfall events that wetted only the surface soil layers the apparent conductivity measurements explained the soil moisture dynamics at depth better than the surface soil moisture dynamics. All four EM frequencies (7.290, 9.090, 11.250, and 14.010 kHz) were highly correlated and linearly related to each other and could be used to predict soil moisture. This limited our ability to use the four different EM frequencies to obtain a soil moisture profile with depth. The apparent conductivity patterns represented the observed spatial soil moisture patterns well when the individually fitted relationships between measured soil moisture and apparent conductivity were used for each measurement point. However, when the same (master) relationship was used for all measurement locations, the soil moisture patterns were smoothed and did not resemble the observed soil moisture patterns very well. In addition the range in calculated soil moisture values was reduced compared to observed soil moisture. Part of the smoothing was likely due to the much larger measurement area of the GEM-300 compared to the soil moisture measurements.
Pedotransfer function
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Understanding soil moisture variability and its relationship with water content at various scales is a key issue in hydrological research. In this paper we predict this relationship by stochastic analysis of the unsaturated Brooks‐Corey flow in heterogeneous soils. Using sensitivity analysis, we show that parameters of the moisture retention characteristic and their spatial variability determine to a large extent the shape of the soil moisture variance‐mean water content function. We demonstrate that soil hydraulic properties and their variability can be inversely estimated from spatially distributed measurements of soil moisture content. Predicting this relationship for eleven textural classes we found that the standard deviation of soil moisture peaked between 0.17 and 0.23 for most textural classes. It was found that the β parameter, which describes the pore‐size distribution of soils, controls the maximum value of the soil moisture standard deviation.
Pedotransfer function
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