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  • 1
    Language: English
    In: Journal of Hydrology, Feb 25, 2013, Vol.481, p.106(13)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.jhydrol.2012.12.024 Byline: Gonzalo Martinez (a)(b), Yakov A. Pachepsky (b), Harry Vereecken (c), Horst Hardelauf (c), Michael Herbst (c), Karl Vanderlinden (d) Keywords: Soil water content; Temporal stability; Simulations; Local controls; Saturated hydraulic conductivity Abstract: a* We simulated soil water flow in bare and grassed soil columns of three textures. a* Typical features of soil water temporal stability were recovered in simulations. a* Simulated duration and season affected the temporal stability of soil water contents. a* Spatio-temporal variations in soil water correlated with soil hydraulic conductivity. Author Affiliation: (a) Dept. of Agronomy, University of Cordoba, 14071 Cordoba, Spain (b) USDA-ARS- Environmental Microbial and Food Safety Lab, Beltsville, MD 20705, USA (c) Agrosphere (IBG-3), Institute of Bio- and Geosciences, Forschungszentrum Julich GmbH, 52428 Julich, Germany (d) IFAPA, Centro Las Torres-Tomejil, 41200 Alcala del Rio, Spain Article History: Received 15 December 2011; Revised 14 December 2012; Accepted 17 December 2012 Article Note: (miscellaneous) This manuscript was handled by Corrado Corradini, Editor-in-Chief, with the assistance of Axel Bronstert, Associate Editor
    Keywords: Hydrogeology -- Models ; Food Safety -- Models ; Soil Moisture -- Models ; Hydraulic Flow -- Models ; Water -- Models
    ISSN: 0022-1694
    Source: Cengage Learning, Inc.
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  • 2
    Language: English
    In: Journal of Hydrology, 25 February 2013, Vol.481, pp.106-118
    Description: ► We simulated soil water flow in bare and grassed soil columns of three textures. ► Typical features of soil water temporal stability were recovered in simulations. ► Simulated duration and season affected the temporal stability of soil water contents. ► Spatio-temporal variations in soil water correlated with soil hydraulic conductivity. Occurrence of temporal stability of soil water content has been observed for a range of soil and landscape conditions and is generally explained as a consequence of local and non-local controls. However, the underlying factors for this phenomenon are not completely understood and have not been quantified. This work attempts to elucidate and quantify the effects of several local controls, such as soil hydraulic properties and root water uptake, through water flow simulations. One-dimensional water flow was simulated with the HYDRUS code for bare and grassed sandy loam, loam and clay soils at different levels of variability in the saturated hydraulic conductivity . Soil water content at 0.05 and 0.60 m and the average water content of the top 1 m were analyzed. Temporal stability was characterized by calculating the mean relative differences of soil water content in 100 soil columns used for each combination of soil and season. Using log-normal distributions of resulted in mean relative differences distributions that were commonly observed in experimental studies of soil water content variability. Linear relationships were observed between scaling factor of ln and spread of the mean relative differences distributions. For the same scaling factor and soil texture, simulated shapes of the mean relative differences distributions depended on the duration of the simulation period and the season. Variation in mean relative differences was higher in coarser textures than in finer ones and more variability was seen in the topsoil than in the subsoil. Root water uptake decreased the mean relative differences variability in the root zone and increased variability below it. This work presents a preliminary research to promote the use of water flow simulations under site-specific conditions to better understand the temporal stability of soil water contents. The estimation of the spatial variability of from soil water content monitoring presents an interesting avenue for further research.
    Keywords: Soil Water Content ; Temporal Stability ; Simulations ; Local Controls ; Saturated Hydraulic Conductivity ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 3
    Language: English
    In: Vadose Zone Journal, 2012, Vol.11(4), pp.1-19
    Description: Temporal stability (TS) of soil water content (SWC) has been observed throughout a wide range of spatial and temporal scales. Yet, the evidence with respect to the controlling factors on TS SWC remains contradictory or nonexistent. The objective of this work was to develop the first comprehensive review of methodologies to evaluate TS SWC and to present and analyze an inventory of published data. Statistical analysis of mean relative difference (MRD) data and associated standard deviations (SDRD) from 157 graphs in 37 publications showed a trend for the standard deviation of MRD (SDMRD) to increase with scale, as expected. The MRD followed generally the Gaussian distribution with R2 ranging from 0.841 to 0.998. No relationship between SDMRD and R2 was observed. The smallest R2 values were mostly found for negatively skewed and platykurtic MRD distributions. A new statistical model for temporally stable SWC fields was proposed. The analysis of the published data on seven measurement-, terrain-, and climate-related potentially controlling factors of TS SWC suggested intertwined effects of controlling factors rather than single dominant factors. This calls for a focused research effort on the interactions and effects of measurement design, topography, soil, vegetation and climate on TS SWC. Research avenues are proposed which will lead to a better understanding of the TS phenomenon and ultimately to the identification of the underlying mechanisms. ; p. 1-19.
    Keywords: Soil Water Content ; Topography ; Statistical Analysis ; Statistical Models ; Vegetation ; Climate ; Temporal Variation
    ISSN: 1539-1663
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  • 4
    In: Water Resources Research, June 2014, Vol.50(6), pp.4837-4857
    Description: We examined 3 years of measured daily values of all major water budget components (precipitation , potential evapotranspiration , actual evapotranspiration , and runoff ) and volumetric soil water content of a small, forested catchment located in the west of Germany. The spatial distribution of was determined from a wireless sensor network of 109 points with 3 measurement depths each; was calculated from eddy‐covariance tower measurements. The water budget was dominantly energy limited, with amounting to approximately 90% of , and a runoff ratio of 56%. , , and closed the long‐term water budget with a residual of 2% of precipitation. On the daily time scale, the residual of the water budget was larger than on the annual time scale, and explained to a moderate extent by ( = 0.40). Wavelet analysis revealed subweekly time scales, presumably dominated by unaccounted fast‐turnover storage terms such as interception, as a major source of uncertainty in water balance closure. At weekly resolution, soil water content explained more than half ( = 0.62) of the residual. By means of combined empirical orthogonal function and cluster analysis, two slightly different spatial patterns of could be identified that were associated with mean values below and above 0.35 cm/cm, respectively. The timing of these patterns as well as the varying coherence between , , and soil water content responded to changes in water availability, including a moderate response to the European drought in spring 2011. Water budget and distributed soil water content of small catchment analyzed Budget closed on annual basis, short‐term residual correlated with water content EOF analysis reveals two patterns, hysteresis relation to mean water content
    Keywords: Soil Water Content ; Evapotranspiration ; Precipitation ; Runoff ; Balance
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 5
    In: Water Resources Research, June 2005, Vol.41(6), pp.n/a-n/a
    Description: With time‐lapse electrical resistivity tomography (ERT), transport processes in the subsurface can be imaged and monitored. The information content of obtained spatiotemporal data sets opens new ways to characterize subsurface spatial variability. Difficulties regarding a quantitative interpretation of the imaged transport may arise from the fact that data inversion used in ERT is generally underdetermined and that ERT data acquisition is often limited to two‐dimensional (2‐D) image planes. To address this problem, we conducted a numerical tracer experiment in a synthetic heterogeneous aquifer with preset variability and spatial correlation of the hydraulic conductivity and monitored the tracer breakthrough in a 2‐D image plane perpendicular to the mean flow direction using time‐lapse ERT. The tracer breakthrough patterns in the image plane were interpreted using equivalent transport models: an equivalent convection dispersion equation to characterize the spatially averaged breakthrough and a stream tube model to characterize local breakthrough curves. Equivalent parameters derived from simulated and from ERT inverted concentrations showed a good agreement, which demonstrates the potential of ERT to characterize subsurface transport. Using first‐order approximate solutions of stochastic flow and transport equations, equivalent model parameters and their spatial variability were interpreted in terms of the local‐scale dispersion and the spatial variability of the hydraulic conductivity. The spatial correlations of the stream tube velocity and of the hydraulic conductivity were found to be closely related. Consequently, the hydraulic conductivity spatial correlation may be inferred from stream tube velocity distributions, which can be observed with sufficiently high spatial resolution using ERT.
    Keywords: Electrical Resistivity Tomography ; Equivalent Transport Models ; Stream Tube Model ; Tracer Tests
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 6
    Language: English
    In: Computers and Geosciences, 2008, Vol.34(12), pp.1958-1963
    Description: In this paper, we present a class of preconditioning methods for a parallel solution of the three-dimensional Richards equation. The preconditioning methods Jacobi scaling, block-Jacobi, incomplete lower–upper, incomplete Cholesky and algebraic multigrid were applied in combination with a parallel conjugate gradient solver and tested for robustness and convergence using two model scenarios. The first scenario was an infiltration into initially dry, sandy soil discretised in 500,000 nodes. The second scenario comprised spatially distributed soil properties using 275,706 numerical nodes and atmospheric boundary conditions. Computational results showed a high efficiency of the nonlinear parallel solution procedure for both scenarios using up to 64 processors. Using 32 processors for the first scenario reduced the wall clock time to slightly more than 1% of the single processor run. For scenario 2 the use of 64 processors reduces the wall clock time to slightly more than 20% of the 8 processors wall clock time. The difference in the efficiency of the various preconditioning methods is moderate but not negligible. The use of the multigrid preconditioning algorithm is recommended, since on average it performed best for both scenarios.
    Keywords: Three-Dimensional ; Multi-Processor ; Unsaturated Flow ; Water Flow ; Preconditioner ; Multigrid ; Geology
    ISSN: 0098-3004
    E-ISSN: 1873-7803
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