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  • 1
    ISSN: 0992-7689
    Keywords: Hydrology (evapotranspiration; soil moisture; water-energy interactions)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract The MUREX (monitoring the usable soil reservoir experimentally) experiment was designed to provide continuous time series of field data over a long period, in order to improve and validate the Soil-vegetation-Atmosphere Transfer (SVAT) parameterisations employed in meteorological models. Intensive measurements were performed for more than three years over fallow farmland in southwestern France. To capture the main processes controlling land-atmosphere exchanges, the local climate was fully characterised, and surface water and energy fluxes, vegetation biomass, soil moisture profiles, surface soil moisture and surface and soil temperature were monitored. Additional physiological measurements were carried out during selected periods to describe the biological control of the fluxes. The MUREX data of 1995, 1996, and 1997 are presented. Four SVAT models are applied to the annual cycle of 1995. In general, they succeed in simulating the main features of the fallow functioning, although some shortcomings are revealed.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Computing 32 (1984), S. 343-355 
    ISSN: 1436-5057
    Keywords: 41A28 ; 65D25 ; Čebyšev-nodes ; numerical differentiation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Computer Science
    Description / Table of Contents: Abstract Letp n denote the polynomial of degreen or less that interpolates a given smooth functionf at the Čebyšev nodest j n =cos(jπ/n), 0≤j≤n, and let ‖·‖ be the maximum norm inC[−1, 1]. It is proved that fork-th derivatives (2≤k≤n) estimates of the following type hold $$\parallel f^{(k)} - p_n^{(k)} \parallel \leqslant c_k n^{k - 1} \inf \{ \parallel f^{(k)} - q\parallel :q \in \Pi _{n - k} \} .$$ In this relationc k only depends onk andΠ n−k denotes the space of polynomials up to degreen−k.
    Notes: Zusammenfassung Seip n das Polynom vom Maximalgradn, das eine gegebene Funktionf an den Čebyšev-Knotent j n =cos (jπ/n), 0≤j≤n, interpoliert, und ‖·‖ die Maximumnorm imC[−1,+1]. Es wird gezeigt, daß fürk-te Ableitungen (2≤k≤n) Abschätzungen folgender Art gelten: $$\parallel f^{(k)} - p_n^{(k)} \parallel \leqslant c_k n^{k - 1} \inf \{ \parallel f^{(k)} - q\parallel :q \in \Pi _{n - k} \} .$$ Hier hägtc k nur vonk ab undΠ n−k ist der Raum der Polynome vom Maximalgradn−k.
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  • 3
    ISSN: 1573-1472
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract A simplified land-surface parameterization is tested against bare-soil data collected during the EFEDA experiment conducted in Spain in June 1991. A complete data set, made up of soil properties as well as hydrological and atmospheric measurements, is described and discussed. The 11-day data set is characterized by very dry conditions and high surface temperatures during the day. Large values of sensible and soil heat fluxes and small values of surface evaporation (≈1 mm/day) were observed. This data set was modelled, leading to the following conclusions: (i) In the model, the parameterization provides values of the soil thermal properties and subsequently of the predicted soil heat fluxes which are overestimated when compared with the observations. (ii) Following the literature, a value of the ratio between the roughness lengths for momentumZ oand heatZ ohof close to 10 for fairly homogeneous areas of bare soil and vegetation is used. This value leads to a fair prediction of the surface temperature. If the roughness lengths were taken to be equal, as is often assumed in atmospheric modelling, a poorer prediction results. (iii) Finally, the vapor phase transfer mode is found dominant close to the surface and a modified parameterization including this effect is proposed. It allows a fair prediction of both surface evaporation and near-surface water content.
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  • 4
    ISSN: 1573-1634
    Keywords: Infiltration ; layered soils ; impervious surface
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The interaction of a wetting front with an impervious surface can be described very easily in the early stages of interaction by using a superposition principle. After the time when the superposition principle fails to describe the interaction properly, two flow regimes are analysed. For most of the interaction the profile is only affected by the impervious surface near that surface and in particular the inflow into the soil layer is unchanged. Then, only at the very end of the process is the inflow decreasing because of the impervious surface.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1573-1634
    Keywords: Water-retention curve ; capillary-rise fitting parameters
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The constraints on the different fitting parameters used in the water-retention equations of Brooks and Corey, Brutsaert, and Van Genuchten are analyzed. It is shown that in the dry part of the h(θ) curve all three equations might break down for clay soils when the fitting parameters are calculated by a best fit over observed field data. In that case, application of the h(θ) equations for water transfer dealing with the very dry parts of the water retention curve can lead to erroneous results and must be limited to the range of water contents of the original data set.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Springer
    Transport in porous media 24 (1996), S. 315-339 
    ISSN: 1573-1634
    Keywords: water movement ; infiltration ; water balance ; analytical solutions ; hydraulic properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract Simple equations for predicting infiltration of water into soil are valuable both for hydrological application and for investigating soil hydraulic properties. Their value is greatly enhanced if they involve parameters that can be related to more basic soil hydraulic properties. In this paper we extend infiltration equations developed previously for positive surface heads to negative heads. The equations are then used to calculate infiltration into a sand and a clay for a range of initial and surface conditions. Results show errors of less than three percent compared with accurate numerical solutions. Analytical approximations to parameters in the equations are developed for a Brooks and Corey power law hydraulic conductivity-water content relation combined with either a Brooks and Corey or a van Genuchten water retention function. These are compared with accurate numerical values for a range of hydraulic parameters encompassing the majority of soil types and a range of initial and boundary conditions. The approximations are excellent for a wide range of soil parameters. An important attribute of the infiltration equations is their use of dimensionless parameters that can be calculated from normalised water retention and hydraulic conductivity functions. These normalised functions involve only parameters that it may be possible to estimate from surrogate data such as soil particle size distribution. Application of the equations for predicting infiltration, or their use in inferring hydraulic properties, then involves only simple scaling parameters.
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Transport in porous media 15 (1994), S. 197-208 
    ISSN: 1573-1634
    Keywords: Heaslet-Alksne technique ; Bruce and Klute equation ; unsaturated flow ; moments ; sorptivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract An estimate of the sorptivity that requires only the knowledge of simple integrals of the soil-water diffusivity weighted by a power of the water content is present. The result is checked systematically for diffusivity functions with very different behaviours: power law, exponential and the two Fujita diffusivities. In all cases the error is always less than 1% regardless of whether or not the diffusivity increases rapidly with water content.
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  • 8
    ISSN: 1573-1634
    Keywords: Infiltration ; layered soils ; superposition of solutions ; impervious surface
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract The interaction of a wetting front with an impervious layer is described by adding a reflected solution to the incoming solution for a semi-infinite medium. It is shown and checked by comparison with a numerical solution that the result is accurate during the early times of the interaction between the front and the impervious surface. This superposition principle is quite general and should prove especially useful to initiate numerical schemes by this analytical approximation as in the early times singularities are difficult to describe numerically.
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  • 9
    ISSN: 1573-1634
    Keywords: nonlinear diffusion ; analytic solutions ; exact solutions ; approximations ; similarity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Notes: Abstract A general approximation for the solution of the one-dimensional nonlinear diffusion equation is presented. It applies to arbitrary soil properties and boundary conditions. The approximation becomes more accurate when the soil-water diffusivity approaches a delta function, yet the result is still very accurate for constant diffusivity suggesting that the present formulation is a reliable one. Three examples are given where the method is applied, for a constant water content at the surface, when a saturated zone exists and for a time-dependent surface flux.
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  • 10
    ISSN: 1573-1634
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Technology
    Type of Medium: Electronic Resource
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