Submitted to: Encyclopedia of Soil Science
Publication Type: Book / Chapter
Publication Acceptance Date: July 1, 2001
Publication Date: April 10, 2002
Interpretive Summary: A pervasive problem in soil hydrology, and in soil science in general, is the need in representation of processes at a scale different from the one at which observations and property measurements are made. This scale-transfer problem must be solved, in particular, to describe effectively the coupled fluxes of heat and moisture across land surfaces, to establish appropriate soil parameters for describing the long-term fate of pollutants, to interpret remote sensing data, to delineate management zones in agricultural fields, to estimate water yield and geochemical fluxes in ungauged watersheds, and to provide parameters for estimating biogeochemical trends related to the climate change. This special entry of the Encyclopedia of Soil Science has been planned to address the issue of multiscale characterization of soil hydrological parameters. This entry identifies hierarchical soil heterogeneity as a cause of scale-dependence in soil parameters and describes both physics-based and empirical scaling procedures developed to-date. Examples are given to illustrate applicability of those procedures to data on plot, field and regional measurement scales. Reference sources are included. A reader is expected to become aware of the scale effects in soil hydrology, and to become familiar with ideas behind scaling methods.
Soil moisture and soil hydraulic properties of soils are measured over temporal and spatial measurement scales that are different to the scale at which knowledge is required. A special entry of the Encyclopedia of Soil Science has been planned to address the issue of multiscale characterization of soil hydrological parameters. The reason for scale effects is that the larger scale represents levels of heterogeneity in soi structure that are absent in small-scale volumes. Physics-based scaling uses models of soil structure that assume preservation of some structure-related properties across a range of measurement scales or among samples of the same measurement scale. Similitude-based scaling, scaling invariance of water transport equations, fractal scaling from self-similarity, self-affinity, and multiscaling hypotheses are described. Changing water transport models with scale is introduced. Empirical scaling gis viewed as a mean to transition from one physics-based scaling regime to another. Soil structure and soil landscape relationships provide the information for such type of scaling. Inverse modeling as a tool to obtain scale-dependent hydraulic properties is described. Reference sources and examples of application are given. A reader is expected to become aware of the scale effects in soil hydrology, and to become familiar with ideas behind current scaling methods.