A re-examination of modeled and measured soil moisture spatial variability and its implications for land surface modeling

Abstract Using a spatially distributed water and energy balance model, we investigate the spatial structure of surface fluxes and states for the Washita '92 field experiment and the August campaign of the Washita '94 field experiments. For Washita '92, the model is validated against gravimetric and remotely sensed soil moisture, and for Washita '94, the model is validated against gravimetric soil moisture and measured energy fluxes. The model is shown to reasonably represent land–atmosphere interactions during the experimental periods. Scaling analysis of remotely sensed and modeled soil moisture and modeled latent heat flux is indicative of multiscaling behavior. The temporal behavior of the soil moisture scaling exponents for various moments suggests the existence of three distinct regimes during a dry-down. The multiscaling behavior inferred from simulated soil moisture and latent heat flux is hypothesized as a relationship which is a function of average soil moisture. Similar scaling analysis of important land surface properties indicates simple scaling for porosity, field capacity and wilting point, and multiscaling for residual soil moisture, leaf area index and the soils-topographic index. This is consistent with model results, which indicate a transition from simple scaling to multiscaling with dry-down. It is hypothesized that this transition is governed by the scaling properties which in wet conditions control infiltration (porosity, field capacity, leaf area index) to properties which in dry conditions control drainage (residual moisture content and soils-topographic index) and evaporation (wilting point, leaf area index). Land surface models which fail to incorporate these features will most likely be unable to capture the dynamic nature of soil moisture spatial variability.

[1]  Andrea Rinaldo,et al.  Self‐organized river basin landscapes: Fractal and multifractal characteristics , 1994 .

[2]  Eric F. Wood,et al.  Scale Dependence and Scale Invariance in Hydrology: Scale Analyses for Land-Surface Hydrology , 1998 .

[3]  Eric F. Wood,et al.  Effects of soil moisture aggregation on surface evaporative fluxes , 1997 .

[4]  Scaling, soil moisture and evapotranspiration in runoff models , 1994 .

[5]  V. Gupta,et al.  Multiscaling properties of spatial rain-fall and river flow distributions , 1990 .

[6]  Eric F. Wood,et al.  The Effect of Soil Thermal Conductivity Parameterization on Surface Energy Fluxes and Temperatures , 1998 .

[7]  P. A. Burrough,et al.  Multiscale sources of spatial variation in soil. I: The application of fractal concepts to nested levels of soil variation , 1983 .

[8]  S. Islam,et al.  Multiscaling properties of soil moisture images and decomposition of large- and small-scale features using wavelet transforms , 1998 .

[9]  A. Rinaldo,et al.  On the spatial organization of soil moisture fields , 1995 .

[10]  Wilfried Brutsaert,et al.  Evaporation into the atmosphere : theory, history, and applications , 1982 .

[11]  Eli Skop,et al.  Scale Issues in Hydrological Modeling , 1996 .

[12]  Eric F. Wood,et al.  Scaling behaviour of hydrological fluxes and variables: Empirical studies using a hydrological model and remote sensing data , 1995 .

[13]  D. L. Brakensiek,et al.  Estimation of Soil Water Properties , 1982 .

[14]  K. Beven,et al.  A physically based, variable contributing area model of basin hydrology , 1979 .

[15]  Günter Blöschl,et al.  Preferred states in spatial soil moisture patterns: Local and nonlocal controls , 1997 .

[16]  Garrison Sposito,et al.  Scale Dependence and Scale Invariance in Hydrology , 1998 .

[17]  R. Pielke.  Mesoscale Meteorological Modeling , 1984 .

[18]  Eric F. Wood,et al.  Effects of Spatial Variability and Scale on Areally Averaged Evapotranspiration , 1995 .

[19]  K. Beven,et al.  Similarity and scale in catchment storm response , 1990 .

[20]  T. Jackson,et al.  Investigation of the accuracy of soil moisture inversion using microwave data and its impact on watershed hydrological modeling , 1996, IGARSS '96. 1996 International Geoscience and Remote Sensing Symposium.

[21]  Eric F. Wood,et al.  A soil‐vegetation‐atmosphere transfer scheme for modeling spatially variable water and energy balance processes , 1997 .

[22]  Günter Blöschl,et al.  Observed spatial organization of soil moisture and its relation to terrain indices , 1999 .

[23]  Keith Beven,et al.  On hydrologic similarity: 2. A scaled model of storm runoff production , 1987 .

[24]  J. Famiglietti,et al.  Multiscale modeling of spatially variable water and energy balance processes , 1994 .

[25]  J. Noilhan,et al.  Sensitivity study and validation of a land surface parameterization using the HAPEX-MOBILHY data set , 1990 .

[26]  William P. Kustas,et al.  Variability in surface energy flux partitioning during Washita '92 : Resulting effects on Penman-Monteith and Priestley-Taylor parameters , 1996 .

[27]  Eric F. Wood,et al.  Application of multiscale water and energy balance models on a tallgrass prairie , 1994 .

[28]  Bin Li,et al.  The impact of spatial variability of land-surface characteristics on land-surface heat fluxes , 1994 .

[29]  T. Jackson,et al.  Mapping surface soil moisture using an aircraft-based passive microwave instrument: algorithm and example , 1996 .