USE OF LIMITED SOIL PROPERTY DATA AND MODELING TO ESTIMATE ROOT ZONE SOIL WATER CONTENT.

Authors: Starks, Patrick; Heathman, Gary; Ahuja, Lajpat; Ma, Liwang

Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2002
Publication Date: 2/10/2003
Citation: STARKS, P.J., HEATHMAN, G.C., AHUJA, L.R., MA, L. USE OF LIMITED SOIL PROPERTY DATA AND MODELING TO ESTIMATE ROOT ZONE SOIL WATER CONTENT.. JOURNAL OF HYDROLOGY. 2003. v. 272 p. 131-147.

Interpretive Summary: Modeling root zone soil water content at watershed scales is important for the management of water resources, but detailed soil property data required by many soil water models is often too expensive or impractical to obtain over large land areas. The objective of this study was to model root zone soil water content using a hierarchy of soil input data, ranging from soil texture class only, to measured soil texture and bulk densities of soil horizons, to additional laboratory or field measurements of soil water matric potentials and field measurements of average soil hydraulic properties. A state-of-the-art soil water model was used to estimate soil water content in the 0-60 cm soil layer for five soil data input scenarios at five sites within the Little Washita River Experimental Watershed, located in south central Oklahoma. The water content estimates from the five scenarios were compared to measured values, with the smallest root mean square errors, ranging from 1.2 to 1.8% volumetric water content, achieved using either the soil textural class only or the field-measured hydraulic properties. The results indicate that root zone soil water content can be adequately modeled using soil texture class alone. Near-surface soil texture information derived from remotely sensed surface soil moisture data could be combined with soil water models to derive the spatial distribution of root zone soil water content at the watershed scale, thereby allowing development of new or improved water resource management tools.

Technical Abstract: Modeling root zone soil water content at watershed scales is important for both the strategic and tactical management of water resources, but detailed soil physical and hydraulic property data required by most physically-based soil water models are generally not available over large land areas. With a view towards remote sensing applications in watershed hydrology, the objective of this study was to model root zone soil water content using a hierarchy of soil input data, ranging from soil texture name only, to measured soil texture and bulk densities of soil horizons, to additional laboratory or field measurements of soil water matric potentials and field measurements of average soil hydraulic properties. The Root Zone Water Quality Model was used to estimate soil water content in the 0-60 cm soil layer for five data input scenarios at five sites within the Little Washita River Experimental Watershed, located in south central Oklahoma. The water content estimates from the five scenarios were compared to measured values, with the smallest root mean square errors, ranging from 1.2 to 1.8% volumetric water content, achieved using either the soil textural class only or the field-measured hydraulic properties. The results indicate that root zone soil water content can be adequately modeled using soil texture name alone. Near-surface soil texture information derived from remotely sensed surface soil moisture data could be combined with soil water models to derive the spatial distribution of root zone soil water content at the watershed scale, thereby allowing development of new or improved water resource management tools.