Abstract
Surface soil moisture content is a state variable that is either simulated or required as input for many hydrologic models. In distributed hydrologic modeling, the watershed system is subdivided into spatial elements that should be as homogeneous in hydrologic response as possible. In this study, the variation of surface soil moisture was examined because soil moisture is a major factor in determining hydrologic response. The influence of variations in land cover, soil properties and topography on surface soil moisture was investigated. Statistical analysis showed that topography was the most important factor controlling the distribution of soil moisture within the small agricultural watersheds at Chickasha, Oklahoma. The presence of vegetation tends to diminish the soil moisture variations caused by topography, while the effects of minor variations in soil type were usually insignificant. Comparison of variograms developed for nearly flat cropland water-sheds and more sloping rangeland watersheds indicated that a much denser network of sampling points would be required to develop soil moisture maps of a given accuracy on the rangeland watersheds. For many modeling purposes, the subdivision of low-slope cropland watersheds into spatial units of homogeneous hydrologic response can be based on topography alone.
Published Version
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