Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/28/2002
Publication Date: N/A
Interpretive Summary: The amount of moisture present in soil affects agriculture and engineering, and influences environmental phenomena such as flooding and climate. A better understanding of soil moisture and its distribution in space and time would permit greater control over these important activities and phenomena. Soil moisture content changes as you move across a landscape. The variability arises from a complex interaction of many geophysical parameters such as soil type, topography, vegetation, and climate. A complicating factor is that the relationship between soil moisture and the other parameters changes depending on the space and time scales that you consider. This study was done to improve our understanding of soil moisture and its relationship to land cover and vegetation. Soil moisture data was collected for 3 weeks over 160 acres. Statistical analyses demonstrated the relationship between soil moisture patterns and varying land cover, but also indicated that there was a strong random component to the observed patterns, which was attributed to small-scale variability of geophysical parameters. This work will benefit scientists who are trying to better understand soil moisture and its distribution in space and time.
Technical Abstract: Different factors contribute to soil moisture variability at different space scales and timescales, including soil properties, topography, vegetation, land management, and atmospheric forcings, such as precipitation and temperature. Field experiments supported by adaptive geostatistical and exploratory analysis, including categorical elimination of different governing factors, are needed to bring new insight to this important hydrologic problem. During the Southern Great Plains 1997 (SGP97) Hydrology Experiment in Oklahoma, we investigated the within-season (interseasonal) spatiotemporal variability of surface (0--6 cm depth) soil moisture in a quarter section (800 m by 800 m) possessing relatively uniform topography and soil texture but variable land cover. Daily soil moisture measurements were made between June 22 and July 16 using portable impedance probes in a regular 7 by 7 square grid with 100 m spacings. Initially, the land cover was split between grass and wheat stubble; row tilling on Jun 27 converted the wheat stubble to bare ground. Geostatistical and median polishing schemes were used to analyze the within-season evolution of the spatial structure of soil moisture. The effects of daily precipitation, variable land cover, land management, vegetation growth, and microheterogeneity including subgrid-scale variability were all visible in the analysis. Isotropic spatial correlation range for soil moisture varied between <100 m (for nugget and subgrid-scale variability) and >428 m (for spherical and Gaussian models) within the 4-week-long SGP97 experiment. The findings will be useful for assessing remotely sensed soil moisture data collected during the SGP97 Hydrology Experiment in mixed vegetation pixels.