Submitted to: Advances in Water Resources
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2012
Publication Date: 12/1/2012
Citation: Cosh, M.H., Evett, S.R., McKee, L.G. 2012. Surface soil water content spatial organization within irrigated and non-irrigated agricultural fields. Advances in Water Resources. 50:55-61.
Interpretive Summary: Remote sensing and in situ monitoring of surface soil water content currently operate on two different scales. Most remote sensing platforms have a spatial resolution of several kilometers, while in situ measurements have a scale on the order of several centimeters. This disparity requires a methodology for scaling, so that the remote sensing product can be validated. During a field experiment in a heavily instrumented field in Bushland, Texas, a series of intensive measurements were made to charactize soil moisture from the measurement scale to the field scale. This work intended to bridge this scale gap. Several conclusions were drawn from this work, including that the tillage aspects of the field have an impact on the variability of soil water content, and the distribution can be approximated by a power law distribution. This implies that this is a considerable amount of correlation for soil moisture between the scales being studied as well as temporal stability. It is concluded that the soil water content can be easily scaled with a series of short scaling campaigns which will allow small scale measurements to accurately represent a remote sensing footprint.
Technical Abstract: Understanding soil water content variability is important for monitoring and modeling of land surface processes as well as land and water management practices. With regards to in situ probes, it is sometimes assumed that a single local measurement can represent the larger domain, mostly for practical reasons. But there is a substantial amount of variability in soil water content at the field scale. As part of the BEAREX08 campaign, a high-density sensor network and intensive observational periods were developed to fully describe the soil water conditions at the surface on the field scale, in support of the hydro-meteorological measurements being collected. A total of 20 soil water content stations were distributed over an irrigated and a non-irrigated field (~10 ha each) and high-density (~every 5 cm) transects were measured for a high-detailed record. The network was able to provide accurate large scale estimates of soil water content with a root mean square error of 0.035 cubic meter per cubic meter. The network was temporally stable with the exception of irrigation events, which caused significant increases in coefficients of variation due to the length of time necessary to irrigate the entire field. The spatial distribution of surface soil water content was significantly affected by the row structure of the cotton plants, which was North-South in the field where transect measurements were made with a row spacing of 30 cm. At scales less than 30 cm, the distribution was closely correlated in the East-West direction. For scales larger than 30 cm in the East-West direction the correlation decreased, but was still present. In the North-South direction this discontinuity was not present, and soil water content followed a power law distribution.