ARS | Publication request: USING TEMPORAL PERSISTENCE TO UPSCALE SOIL WATER CONTENTS AND REDUCE UNCERTAINTY

Submitted to: American Geophysical Union
Publication Type: Abstract
Publication Acceptance Date: September 8, 2005
Publication Date: November 5, 2005
Citation: Guber, A.K., Gish, T.J., Pachepsky, Y.A., Nicholson, T.J., Cady, R.E. 2005. Using temporal persistence to upscale soil water contents and reduce uncertainty. American Geophysical Union Fall Meeting, December 5-9, 2005, San Francisco, CA, Paper No. H43C-06.

Technical Abstract: When a field plot or a small watershed is repeatedly surveyed for soil water contents, locations can often be identified where soil is consistently wetter or dryer than the average across the surveyed area. The objective of this work was to upscale water contents from point measurements to the field scale. To accomplish this, a technique was developed using temporal persistence of soil water contents to reduce uncertainty in the average water contents. 24 soil moisture multi-sensor capacitance probes were installed to monitor water content across a 6 ha area at the USDA-ARS OPE3 site in Beltsville, MD. These probes were located at depths of 10, 30, 50, 80, 120, 150, and 180 cm and were monitored every 10 min for 610 days. To quantify the temporal persistence, hourly average water content was computed for all probe readings at one depth. Then the relative water contents were computed as ratios of the individual-probe water content measurement to the average water contents at that same depth (i.e. 10 cm depth). Based on these calculations, it appears that temporal persistence of soil-water contents was well pronounced at certain probe locations. For example, the distribution of relative water content covered a narrow range (e.g., 0.8 to 1) for the location N20. Median relative water contents were used to estimate missing data or correct errant sensor readings, thus substantially reducing uncertainty in average water content across the study area. Relative water contents also enabled reducing the number of sensors needed to obtain a specified accuracy of the average water content estimates. One month of soil moisture monitoring was found sufficient to evaluate distributions of the relative water contents and thus to determine temporal persistence. Using temporal persistence was a useful means to upscale water contents and reduce uncertainty.