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United States Department of Agriculture

Agricultural Research Service

Title: Surface Roughness and Evaporation

Authors
item Sauer, Thomas
item Norman, J. - UNIV OF WISCONSIN-MADISON
item Hatfield, Jerry
item Prueger, John

Submitted to: Western Pacific Australia Geophysics Conference
Publication Type: Proceedings
Publication Acceptance Date: July 15, 1996
Publication Date: N/A

Technical Abstract: In order to accurately estimate surface transfer processes such as evaporation, it is necessary to identify and characterize the controlling factors. Surface-atmosphere interactions are influenced by physical properties of the surface and aerodynamic characteristics of the wind flow. Roughness elements at the surface affects turbulent mixing and, depending on the properties of the elements, may also provide a physical resistance to vapor transfer. The object of this research was to assess the impact of surface roughness on evaporation from soil surfaces with and without a plant canopy. A vapor source plate beneath a maize (Zea mays l.) canopy was used to measure surface transfer coefficients under varying microclimate conditions. Complementary wind tunnel experiments with model roughness elements were used to extrapolate field data to condition with differing levels of roughness. Derived equations based on dimensionless parameters showed that the enhancement of evaporation increased significantly with increasing wind speed inside the canopy. Evaporation measurements were also made in a field of standing maize stubble that remained after harvest of the crop. This stubble provided a sparse array of approximately 0.3-m tall roughness elements with a layer of plant residue on the soil. Over-winter decreases in aerodynamic roughness and wind profile displacement were attributed to compaction of the residue by snow and weathering. Evaporation approached potential rates during much of the fall and spring measurements.

Last Modified: 12/21/2014
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