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United States Department of Agriculture

Agricultural Research Service

Title: Surface Energy Partitioning over Native and Improved Pastures in the Littlewashita During 1994

Authors
item Prueger, John
item Kustas, William
item Hatfield, Jerry
item Humes, Karen - UNIVERSITY OF OKLAHOMA
item Sauer, Thomas

Submitted to: Agricultural and Forest Meteorology Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: February 2, 1996
Publication Date: N/A

Technical Abstract: Surface energy partitioning on a local scale is an important component of many hydrological studies. In the Little Washita watershed, the land is primarily used as pasture for cattle grazing or as cultivated land for the production of cattle feed. Two types of pastures were characterized as native and improved. Improved pastures were pastures that were converted from native to a Bermuda grass surface. Together native, improved, and cultivated fields formed a patchwork mosaic of ecosystems which make up the dominant portion of the Little Washita watershed. Eddy correlation and Bowen-ratio measurements were made at four sites in the Little Washita Watershed that were representative of the types of topography and vegetative surfaces for the 600 sq. km watershed. The measurements were made for 10 days in early April and for 7 days in mid-August. Energy balance components were compared and evaluated for each of the different surfaces. Evaporative fractions defined as the ratio of latent heat flux to net radiation were calculated and evaluated for each of the ecosystems. Understanding the spatial and temporal dynamics of the evaporative fraction will lead to improvements in regional evapotranspiration models. During early April there was little difference in how the surface energy was partitioned for the native and improved pasture fields. Latent heat fluxes ranged from 50 to 100 W m**-2. Evaporative fractions were also different for each field ranging from 20% for bare soil to 57% for thick native vegetation. The evaporative fraction of each field was found to be relatively stable throughout a typical diurnal cycle.

Last Modified: 11/26/2014
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