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United States Department of Agriculture

Agricultural Research Service

Title: Evaluation of Multiple Flux Measurement Techniques Using Water Balance Information at a Semi-Arid Site 1198

Authors
item Houser, P. - NASA, GODDARD
item Harlow, C. - UNIV. OF ARIZ.
item Shuttleworth, W. - UNIV. OF ARIZ.
item Keefer, Timothy
item Emmerich, William
item Goodrich, David

Submitted to: American Meteorological Society
Publication Type: Proceedings
Publication Acceptance Date: January 13, 1998
Publication Date: N/A

Interpretive Summary: Water is the key to life in arid and semi-arid regions. In order to manage both agriculture and municipal development, as well as minimize our impacts on the environment in these regions we must have better knowledge of the quantities and pathways of water. One of the biggest losses of rainfall water in these regions is through evaporation and transpiration (ET) from desert vegetation. However, it is difficult to measure ET over varied landscapes and over mixed plant types. An experiment was carried out in southeastern Arizona during the summer of 1996 which compared five different instruments used to measure ET of a desert mixed-shrub area. Each of these methods varies widely in terms of cost and complexity. In addition to the five instruments, ET was measured by computing the difference between rainfall, runoff and the change in water in the soil (water balance). It was found that ET measured by the different methods varied substantially with most of them overestimating ET as measured by th water balance. The results provide estimates of the accuracy of ET measurements in terms of the cost and effort required to make them.

Technical Abstract: A month-long field experiment was performed at the Lucky Hills Metflux site in the Walnut Gulch Experimental Watershed during the 1996 summer rainy season to evaluate multiple surface water and energy flux measurement techniques using detailed water balance information. Five different surface flux instruments were deployed between July 14 and August 21, 1996. .These instruments included a propeller eddy covariance system, a sonic anemometer and infrared gas analyzer based eddy covariance system, a infrared gas analyzer based Bowen ratio system, and two temperature variance systems. The water balance was computed using precipitation measured in 7 nearby rain gauges, flume measured subcatchment runoff, and root zone soil moisture measured using Time-Domain Reflectometry (TDR). Based on the water balance, most of the surface water and energy flux measurement instruments overestimated the evapotranspiration, and there was ssignificant inter-instrument variation. Some of the observed differences may be due to fetch heterogeneity or instrument limitations, however there may also be issues regarding the application of these instruments and their associated measurement theory in this environment.

Last Modified: 11/23/2014
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