干旱区生态环境知识资源中心

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 significant 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.