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Title: EVAPOTRANSPIRATION ON WESTERN U.S. RIVERS ESTIMATED BY REMOTE SENSING AND EDDY COVARIANCE FLUX TOWER DATA 1762

Author
item NAGLER, P. - UNIVERSITY OF ARIZONA
item Scott, Russell - Russ
item CLEVERLY, J. - UNIVERSITY OF NEW MEXICO
item WESTENBURG, C. - USGS
item GLENN, E. - UNIVERSITY OF ARIZONA
item HUETE, A. - UNIVERSITY OF ARIZONA

Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: 2/1/2005
Publication Date: 5/23/2005
Citation: Nagler, P., Scott, R.L., Cleverly, J.R., Westenburg, C., Glenn, E.P., Huete, A.R. 2005. Evapotranspiration on western u.s. rivers estimated by remote sensing and eddy covariance flux tower data. Trans. AGU, 86(18), Jt. Assem. Suppl., Abstract H23B-08

Interpretive Summary: Evapotranspiration (ET) rates measured from eight eddy covariance flux towers on three western United States rivers were highly correlated with Enhanced Vegetation Index (EVI) values from Moderate Resolution Imaging Spectrometer sensors on the NASA Terra satellite. Sixteen-day composite values of EVI and maximum daily air temperature (Ta) were combined to predict ET across species and sites (r2 = 0.76). The relationship was then used to estimate ET for 2000-2004 over large river stretches on the Upper San Pedro River, the Middle Rio Grande, and the Lower Colorado River. EVI and ET values were similar across river systems. Measured and estimated ET values tended to be moderate when compared to earlier, and often indirect, estimates, and ranged from 850-1,060 mm yr-1. EVI for individual plant associations, used as a measure of relative ET rates, ranked cottonwood (Populus spp.) and willow (Salix spp.) highest, mesquite (Prosopis glandulosa) and saltcedar (Tamarix ramosissima) intermediate, and giant sacaton (Sporobulus wrightii) and arrowweed (Pluchea sericea) lowest in potential ET. However, saltcedar EVI had a high variance, as this species can grow in sparse to dense stands, depending on water availability. ET rates estimated by remote sensing in this study produced similar values as direct, ground-based measurements on the San Pedro River, but they were much lower than official values estimated for riparian water budgets using crop coefficient methods for the Middle Rio Grande and Lower Colorado River.

Technical Abstract: Evapotranspiration (ET) rates measured from eight eddy covariance flux towers on three western United States rivers were highly correlated with Enhanced Vegetation Index (EVI) values from Moderate Resolution Imaging Spectrometer sensors on the NASA Terra satellite. Sixteen-day composite values of EVI and maximum daily air temperature (Ta) were combined to predict ET across species and sites (r2 = 0.76). The relationship was then used to estimate ET for 2000-2004 over large river stretches on the Upper San Pedro River, the Middle Rio Grande, and the Lower Colorado River. EVI and ET values were similar across river systems. Measured and estimated ET values tended to be moderate when compared to earlier, and often indirect, estimates, and ranged from 850-1,060 mm yr-1. EVI for individual plant associations, used as a measure of relative ET rates, ranked cottonwood (Populus spp.) and willow (Salix spp.) highest, mesquite (Prosopis glandulosa) and saltcedar (Tamarix ramosissima) intermediate, and giant sacaton (Sporobulus wrightii) and arrowweed (Pluchea sericea) lowest in potential ET. However, saltcedar EVI had a high variance, as this species can grow in sparse to dense stands, depending on water availability. ET rates estimated by remote sensing in this study produced similar values as direct, ground-based measurements on the San Pedro River, but they were much lower than official values estimated for riparian water budgets using crop coefficient methods for the Middle Rio Grande and Lower Colorado River.