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AGRICULTURAL
<br />AND
<br />FOREST
<br />METEOROLOGY
<br />ELSEVIER Agricultural and Forest Meteorology 105 (2000) 281 -309
<br />www.cisevier.com/kvAte/agrfoniiet
<br />Seasonal estimates of riparian evapotranspiration
<br />using remote and in situ measurements
<br />D.C. Goodricha, *, R. Scott', J. Qic, B. Goffa, C.L. Unkricha, M.S. Morana,
<br />D. Williams', S. Schaefferd, K. Snyder', R. MacNish', T. Maddock',
<br />D. Pool e, A. Chehbouni f, D.I. Cooper g, W.E. Eichinger h,
<br />W.J. Shuttleworth', Y. Kerr', R. Marsett a, W. Ni a
<br />a USDA ARS, Southwest Watershed Research Center, Tucson, AZ 85719, USA
<br />b University of Arizona, Tucson, AZ, USA
<br />Michigan State University, East Lansing, MI, USA
<br />d University of Arkansas, Fayetteville, AR, USA
<br />US Geological Survey, Water Resources Division, Tucson, AZ, USA
<br />f IRDIIMADES, Hermosillo, Sonora, Mexico
<br />B Las Alamos National Laboratory, Las Alamos, NM, USA
<br />h University of Iowa, Iowa City, IA, USA
<br />' CESBIO, Toulouse, France
<br />Abstract
<br />In many semi -arid basins during extended periods when surface snowmelt or storm runoff is absent, groundwater constitutes
<br />the primary water source for human habitation, agriculture and riparian ecosystems. Utilizing regional groundwater models
<br />in the management of these water resources requires accurate estimates of basin boundary conditions. A critical groundwater
<br />boundary condition that is closely coupled to atmospheric processes and is typically known with little certainty is seasonal
<br />riparian evapotranspiration (ET). This quantity can often be a significant factor in the basin water balance in semi -arid regions
<br />yet is very difficult to estimate over a large area. Better understanding and quantification of seasonal, large -area riparian ET
<br />is a primary objective of the Semi -Arid Land- Surface - Atmosphere (SALSA) Program. To address this objective, a series of
<br />interdisciplinary experimental campaigns were conducted in 1997 in the San Pedro Basin in southeastern Arizona. The ripar-
<br />ian system in this basin is primarily made up of three vegetation communities: mesquite (Prosopis velutina), sacaton grasses
<br />(Sporobolus wrighth), and a cottonwood (Populus fremontii) /willow (Salix goodingii) forest gallery. Micrometeorological
<br />measurement techniques were used to estimate ET from the mesquite and grasses. These techniques could not be utilized to
<br />estimate fluxes from the cottonwood/willow (C /W) forest gallery due to the height (20-30 m) and non - uniform linear nature
<br />of the forest gallery. Short-term (24 days) sap flux measurements were made to estimate canopy transpiration over several
<br />periods of the riparian growing season. Simultaneous remote sensing measurements were used to spatially extrapolate tree
<br />and stand measurements. Scaled C/W stand level sap flux estimates were utilized to calibrate a Penman— Monteith model to
<br />enable temporal extrapolation between synoptic measurement periods. With this model and set of measurements, seasonal ri-
<br />parian vegetation water use estimates for the riparian corridor were obtained. To validate these models, a 90 -day pre- monsoon
<br />water balance over a 10 km section of the river was carried out. All components of the water balance, including riparian ET, were
<br />*Corresponding author.
<br />0168 - 1923/00/$ — see front matter Published by Elsevier Science B.V.
<br />PII: SO 168-1923(00)00197-0
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