Evapotranspiration at the land/water interface in a semi-arid drainage basin

1. Evapotranspiration (ET) is a major source of water depletion from riverine systems in and and semiarid climates. Water budgets have produced estimates of total depletions from riparian vegetation ET for a 320-km reach of the Middle Rio Grande, New Mexico, U.S.A., that have ranged from 20 to 50% of total depletions from the river. 2. Tower-based micrometeorological measurements of riparian zone ET throughout the growing season using three-dimensional eddy covariance provided high quality estimates of ET at the stand scale. 3. A dense stand of salt cedar (111-122 cm year(-1)) and a mature cottonwood (Populus deltoides ssp. wislizenia Eckenwelder) stand with an extensive understory of salt cedar (Tamaria ramosissima Ledeb) and Russian olive (Eleagnus angustifolia L.) (123 cm year(-1)) had the highest rates of annual ET. A mature cottonwood stand with a closed canopy had intermediate rates of ET (98 cm year(-1)). A less dense salt cedar stand had the lowest rates of ET (74-76 cm year(-1)). 4. Summer leaf area index (LAI) measurements within the four stands were positively correlated with daily ET rates. LAI measurements throughout the growing season coupled to riparian vegetation classification is a promising method for improving riverine corridor estimates of total annual riparian zone ET along a reach of river. 5. Combining recent estimates of the extent of riparian vegetation along the 320 km length of the Middle Rio Grande, from Landsat 7 imagery with annual growing season measurements of ET at the four riparian stands yields a first-order riverine corridor estimate of total riparian zone ET of 150-250 x 10(6) m(3) year(-1). This is approximately 20-33% of total estimated depletions along this reach of river.