Determining Evapotranspiration Rates in the Middle Rio Grande Bosque: 3-D Eddy Covariance and Remote Sensing Techniques

Currently, annual rates of actual evapotranspiration (ET) in native and non-native riparian forests in semi-arid landscapes are poorly known. In addition, the effects of flooding, or the removal of flooding through flow regulation, on riparian ecosystem ET is also not well understood. Both ground-based and remote sensing techniques are used to estimate ET along the Middle Rio Grande corridor. Ground based climatic data are collected using four instrumentation towers installed in representative ecosystems. The 3-D Eddy Covariance method gives more accurate estimates of ET than were previously known. Landsat imagery, along with ground estimates of leaf area index (LAI), will be used to scale the estimates to the entire corridor. Background Evapotranspiration is believed to account for about one quarter of the total water depletion along the semi-arid Middle Rio Grande Valley, New Mexico. An accurate estimate of evapotranspiration (ET) is an important component in developing effective riparian restoration strategies for this area, as well as for better quantifying the water budget. The Middle Rio Grande runs through central New Mexico, U.S.A. and is typically defined by the reach of river between Cochiti Dam and Elephant Butte Reservoir. The contributing watershed to this reach of river is shown in Figure 1. Water demands include those of the state’s largest city (Albuquerque), irrigation districts, and several endangered species. Water budgeting is critical due to these demands and the legal compacts between adjacent states requiring the delivery of mandated quantities of water. The inputs and outputs of water from the upper and lower end of the river corridor are reasonably well quantified by permanent gauges with long-term records. Additional sources of water along the Middle Rio Grande corridor, and the amount of water depleted by various sources, are more poorly quantified.