NM Tech Scientists Study Remote Sensing of Evapotranspiration in Mountain Areas, Sept. 13, 2006

Hydrology Team

by George Zamora

Photo, right: The New Mexico Tech scintollometer research team, pictured from left to right, Tech student Kim Bandy, Tech hydrology professor Jan Hendrickx, Tech student Whitney Defoor, Tech student Jesus Gomez, and Tech post-doc researcher Jan Kleissl.

SOCORRO, Sept. 13, 2006 – Over the course of the last two decades, hydrologists and other scientists have used emerging technologies such as satellite optical remote sensing to develop and refine several operational evapotranspiration (ET) algorithms that are now routinely used in hydrological studies in New Mexico and worldwide.

However, these remote sensing based algorithms have encountered significant difficulties when used by hydrologists or other water resources professionals to estimate evapotranspiration in mountainous regions because of variability in mountain meteorology, soils, and topography.

In an effort to improve the application of remote sensing algorithms to mountainous terrains, the U.S. Geological Survey recently awarded a research grant to fund a field study in New Mexico, titled “Validation, Calibration, and Improvement of Remote Sensing ET Algorithms in Mountainous Regions.” The multi-year research project is spearheaded by New Mexico Tech hydrology professor Jan Hendrickx, along with Tech post-doctoral researcher Jan Kleissl.

“Up until now, most of the work on evapotranspiration and water usage in New Mexico and elsewhere has focused on riparian areas and agricultural fields, which are relatively flat,” says Hendrickx.

“What we haven’t seen before is an extensive study in mountainous areas where most of the water that makes it down to the flat valley floors comes from,” he adds. “We’ve been focusing on the demand side, but not the supply side of water resources in New Mexico.”

Mountains cover approximately 25 percent of world’s land area, accommodate 26 percent of the world’s population, and generate about 32 percent of surface runoff on a global basis.

However, in New Mexico and other semi-arid mountainous regions, runoff from mountains can represent as much as 90 percent of the total surface runoff into lower-lying basins such as the Rio Grande or Colorado River.

As part of their study, Hendrickx and Kleissl will set up various measuring and recording stations at field sites located atop the Magdalena Mountains and within the Valles Caldera National Park in New Mexico.


The New Mexico Tech hydrologists are using scintillometers — novel scientific instruments that measure atmospheric optical disturbances over distances of up to three miles — to gauge turbulent heat fluxes at mountainous sites. Additional meteorological measurements taken, such as wind speed and direction, surface and air temperature, humidity, and barometric pressure, allow them to examine the determinants of ET in mountainous terrains, thus providing clues to improving ET algorithms there.

In addition, other contributing factors, such as slope, topography, vegetation, solar radiation, and snow accumulation, are being considered by the scientists as they attempt to improve remote sensing ET algorithms.

“Of course, the mountainous terrain itself also contributes to complexities encountered in this study,” says Kleissl. “Driving to and from these field sites to set up stations and obtain measurements can be a difficult challenge, so accessibility becomes a big issue.

“It’s much easier to conduct these types of studies in alfalfa or corn fields, but my undergraduate and graduate research assistants and I are ready to take on the mountains,” he adds.

“In semi-arid regions, such as New Mexico and the rest of the Southwestern United States, evapotranspiration represents the greatest flux of water lost from agricultural fields, riparian areas, forests, rangelands, lakes, and rivers,” Hendrickx states. “It goes up into the atmosphere, and it’s gone.

“Therefore, improving ET estimates in the mountains is crucial for determining the regional water balance, not only in New Mexico and the surrounding region, but also in similar mountainous areas worldwide,” Hendrickx points out.

Several government agencies besides the USGS have already expressed interest in using improved ET algorithms in their water resources planning, including the U.S. Bureau of Reclamation, the Interstate Stream Commission, the New Mexico Office of the State Engineer, and the Middle Rio Grande Conservancy District.

“Our goal is not so much to develop new models or algorithms for how evapotranspiration occurs in mountains as it is to improve current ET algorithms by using an integrated approach that considers the particular features of mountains,” Kleissl says. “These improved ET algorithms will also still be able to be used in flat areas as well.”

In addition to the USGS funding, supplemental support for the ongoing research project currently is being provided by the Water Resources Research Institute, New Mexico Tech, and a National Science Foundation funded program—the Experimental Program to Stimulate Cooperative Research (EPSCoR).