New method for measuring evapotranspiration

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Bump and update: Here’s the release from the USGS (Ron Beck):

Data from earth-observing Landsat satellites plays a central role in a new, award-winning type of mapping that tracks water use.

Water-use maps help save taxpayer money by increasing the accuracy and effectiveness of public decisions involving water – for instance, in monitoring compliance with legal water rights. The maps are especially important in dry western states where irrigated agriculture accounts for about 85 percent of all water consumption.

Using Landsat imagery supplied by the U.S. Geological Survey in combination with ground-based water data, the Idaho Department of Water Resources and the University of Idaho developed a novel method to create water-use maps that are accurate to the scale of individual fields. The Ash Institute at Harvard University recently cited Idaho’s original design for these maps as an outstanding innovation in American government.

“The USGS Landsat archive, dating back to1972, has proven to be a versatile source of consistent data about land surface conditions,” said Bryant Cramer, USGS Associate Director for Geography. “This advance by the Idaho water monitoring team is both brilliant and practical. Looking forward, it’s indicative of what researchers in many countries can accomplish with the data.”

The value of the USGS Landsat archive was endorsed by Richard Allen of the University of Idaho, one of the honored team members. “Archival support from USGS gave Idaho researchers the means to determine changes in water consumption over time by agricultural, residential and wildland systems,” he said. “These historical records were indispensable in calibrating many aspects of current data.”

As agricultural irrigation needs and swelling city populations amplify demand for scarce water supplies, water management strategy has been forced to shift from increasing water supply to more effectively managing water use at sustainable levels. Thus, accurate water-use mapping is critical. The Landsat-based method can be as much as 80 percent more accurate than traditional measurement methods.

With initial assistance from NASA, the Idaho Department of Water Resources began cooperating with the University of Idaho in 2000 to develop a computer model, METRIC (Mapping EvapoTranspiration at high Resolution with Internalized Calibration), to estimate and map water use in vegetated areas. The mapping method has since been adopted in other states including Montana, California, New Mexico, Utah, Wyoming, Texas, Nebraska, Colorado, Nevada and Oregon.

The objective nature of the technique assists these states in negotiating Native American water rights, assessing urban water transfers, managing aquifer depletion, monitoring water right compliance, and protecting endangered species. Internationally, Spain, South Africa and Morocco have already begun to employ Landsat-based water-use maps.

“I congratulate Richard Allen, Anthony Morse, William Kramber and their Idaho colleagues on their inventive work. The recognition of this prestigious award is well deserved,” Cramer said.

“I believe this success is a marker for more to come,” he continued. “The USGS policy of releasing the full Landsat archive over the Internet at no cost opens the door to a much larger pool of researchers worldwide. More researchers will lead to even more data applications that tackle major environmental issues.”

From The Washington Post (Kari Lydersen):

Using surface temperature readings from government satellites, air temperature and a system of algorithms, the new method lets officials measure how much water is “consumed” on a certain piece of land through evapotranspiration.

Evapotranspiration is a combination of the evaporation of water into the atmosphere and the water vapor released by plants through respiration — basically, a measurement of the water that leaves the land for the atmosphere, not water that is diverted or pumped onto land but then returned quickly to the water table or river for other users.

Water resource management agencies in Idaho and other states see this as the best way to measure water consumption, since it is a more exact definition of how much water is being removed from the system by a given individual or entity. The program, called METRIC for Mapping EvapoTranspiration with High Resolution and Internalized Calibration, was launched in 2000 with a NASA/Raytheon Synergy Project grant and is used by 11 states. (Though researchers do measure the evapotranspiration rates of residential developments, the method is mainly relevant to the management of agriculture, fish farms and forest or wetland conservation.)

“There’s not enough water for all uses, so you use METRIC to see exactly where water is being consumed,” said Tony Morse, manager of geospatial technology at the Idaho Department of Water Resources. “How much for agriculture, how much on the Indian reservation, how much by native cottonwoods, how much by saltcedars.”

METRIC uses images from the two Landsat satellites, which orbit Earth every 16 days, meaning an image of a given field is available every eight days unless cloud cover interferes. Until this year users had to pay the U.S. Geological Survey $600 for each 185-by-180-kilometer “scene.” Starting in 2009 the government satellite images, which are also used for Google Earth, are free to the public. METRIC developers have published their algorithms for anyone to use, though agencies must write their own computer codes.

The data have already been used to help settle a century-long fight between Colorado and Kansas over water in the Arkansas River and a dispute between Idaho irrigation districts. Previously, officials had to look at well-pumping records and electricity use to estimate each irrigation district’s usage. Water managers say the data help to settle and avoid litigation.

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