Water Measured From the Sky
Satellites Track Land's Consumption
Monday, September 14, 2009
Water management is serious business in the American West, where precipitation is scarce, irrigated agriculture is a major industry, new housing subdivisions spread across arid landscapes and water rights are allocated in a complicated seniority system.
"If you can't measure it, you can't manage it," water officials are fond of saying.
But measurement -- trying to determine how much water is diverted from rivers and how much is pumped from hundreds of thousands of wells -- has been an inexact and expensive science.
Now a tool developed by the Idaho Department of Water Resources and the University of Idaho is changing the face of water management and conservation by efficiently offering specific measurements of the water consumed across a large region or single field.
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.
"This tool would allow the state of Wyoming or Colorado to independently verify what's going on in California," said Tony Willardson, executive director of the Western States Water Council. "It probably wouldn't be safe for someone in a Colorado Department of Natural Resources truck to drive around in California to see how much water they're using."
In Oregon, METRIC data helped conserve water in Klamath Basin salmon habitats by helping scientists work with ranchers to withhold irrigation from certain cattle pastures. In California, the program eased fears that water transfers to Los Angeles and San Diego would increase the salinity of Imperial Valley farmland. In Texas, METRIC revealed that invasive saltcedar trees were using less water than expected, indicating an expensive eradication of the trees was likely not necessary.
Willardson said the system can allow irrigation districts or other entities to conserve water and save the surplus for drier times. For example, if Southern California's Imperial Valley irrigation district can prove that it used less water than it has rights to, it can use more water from the Colorado River the following year. In the past, Imperial Valley farmers would have had little incentive not to use their full water rights.
The same principle applies to farmers who can "bank" their rights to consumer water and lease or sell those rights to other users. The data are also crucial to government programs that buy back water rights -- essentially paying farmers to let their land dry -- so the water can flow into streams where steelhead trout and salmon spawn.
Recently the program's future has been in jeopardy because NASA was not planning to include the $100 million thermal infrared sensor needed to record surface temperature in the next Landsat satellite, scheduled to launch in 2012. The currently orbiting Landsat 5 and 7 were launched in 1984 and 1999 and were designed to last only three to five years.
After much pressure from Western politicians, it appears NASA will include the sensor in Landsat 8. A final decision is expected by the end of the year, according to Jim Irons, a project scientist for the Landsat Data Continuity Mission based at the Goddard Space Flight Center in Maryland.
"Due to their demonstration of the value of the data, we are doing our utmost to make sure we can include the instrument," Irons said.
The project is a finalist for the Harvard Kennedy School's Innovations in American Government Awards, to be announced Monday. James Levitt, director of the Program on Conservation Innovation at the Harvard Forest, Harvard University, said METRIC is among the most remarkable of hundreds of applications he has reviewed. He thinks it will help Western states adapt to climate change, as more extreme heat and less precipitation are expected.
"The water conflicts that are brewing are intense," he said. "If you don't have water you can't farm. Climate change is actually happening now. This will allow government and farmers to adapt. Not every farmer in Idaho subscribes to global warming as a proven theory. But they want to know where their water is."