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OpenET project expands availability of water data

Issue Date: September 23, 2020
By Kevin Hecteman

Eyes in the sky and clouds on the ground—of the computing kind—may soon help farmers, ranchers and water managers gain a handle on something they can't see: water vapor.

A web-based program called OpenET is being developed with the goal of providing near-real-time data on evapotranspiration for California and 16 other Western states. The website, set to go live next year, represents a cooperative project by NASA, the Environmental Defense Fund, the Desert Research Institute, the U.S. Geological Survey and the U.S. Department of Agriculture.

The project focuses on evapotranspiration, or ET, the process in which water moves to the atmosphere by evaporation from the land and by transpiration of water vapor from plants. Satellites can track evapotranspiration from orbit, because the process cools plants and soil, making irrigated fields appear cooler.

Justin Fredrickson, environmental policy analyst for the California Farm Bureau Federation, said OpenET promises a range of uses for California farmers, including "water efficiency and precision-farming applications, groundwater sustainability applications, water trading applications, forest management, ecosystem management, water-balance accounting and better water measurement."

Robyn Grimm, senior manager of water information systems for the Environmental Defense Fund, said during a news conference last week that in a world where water-use decision makers are being asked to do more with less, access to reliable information proves critical.

"One of the most important pieces of information for water management in the West, which is the amount of water that's consumed by crops and other vegetation as they grow, has actually been really difficult to attain for the broad majority of folks who are making those decisions on a daily basis," Grimm said.

"Trying to manage water without ET data is like trying to balance or manage your checking account without knowing how much you're spending every day, or knowing where that money is going out," she said.

Its developers said OpenET intends to make use of publicly available data from multiple satellites and weather stations, with the help of the Google Earth Engine platform.

Forrest Melton, a program scientist at the NASA Western Water Applications Office, said multiple models for evapotranspiration data have been developed during the decades by universities and research groups, and they can be "computation-intensive" to run. Earth Engine makes it possible, he said, to run an ensemble of models driven by satellite data.

"For many applications, ET data is most powerful when it's combined with other sources of information," Melton said. "This is especially true for irrigation management. Irrigators have to account for factors including fertilizer and pesticide management, harvest dates and coordination of activities across dozens of irrigation blocks. OpenET will allow farmers and irrigators to access ET data directly from OpenET or via other farm and ranch management software they may already be using."

Eric Averett, general manager of the Rosedale-Rio Bravo Water Storage District in Bakersfield, said implementation of the Sustainable Groundwater Management Act makes developing a water budget imperative. Metering is the most common method of measuring water flow, he added, but can't provide all the needed information.

"Especially in irrigated agriculture, when you meter a well and you apply it to a crop, you have to know how much of the water was actually consumptively used by the tree versus how much was evaporated, and then how much was percolated back into the ground," Averett said. "There's lot of variables that introduce errors."

Measuring evapotranspiration via OpenET, he added, "gives us a very efficient, cost-effective way of accurately metering the amount of water that's consumptively used within the district, without a significant investment in meters and staffing to go out and read them."

He said an online platform developed in partnership with EDF will allow landowners to log in and check their water budgets.

"We think that information is powerful, because it allows landowners to make important decisions with respect to not only just understanding how much water they use, but whether or not they need to reduce or increase," Averett said.

Fredrickson said OpenET's access to data can help dispel an us-versus-them mentality that can arise in water-policy discussions.

"It moves you further out of the land of endless disputes over facts and myths and folklore about how much water farmers are using," Fredrickson said. "It reduces all of these kinds of endless debates to facts."

He added evapotranspiration data represents just one piece in understanding the state's full water picture.

"In California, you have additional complexities relating to separate surface and groundwater components, variables relating to consumptive use, downward percolation and various additional complexities that you have to consider in full, proper context," Fredrickson said. "Easy access to ET is a potentially major new tool in the toolbox—but isn't the whole toolbox."

But, he added, availability of data will be critical.

"In the best of scenarios, rapidly expanding, tech-based info like OpenET can help us to adapt and adjust; remain viable; steward our precious but limited water resources; and manage them in a long-term, sustainable manner, both today and into the future," Fredrickson said.

(Kevin Hecteman is an assistant editor of Ag Alert. He may be contacted at

Permission for use is granted, however, credit must be made to the California Farm Bureau Federation when reprinting this item.

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