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The OpenET project will enable farmers and water managers in arid western states to accurately track water consumption by crops and other vegetation through a web application that uses data from satellites and weather stations.

Evapotranspiration—the ET in OpenET—is the process by which water is transferred from the land to the atmosphere through evaporation from land surfaces and transpiration from plants. ET can be tracked by satellites because the energy transfer process cools plants and soil down, so irrigated fields appear cooler and greener in satellite images.

“Our primary goal is to make sure we are providing evapotranspiration data that is accurate, consistent, scientifically based and useful for water management, whether for an individual agricultural field or an entire river basin,” said Forrest Melton, program scientist for the NASA Western Water Applications Office.

Today, access to accurate, timely satellite-based data on the amount of water used to grow food is fragmented and often expensive, keeping it out of the hands of many farmers and decision-makers. Water supplies in the western U.S. are critical to the health of communities, food supply and wildlife, but are facing increasing pressures in the face of population growth and a changing climate.

Starting in 2021, OpenET will make results for six different ET models widely accessible to users on a single web-based platform. By placing the individual algorithms and data for each model into Google’s cloud-based Earth Engine platform, OpenET will enable users to decide which model or models best address their water consumption information needs. Or, they can use an ensemble value that represents a scientific consensus view of the most accurate estimate for that location and time interval. In either case, users will be able to access valuable information about water consumption all the way down to the field level.

OpenET will also make it possible to track the amount of evapotranspiration reduced when farmers change cropping patterns, invest in new technologies, or adopt water-saving practices. Initially, OpenET will provide field-scale ET data in 17 states: Arizona, California, Colorado, Idaho, Kansas, Montana, Nebraska, Nevada, New Mexico, North Dakota, Oklahoma, Oregon, South Dakota, Texas, Utah, Washington ,and Wyoming.

Remote sensing combined with ground-based weather data is the only way to estimate actual ET over large areas and over long time periods— a fact that motivated USGS Scientist Gabriel Senay and his colleagues at the Earth Resources Observation and Science (EROS) Center to develop an operational ET model called the Operational Simplified Surface Energy Balance (SSEBop) model, which is one of the six models that are part of OpenET.

The contributions of USGS and EROS have been important, said Justin Huntington, a research professor at DRI and member of the USGS-NASA Landsat Science Team. DRI and EROS staff sketched out how to use the SSEBop model on Google Earth Engine, Huntington said, but did so in a way that any model could be plugged into it, scaled, and run on it. “The collaboration with USGS EROS really helped us develop the bones of this framework,” Huntington said.

Melton said OpenET wanted to include models that were either being used operationally by states or Federal agencies, or were advancing toward operational use. “Having SSEBop, as Justin pointed out, was helpful as one of the first models to be implemented in Earth Engine and run for a full year at scale,” Melton said. “But it is also ... as a core part of the National Water Census, is really important, too.”

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OpenET is being made possible by the collaborative efforts of an OpenET team that includes Environmental Defense Fund (EDF), NASA, the Desert Research Institute (DRI), U.S. Geological Survey (USGS), U.S. Department of Agriculture (USDA), Google, and leading scientists at California State University Monterey Bay, the University of Idaho, the University of Maryland, the University of Nebraska-Lincoln, and the University of Wisconsin-Madison.

Some of the applications of OpenET data will include:

• Informing irrigation management and scheduling practices to maximize “crop per drop” and reduce costs for water and fertilizer;
• Enabling water and land managers to develop more accurate water budgets and innovative management programs that promote adequate water supplies for agriculture, people, and ecosystems;
• Supporting groundwater management, water trading, and conservation programs that increase the economic viability of agriculture across the West.

“We envision OpenET leveling the playing field by providing all farmers with data that until now have not been widely accessible to everyone,” said EDF’s Robyn Grimm, senior manager for water information systems.

OpenET data also provide a way to track and give credit for past and future water conservation efforts, Grimm said. The data can help growers or landowners quickly assess year-over-year water savings resulting from previous or new investments in conservation. The platform can also help users better understand how water is being used in a system, identify stress, and advance sustainable resource management practices at larger scales than are currently possible.

In time, OpenET could prove useful beyond the western U.S., as well, Huntington said. “We also see OpenET having the potential to scale up to other regions of the world, including South America and Africa,” he said.

OpenET is being developed with input from more than 100 stakeholders around the West, and leading U.S. scientists in the field of remote sensing of ET. The OpenET project has received funding from the NASA Applied Sciences Program Western Water Applications Office, S.D. Bechtel, Jr. Foundation, Gordon and Betty Moore Foundation, Walton Family Foundation, Water Funder Initiative, Lyda Hill Philanthropies, Delta Water Agencies, and the Windward Fund. In-kind support has been provided by Google Earth Engine, Water Funder Initiative, and partners in the agricultural and water management communities.

While providing farmers and local water managers free ET data is a core objective of the OpenET project, for-profit entities and other organizations looking for large-scale access to OpenET data will be able to purchase it through an application programming interface (API). Revenue generated will fund continuing research and development of OpenET data services.

Log on to the OpenET website to learn more about the initiative.