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On a ranking of states using water for irrigation, seeing California at the top probably wouldn’t surprise you. But would you expect Idaho to follow right behind?

Idaho is roughly half the size of California, with about 20 times fewer people. Yet in a 2015 water census, the U.S. Geological Survey (USGS) estimated that Idaho used more than 15 billion gallons a day for irrigation, compared to almost 19 billion in California and an overall average of less than 1 billion a day for each U.S. state. To say the management of water is important for California and Idaho—indeed, for the entire arid West—would be an understatement.

Idaho is famous as the top potato producer in the U.S. but also ranks high for other crops, such as sugar beets. The State also produces hay for dairy cattle and other livestock. The Snake River Basin of southern Idaho has fertile soil but low rainfall, averaging about 10 inches a year. So farmers there turn to irrigation, with water sourced from a sizable aquifer, Snake River surface water, and large reservoir storage projects in the Upper Snake River system.

Monitoring water use has long been a priority and a challenge for Idaho. But a tool launched in 1972 has given Idaho, other states, the Federal government and even other countries an enduring view of their land and water resources—from more than 400 miles above.

The potential of USGS Landsat satellite data attracted the attention of Idaho officials early on, and the relationship flourishes yet today.

Idaho Embraces Landsat

The use of Landsat data has matured with technology, time, experience, and collaboration.

Color map of evapotranspiration in Idaho in the 2018 growing season
This map, created using Landsat data, shows evapotranspiration for Idaho cropland for the 2018 growing season, indicating irrigation’s consumptive use of water. It was clipped to the bounds of the Idaho Department of Water Resources’ Eastern Snake Plain groundwater model.

The USGS Earth Resources Observation and Science (EROS) Center near Sioux Falls, SD, opened in 1973 to process and archive the data. Dr. Don Lauer arrived in 1974 to help train people to use the data. EROS targeted Federal agencies especially, such as the National Park Service, but also State and international agencies and universities.

However, one challenge States experienced was technical capability. “The States just didn’t have the resources,” Lauer said. “They didn’t have the computer systems to be able to handle anything digital.”

NASA, which builds and launches Landsat satellites, started a program in 1978 involving the USGS and EROS to help promote Landsat applications among State and local governments in the West. The program included a traveling van that offered demonstrations.

The Idaho Department of Water Resources (IDWR) found the demonstration convincing.

Agriculture claims about 90% of the water used in Idaho, according to Phil Blankenau, an evapotranspiration (ET) analyst in the geospatial technology division of IDWR. ET is the movement of water into the atmosphere via evaporation and plant transpiration. Mapping ET can indicate how much surface water or water from an aquifer has been used and will be needed in the future in a particular location, such as an irrigated field.

“Tools like Landsat are very useful for making informed water management decisions that can promote sustainability. The more precisely water can be measured, the more precisely it can be managed,” Blankenau said.

Projects Through the Decades

Initially, IDWR relied on a large IBM 370/168 computer in the auditor’s office to classify land use and examine changes with Landsat data. For example, with data from 1975 and 1980, one early mapping project looked at the conversion in two growing counties from agricultural land to urban area, and another identified where new irrigation had developed in the Big Lost River Basin.

In the mid-1980s, IDWR began the long process of creating a complete and accurate record of water rights on the Eastern Snake Plain. Landsat-derived irrigation maps were developed to avoid the cost of sending staff to physically inventory fields. “It was a huge effort—158,000 water rights were decreed,” Blankenau said.

“There are economic and time-saving benefits to using Landsat, and it also just makes things possible that would be impossible otherwise,” he added.

ET has been a prime focus for IDWR since 2000. A five-year NASA grant led IDWR to partner with Dr. Richard Allen at the University of Idaho to develop an ET mapping process to address water issues. Allen modified an existing European ET model, the Surface Energy Balance Algorithm for Land (SEBAL), to create the Mapping EvapoTranspiration at high Resolution using Internalized Calibration (METRIC) model. Landsat surface temperature data and its resolution of 30 meters are key to the model’s ability to compute ET for individual fields.

Since then, METRIC has been used in projects throughout the West. In Idaho, it has helped with planning for supply and demand of water and has even played a role in determining the outcome of water rights litigation. Idaho’s use of Landsat-based ET data for water administration was recognized in 2009 with the Innovations in American Government Award.

Color photo of irrigated fields near Ashton, Idaho
An irrigation system waters a field near Ashton, Idaho.

Thermal Data Is Key to ET

Lauer, who served as director of EROS from 1992 to 2001, recalled how Idaho’s reliance on thermal data helped influence the design of Landsat 8, which launched in 2013 and currently orbits with Landsat 7. Together, the satellites capture land surfaces around the Earth every eight days.

NASA had proposed removing an expensive new Thermal Infrared Sensor from Landsat 8, thinking the thermal data from Landsat 7 wasn’t being used enough to warrant the expense on the new satellite.

Because surface temperature data is derived from that sensor, “that created a ruckus in Idaho,” Lauer said.

It galvanized IDWR, the Western States Water Council, and Allen at the university to advocate for including the sensor. They rallied other Western States, which had begun realizing the value of thermal data for water applications. The advisory group Landsat Science Team also requested the inclusion of the sensor. As a result, the sensor now orbits on Landsat 8 and will launch with Landsat 9 later this year.

EROS researchers Dr. Gabriel Senay and Mac Friedrichs work extensively with Landsat thermal data in their work with ET. Senay and his team developed an ET model about 15 years ago that has been widely used. Cloud computing now makes possible the effort to expand this Operational Simplified Surface Energy Balance (SSEBop) model across the continental U.S. to help the USGS water census report consistent estimates of water consumption nationwide.

New ET Tool Coming

Of course, interest in ET spreads far beyond government agencies. Individual growers can benefit from knowing whether they’re applying enough irrigation water at a given time. A new web-based platform called OpenET is expected to make that kind of data available to them later this year. OpenET will offer six different ET models—including SSEBop and METRIC—on a cloud-based platform that can also create an ensemble estimate from the different models. The individual models have differentiating features that make certain ones more suitable for certain situations, but the ensemble is expected to reduce the uncertainty and provide a best estimate.

Screenshot of OpenET initiative website
OpenET will allow users to access individual evapotranspiration models to look at water consumption for a particular area, or to get a cumulative assessment using a combination of those models.

Research and improvements continue on the SSEBop model, which in turn will help improve the ensemble version of OpenET, said Senay, who is on the OpenET project team with Friedrichs and Allen from the University of Idaho.

“A large percentage of our water is used by irrigated crops, and that’s why it’s important to accurately quantify the amount of crop water use for improved planning and management. That’s why we strive for getting the ET right—so we can design more efficient irrigation systems. If we reduce our water use by 5%, 10% … we could support many, many cities,” Senay said.

“OpenET provides this great value to states like Idaho who have such a huge irrigation component to their lands and an ET management system that’s so rich in history,” Friedrichs said.

Blankenau appreciates how advances in technology and tools have unlocked an even greater potential than Landsat’s early days.

“It’s just amazing to me that we’ve had decades of Landsat data, and really only recently have tools become accessible to scientists that make it efficient to look at that whole collection,” Blankenau said.

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