Online water-use tracker could help Arizona farmers use less on crops

The platform, OpenET, uses satellite data and shows, down to the field level, how much water crops are using week to week. Farmers could compare that to how much water they are applying and reduce the gap between the two.

It is already being used by water districts, tribes, farmers and utilities in the West to track, trade and divert water. In California, it has been used to track compliance with groundwater laws.

Arizona researchers compared the OpenET tool with data taken on-site in alfalfa and cotton fields in the state, and have ongoing trials in wheat and corn crops. The models used in the tool showed great accuracy for alfalfa, but not always for cotton, and the tool would need upgrades to become more useful for farmers, especially those using flood irrigation.

"It's good for looking at previous years and what (water demand) they should expect this year. But it's not ready yet to be used for irrigation management," said Diaa Elshikha, an assistant professor and irrigation specialist at the University of Arizona's Maricopa Agricultural Center, who led the research trials.

In late May, Arizona researchers and OpenET partners held a series of workshops in Maricopa, Willcox and Yuma to introduce growers to the tool, the technology it uses, and how it can be applied in farming operations. The first workshop was attended by four Central Arizona farmers who either participated in the trials or wanted to know how to use the tool.

This kind of open-access information is more important than ever in Arizona, as the state faces a decades-long drought, looming cuts from Colorado River water, and depleting aquifers, researchers said.

“There’s no extra water to be had, even on the best of times,” said University of Arizona Professor Jeff Silvertooth, who has done agricultural research in Arizona for the past four decades. The Colorado River, supplying 40 million people, is overallocated, aquifers are under stress, and climate change could make things even worse, he added.

“This is not a wet-year, dry-year cycle; this is a quarter of a century," Silvertooth said of declining recharge levels in the West's largest reservoirs.

How the tracking tool works

OpenET's maps and data explorer run with data taken from satellites' thermal and optical sensors, which detect cooling from evapotranspiration — how much water is transpiring from plants and evaporating from soil and other land surfaces. With that data, scientists can estimate the water consumed by crops, although not how much water was applied to them.

There is technology that can take this data directly in the field, like the LI-710 used by Arizona researchers in the field, but that equipment is expensive, requires technical expertise, and is limited to the area where it is installed. OpenET has data freely available online for the entire United States.

The FARMS tool was developed through a private-public partnership led by NASA, the Desert Research Institute, California State University, Monterey Bay, the Environmental Defense Fund, and HabitatSeven. Field-scale data is only available for the Western United States and visualized back to 2021, but the nonprofit expects to update the tool to nationwide coverage by the end of the year.

OpenET can tell farmers how much water their crops are using. But it doesn't tell them how much or when they should irrigate next.

That is math they would have to do with other data, such as how much they irrigated in that period, the efficiency of the irrigation system, how much extra water they need to push salts away from the roots, and maybe considerations of soil type, cost of water and crop prices. This is not available in the OpenET FARMS tool. But because the whole platform is open-access, researchers, companies and app developers can create tools that make this math and serve users better.

At this time, OpenET serves more for retrospective than for everyday decisions. How much water did a crop use in the middle of the summer? How much water was applied? How can I adjust my irrigation next year?

Less useful for farms that could save the most water

The math for everyday decisions on how to water crops is easier to do and to apply for farmers already using efficient irrigation methods. For farmers using center pivot irrigation, an elevated pipe system that creates crop circles, or drip irrigation, a system of thin tubes that water plants drop by drop, weekly data from the tool can be enough to make changes. If OpenET says the plant is only using a certain amount of water and the farmer knows they applied more than that, they can adjust the next irrigation date, for example.

Flood irrigation is a cheaper but slower and more water-intensive process. Canals and ditches take water to the fields, and it flows by gravity from one border, or furrow, of the farm plot to the next. The whole farm is not irrigated simultaneously but split into "irrigation sets" and watered one section at a time, Elshikha said, adding that "a full irrigation cycle can take anywhere from a few hours to several days."

Because of how the system is set up, it's hard to skip watering one plot or do different irrigation times on each section.

OpenET makes estimates from data collected every eight days by the satellites, but it will soon produce daily estimates for the FARMS tool, using weather and land-surface data. Because the daily values are not direct measurements, they carry more uncertainty, Elshikha said. Even with daily data, water savings in flood irrigation, where savings are needed the most, would be minimal.

"The timing is much harder to adjust," said Ross Rayner, a partner at Tumbling T Ranch and a young fourth-generation farmer in Goodyear. Arizona researchers evaluated the OpenET tool on his farm, comparing it to on-site data. Because a lot of Rayner's land is under center pivot irrigation, the operation is nimbler to make changes on how and when to water. Flood irrigated fields are less flexible in that way, he said.

Converting farms to more modern and efficient irrigation systems is a simple solution to water savings, but there are many reasons why it isn't easy in Central Arizona. Flood irrigation is the only way that farmers can push accumulated salts away from plant roots. The investment in new irrigation technology and the costs of water pumping are prohibitive to many farmers, and canal systems would need to be adapted for drip irrigation with ponds and filtration systems.

Overall, Arizona has about 920,000 acres of irrigated farmland, and 75% of it is irrigated by "gravity," according to the latest U.S. Department of Agriculture irrigation and water management survey. About 10% is irrigated with a form of drip.

Some conversions to other systems have been paid for with state money. The UA's Water Irrigation Efficiency program, with a total funding of $46.2 million, partially reimbursed farmers for switching to a more efficient irrigation method. Nearly 21,500 acres have been converted to date with the help of the program.