University of Idaho and state Department of Water Resources researchers will test the accuracy of a new automated tool that interprets satellite imagery to help farmers and water managers track daily water consumption by crops.

OpenET software takes thermal imagery from NASA Landsat satellites and maps daily and cumulative evapotranspiration over the growing season. Growers can study variability within irrigated fields, such as in different areas irrigated by pivot sprinkler.

Evapotranspiration includes evaporation and transpiration, which is movement of water from soil to the atmosphere via plants, according to the U.S. Geological Survey. Transpiration occurs when plants take up water and release vapor into the air from leaves.

The state Water Resource Board awarded UI agricultural engineering professor Erin Brooks about $800,000 over three years to test and calibrate OpenET.

Tracking evapotranspiration will inform growers of the amount of water their crops are using compared with the amount they are applying to their fields through irrigation equipment, helping them to improve efficiency, according to a UI news release.

“It helps growers in the sense that they can actually go in and see what happened, and they can actually evaluate their water-use efficiency — something they’ve never been able to do before on a field-by-field basis,” Brooks said. And it helps the Idaho Department of Water Resources “know what has gone on and whether curtailments have made a difference.”

“If we don’t see a difference in evapotranspiration after a curtailment in an area, that means the growers are more efficient with how they use the water, and it ultimately doesn’t help maintain the minimum flows” in the Snake River, he said. “That consumptive water use has to go down in order to have more water at the outlet.”

State law defines consumptive use as diverted water that does not return to the system due to transpiration, evaporation or conversion to vapor.

Accurate quantification of evapotranspiration “is critical to basin-scale water budgets and sustainable water management in Idaho,” Phil Blankenau, an IDWR evapotranspiration analyst, said in the release.

The department has been using UI-developed software that requires trained staff to run imagery to produce evapotranspiration data. UI also aided in developing the beta version of the automated OpenIT.

Researchers this fall will place soil moisture sensors and eddy covariance towers — which take various ground-based, site-specific meteorological readings — near three south-central Idaho fields to record baseline evapotranspiration data. The team will include data from a separate project on farm fields at the future site of the university’s Idaho Center for Agriculture, Food and the Environment near Jerome.

By comparing data from the sensors and towers with data from OpenET, researchers aim to determine any adjustments needed to improve the automated system’s performance.

Water Resources’ initial testing of OpenET “suggests there may be some errors introduced in the automated approach,” Brooks said. Developers are “interested in evaluating the accuracy of the new tool and potentially developing approaches to correct any errors that may be revealed by the project.”