In a new study published in 'Agricultural Water Management' on August 8, DRI scientists compared groundwater meter data with OpenET estimates for fields in Nevada and Oregon. Their findings show that OpenET can accurately estimate groundwater used for irrigation at the level of individual fields. This is the first study to track water from a well to a field and assess how much of it is absorbed by crops, providing valuable insights into irrigation efficiency. The researchers believe the method can support groundwater management efforts across the country.
"We knew where the water was drawn from and where it was being applied, and we showed that the satellite data could tell us how much crop water use and pumping occurred for individual fields," explained Thomas Ott, assistant research scientist of hydrology at DRI and a lead author of the study. He added that detailed meter data is scarce, which has limited past research to broader regional assessments that couldn't focus on individual fields.
Evapotranspiration, which refers to the combined processes of water evaporating from Earth's surface and being transpired by plants, is a key factor in understanding water use. OpenET, which utilizes satellite data from NASA and the U.S. Geological Survey's Landsat missions, along with weather data such as humidity and temperature, helps estimate evapotranspiration rates across different landscapes.
The study examined two agricultural regions equipped with water flow meters: Diamond Valley, Nevada, and Harney Basin, Oregon. Both regions rely on groundwater for their expansive alfalfa and hay fields. In Diamond Valley, OpenET's estimates differed from meter readings by only 7%, while Harney Basin showed a 17% discrepancy, reflecting the different irrigation systems used in each area. Diamond Valley relies on center-pivot sprinklers, whereas Harney Basin uses a mix of flood irrigation and sprinklers.
"Our study shows that OpenET can really advance our understanding of agricultural water use, especially in basins without monitoring in place," Ott said. He noted that traditional methods rely on estimates of maximum water use, which don't account for varying conditions in a given year. By using satellite data, researchers can achieve a more accurate and realistic assessment of water use.
In fact, the study revealed that previous estimates of water use in Diamond Valley were much higher than the actual amount used, according to Sayantan "Monty" Majumdar, assistant research professor of hydrologic sciences and remote sensing at DRI and co-author of the study. By comparing groundwater pumping data with OpenET estimates, the researchers also determined that irrigation efficiency was high in both study areas, with 90% of water used by crops in Diamond Valley and 83% in Harney Basin.
The DRI team, including Ott and Majumdar, plans to continue this research as part of the Nevada Water Initiative. The project, in collaboration with the Nevada Division of Water Resources and the USGS Nevada Water Science Center, will extend their work to assess water use across the state. Nevada, the driest state in the U.S., relies on outdated water availability estimates, and this initiative aims to provide more up-to-date data to inform future water management efforts.
"The stakeholder engagement for this work is so important," Ott added. "Having grown up on a dairy farm myself, it was amazing to go into different parts of Nevada and see how the farmers work. One farmer graciously hosted me for a month while I was doing field surveys of meters and irrigation systems, and building those relationships is really important for our future work."
Research Report:Toward field-scale groundwater pumping and improved groundwater management using remote sensing and climate data
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