Drought is a significant issue in the Western United States, prompting water managers in the area to create plans aimed at conserving groundwater, a vital resource. Groundwater is typically pumped to irrigate crops, and historically, flow meters have provided the best insight into groundwater usage. However, these meters are not common, leading scientists to explore whether OpenET—a platform utilizing satellite imagery to measure evapotranspiration—could address this lack of data.
Drought is a significant issue in the Western United States, prompting water managers in the area to create plans aimed at conserving groundwater, a vital resource. Groundwater is typically pumped to irrigate crops, and historically, flow meters have provided the best insight into groundwater usage. However, these meters are not common, leading DRI scientists to explore whether OpenET—a platform utilizing satellite imagery to measure evapotranspiration—could address this lack of data.
A new study published on August 8 in a special issue of Agricultural Water Management analyzed data from groundwater meters alongside OpenET estimates for agricultural fields in Nevada and Oregon. The findings indicate that OpenET is capable of accurately estimating groundwater usage for crop irrigation on an individual field basis. This research is the first to trace water from a groundwater source directly to a specific crop field, evaluating how much water the crops consumed and providing insights into how efficiently irrigation systems function. The method could be valuable for water management strategies nationwide.
Thomas Ott, an assistant research scientist in hydrology at DRI and lead author of the study, stated, “We knew where the water was drawn from and where it was applied, and we demonstrated that the satellite data could inform us about the crop water use and pumping for specific fields.” He noted that access to detailed meter data is infrequent, which has led previous research to focus on broader areas rather than individual fields.
Evapotranspiration is the process in which water is returned to the atmosphere through evaporation and plant transpiration. OpenET combines data from NASA and U.S. Geological Survey Landsat satellites with weather factors like humidity, air temperature, and solar radiation to estimate evapotranspiration across various landscapes globally.
This study focused on two agricultural areas—Diamond Valley in Nevada and Harney Basin in Oregon—that have irrigation water flow meters allowing for comparison with OpenET data. Both regions are heavily reliant on groundwater and cultivate thousands of acres of alfalfa and hay. The study found that there was a 7% variation between the metered data and OpenET estimates in Diamond Valley, while Harney Basin showed a larger discrepancy of 17%. The researchers aimed to evaluate OpenET’s performance across different irrigation methods: Diamond Valley predominantly uses center-pivot sprinklers while Harney Basin employs a combination of flood and sprinkler irrigation.
Ott remarked, “Our study illustrates that OpenET can greatly enhance our understanding of agricultural water usage, particularly in areas lacking proper monitoring.” He explained that traditional approaches often use an estimate of the maximum water usage for a typical healthy crop field in an average year, but many variables can lower that figure. Using satellite data offers a more realistic assessment.
By analyzing both metered data and OpenET estimates, the study revealed that the assumed water usage figures in Diamond Valley were significantly higher than the actual amounts used, according to Sayantan “Monty” Majumdar, an assistant research professor at DRI and co-lead on the study. Furthermore, the data indicated that irrigation practices in both regions were highly efficient, with 90% of irrigation water being utilized by crops in Diamond Valley, compared to 83% in Harney Basin.
Ott, Majumdar, and the DRI OpenET team aim to broaden this research to assess agricultural water usage across Nevada as part of the Nevada Water Initiative. As the driest state in the U.S., Nevada often depends on outdated estimates regarding water availability and utilization. The initiative will leverage advances in research techniques and technologies to provide a more accurate evaluation for future water management. This project involves collaboration between DRI, the Nevada Division of Water Resources, and the USGS Nevada Water Science Center, along with agricultural stakeholders statewide.
Ott emphasized the importance of engaging stakeholders throughout this research. “Having grown up on a dairy farm myself, it was incredible to visit various parts of Nevada and witness farmers in action. One farmer kindly hosted me for a month while I conducted field studies on meters and irrigation practices, and establishing those relationships is crucial for our ongoing work,” he noted.
