New satellite technology could be a critical part of the future of water trade in the San Joaquin Valley, according to those working on the technology. OpenET, an online platform that uses satellite imagery to estimate the amount of water used by different crops, was publicly launched on October 21.
The platform is already tested in the San Joaquin Valley. And in January, the state will allow property owners in the Sacramento-San Joaquin Delta to use OpenET data instead of measuring their water usage.
“In California, we still have a long way to go in many places to enable water exchange programs,” said Christina Babbitt, director of climate resilient water supply systems for the Environmental Defense Fund. non-profit. “One of the biggest needs is to have consistent data that can be used to inform management actions across these very local borders if we are to enable things like water trade. “
How the technology works
OpenET uses satellite imagery to calculate evapotranspiration, when water evaporates from the surface of the Earth and plants.
“The basic physical principles used to calculate satellite evapotranspiration are familiar to anyone who has walked through a sprinkler on a hot summer day,” wrote Robyn Grimm, project manager on OpenET and director of resilient water systems at climat for EDF, in an e-mail. “After passing through a sprinkler, the water evaporates and cools your skin. This same process occurs on the surface of the Earth.
This cooling effect is visible to satellites and can be used to calculate the water consumption of plants. Cooler temperatures mean more water is used.
The platform has been in development for four years. It is a combined effort that includes entities such as NASA, EDF, United States Geological Survey, SD Bechtel, Jr. Foundation, several universities, and more. The platform targets the western United States and other parts of the world.
Potential benefits for the valley
OpenET could be of use to the San Joaquin Valley, in particular, in several ways, Grimm wrote.
The data can help inform irrigation management and water scheduling to save water and reduce costs, Grimm wrote. It can also help water managers, landowners and communities develop more accurate water budgets, conservation programs and, of course, business platforms, Grimm added.
The data could also potentially be used to inform groundwater pumping restrictions as the state begins to reduce pumping in hopes of sustaining its over-pumped aquifers.
The Rosedale-Rio Bravo water storage district in Kern County already uses OpenET. The district uses the platform so that landowners can track their own water budgets per plot. Rosedale also experimented with an online water market simulation.
“We do our homework and compare it to what’s out there,” wrote Markus Nygren, technical engineer at Rosedale on OpenET, in an email. “But we are not 100% convinced on this. “
Some districts are already using satellite data
OpenET is not the only platform available to estimate evapotranspiration. Land IQ provides a similar service and is used by several River Basin Districts in the San Joaquin Valley including the Laguna Irrigation District in Kings County and the Semitropic Water Storage District in Kern County.
Relying on the platform alone is not enough, said Jason Gianquinto, CEO of Semitropic. Semitropic started using satellite data in 2016, but did not become fully online with the platform until 2018. The Land IQ system is combined with ground base station information collected from across the district for a maximum precision.
The system is working well, said Gianquinto. But it took a while to get there and was far from perfect at the start.
As for OpenET, Gianquinto believes it could be useful on a large scale, for example to understand trends over large areas.
“But if you want to explore a specific plot or field, I think that’s a gap in OpenET,” Gianquinto said. “You just have to understand the limitations of the dataset and I think that’s where I’m concerned. “
Accuracy and margin of error
OpenET has published information on the accuracy of its data. Its data was compared at nearly 150 ground-based measuring stations across the United States.
At sites measured during the growing season, there were very few errors. But at sites measured during monthly and daily periods, some average error rates increased slightly above OpenET targets.
What is considered a good margin of error for this type of technology? There is no right answer to this question, according to Josue Medellin-Azuara, associate professor of civil and environmental engineering at the University of California at Merced.
“It would really depend on the application,” Medellin-Azuara said. Even small percentages of error can amount to significant amounts of water in some areas, he said. “It’s real water for a lot of people.”
Still, the platform is a big step forward for water management, Medellin-Azuara said. And the accuracy of OpenET will only improve over time, as it incorporates more verification and partnerships in the field, he added.
“These types of approaches improve transparency,” Medellin-Azuara said. “They help with water management, research, a lot of other things to improve water use in California.”
About SJV Eau
SJV Water is an independent, non-profit news site dedicated to water coverage in the San Joaquin Valley.