By Robin Meadows
In 2015, when California was deep into a severe drought, state Senate Bill 88 tightened requirements for reporting water use. This posed a challenge for growers in the Sacramento-San Joaquin Delta’s 415,000 acres of farmland, where many irrigation systems are fed by siphons instead of pumps and so lack electricity to run water meters.
Alternative power sources proved troublesome. “I spent a lot of time on the side of levees replacing batteries and circuit boards, and fixing solar panels,” recalls Brett Baker, a water attorney with the Central Delta Water Agency who grew up on a Sutter Island pear orchard.
So when former Delta Watermaster Michael George suggested that Baker look into OpenET, a new online platform that uses satellites to track how much water plants consume, Baker was primed to make it work. That was in 2020. This year marked the launch of an OpenET-based website for reporting water use in the Delta, and 70 percent of growers there have already adopted it.
HOW SATELLITES DETECT CROP WATER USE
OpenET was developed to help people manage water sustainably. The platform gets data in part from Landsat satellites, which are managed by the National Aeronautics and Space Administration and the U.S. Geological Survey. Other inputs include surface weather such as air temperature, humidity, wind speed, and precipitation.
Landsat satellites have thermal sensors that detect heat on the Earth’s surface. In agricultural fields, the surface temperature reflects how much water is used by crops. This is due to a process called evaporative cooling, which uses heat from sunlight to evaporate water from, in this case, the leaves and tender stems of plants. In areas where plants use more water, the surface temperature is lower. The same process helps cool people down when they sweat.
Measuring crop water use is more important than ever. “With drought and climate change, we’re facing the ever increasing challenge of doing more with less and less water,” says Robyn Grimm, an Environmental Defense Fund hydrologist who is interim director of OpenET. Agriculture accounts for about 80 percent of the water used in California as well as in other western states.
TRACKING WATER USE IN THE DELTA
OpenET is well-suited to the Delta. The platform calculates how much water crops take up, formally called consumptive use, rather than how much growers divert as outlined in SB 88. OpenET may not meet that letter of the law but it does meet the intent in the Delta, where 55 islands are surrounded by a 1,100 mile network of rivers and sloughs, and the soil is extremely porous.
“The Delta has unique hydrology,” says Lindsay Kammeier, a State Water Resources Control Board engineer, explaining that any diverted water that is unused quickly returns to its point of origin. This means the two measures of water use—consumptive use and diversions—are much the same in the Delta.
Kammeier worked closely with water attorney Baker to help implement OpenET in the Delta. The result was a water use reporting website for growers called the Delta Alternative Compliance Plan (ACP). “It takes data directly from OpenET and sends it to the state Water Board,” says Baker. All growers have to do is input the boundaries of their fields, and Delta ACP does the rest. The website also lets growers double check their water use reports to ensure that they make sense.
“What I think is incredible with what happened in the Delta is that the state collaborated with growers on the ground,” Grimm says, adding that feedback from growers can help further finetune OpenET’s accuracy.
EASE OF USE, PRECISION AND TRANSPARENCY
Fourth generation Delta grower Jacyclyn Stokes is among the many early adopters of the OpenET-based Delta ACP. As a millennial who grew up in the digital age, she took on the task of reporting water use for her extended family. Collectively, the Stokes manage about 4,000 acres of wine grapes, walnuts and almonds near Lodi, a Central Valley town on the east edge of the Delta. This acreage is divided into several different water districts, each of which has its own reporting system.
Stokes vastly prefers Delta ACP for its ease of use. “We’re very busy during the growing season, and reading meters on irrigation systems is time-consuming,” Stokes says. “Delta ACP is much more user friendly.” Her fellow growers clearly agree: the Delta now has the highest rate of water reporting compliance in the state.
Delta Watermaster Jay Ziegler likes OpenET, which has a resolution of one quarter acre, for its precision. “It gives data on each diversion that is localized in time and space, and helps us understand the Delta water budget,” says Ziegler, who is former policy director of The Nature Conservancy, which co-sponsored SB 88. “It gives us a much finer picture of water use than in any other part of the state.” A water budget accounts for flows into and out of a region.
The platform’s transparency is another advantage. Nearly all aspects of OpenET are publicly available, from the raw data to most of the models that estimate crop water use. Trust in the process is key to agreeing on a data set for how much water is used, and working from the same data is key to managing water use. “Open ET helps us get to one data set,” Ziegler says.
Brent Vanderburgh, a state Water Board geologist, puts it this way: “OpenET provides a consistent reference that could help make water management decisions where there are competing consumptive use data sets, or help to limit the effect of combat science.”
BEYOND THE DELTA
Delta ACP is the state Water Board’s first regulatory application of OpenET and, Vanderburgh says, the platform “is likely to become a tool used in most parts of the state and throughout the west.” The platform currently covers 17 western states and plans to expand into the eastern U.S. too.
Other possible applications of OpenET include the Sustainable Groundwater Management Act, which requires Groundwater Sustainability Agencies in 140 basins to halt overdraft and bring levels of pumping and recharge into balance by 2042. These agencies also must report progress toward these goals.
“To do this, they need a complete picture of the fate of water,” Grimm says. Rain, snowmelt, and irrigation water applied to crops can take various pathways, from recharging groundwater to running off into waterways to being consumed by plants; the latter is where OpenET comes in.
OpenET could similarly track the fate of water in mountains, where thirsty forests can drink a lot of the snowmelt Californians depend on for water during the summer. Knowing how much snowmelt goes to forests and how much makes it into streams is critical to forecasting water supplies for people and aquatic ecosystems.
The platform could also shed light on whether forest thinning would actually boost the water available for use. Questions include whether this strategy increases runoff, and how much water forests use as they grow back.
Water attorney Baker hopes OpenET will usher in a new era of water management. “It’s a very important tool in the toolbox and may even be a new box itself,” he says. “I’m hoping we can make more informed decisions, based on more accurate and more relevant data, and elicit better outcomes for water users and the environment.”
