Accelerating data-driven water management in the West

Google Earth
Google Earth and Earth Engine
5 min readOct 21, 2021


Editor’s note: Today’s post is by Robyn Grimm (Environmental Defense Fund), Forrest Melton (NASA / CSU Monterey Bay), Justin Huntington (Desert Research Institute), and Tyler Erickson (Google), a few of the organizations collaborating on the OpenET project.

Every day thousands of people across the western United States make decisions about water — farmers, water managers, and state and federal planners. And yet, they are often looking at incomplete data on water consumption, even as drought and extreme heat put more pressure on increasingly scarce water supplies for communities, wildlife, and agriculture.

A collaboration of more than a dozen organizations has come together to fill this major information gap in water management through a new online water data platform called OpenET. OpenET uses Google Earth Engine to analyze publicly available Earth observations and generate water use data that is critical for enabling more sustainable, data-driven water management.

What is ET?

The “ET” in OpenET stands for evapotranspiration, which is the process by which water evaporates from the land surface and transpires from plants. Because water transferred from the land to the atmosphere through ET is unavailable for other uses in a local watershed, it is often referred to as “consumptive use” of water.

For irrigated agriculture, satellite-based estimates of ET provide a measure of the water used to grow our food — the biggest share of water consumption in most arid environments around the world. Managing water without ET data is like managing a household budget without knowing how much money you are spending day to day.

In this blog, we’ll describe how ET data has been used at field and regional scales. But first, a little more on how OpenET works.

Harnessing the power of Earth Engine for collaborative science

OpenET uses observations from Landsat, other satellites, and weather data to estimate ET. As anyone who has run through a sprinkler on a summer day knows, evaporation cools down surfaces. This cooling effect is visible to Landsat’s thermal sensor, which “sees” the effect of ET as lower land surface temperatures. Cooler temperatures mean more water is being used (transpired) by plants and evaporated from the land surface.

While models for calculating ET from satellite imagery have been developed by several universities and research groups over the last several decades, they require multiple inputs — such as satellite observations, weather models, land cover, and topography — and are computationally intensive to run. Earth Engine is making it possible for the first time to run several ET models using Landsat and gridded weather data over millions of square miles, ultimately enabling OpenET to provide daily, monthly, and annual ET data for most agricultural fields across the 17 western states.

Of course, data is only valuable to the degree that it’s trusted. Earth Engine has also made it possible for leading researchers across the globe to work together on the OpenET platform to collaboratively test and improve their models to generate the best possible ET data.

Enabling new water management solutions

Meeting the challenges of a changing climate requires innovative, locally driven solutions, including water conservation, trading, and other programs that help protect the financial viability of farms and communities when water is scarce.

In California, for instance, Rosedale-Rio Bravo Water Storage District is using OpenET data in a groundwater accounting and trading platform that it developed to comply with the state’s Sustainable Groundwater Management Act. The law requires the region to balance groundwater supply and demand by 2040.

Data from OpenET lets landowners track their annual water budget by parcel to inform irrigation and crop management, and helps Rosedale track the water budget for the entire district. The platform also will enable the district to launch a water trading platform to give farmers more flexibility in managing their water.

OpenET also can be incredibly powerful in helping to develop water conservation programs by enabling landowners to quickly assess year-over-year water savings from conservation efforts, like reduced irrigation or crop switching, and compare those results against changes in yield and revenue. This helps communities design local solutions to meet their water conservation goals that also maintain agricultural production and preserve rural economies.

Reducing wildfire risk while protecting watershed health

In addition to contributing to more acute droughts, climate change is leading to more intense wildfires, which also jeopardize water supplies. Salt River Project (SRP), one of the largest water and power utilities in Arizona, knows about this connection firsthand from operating a system of reservoirs that rely on healthy watersheds and forests.

In recent decades, these forests have been impacted by large wildfires, which threaten water quality and reliability, infrastructure, human health, and wildlife. SRP staff is using OpenET data to improve their understanding, at large scales and low cost, of the impacts of forest restoration on watershed hydrology.

Data for a future with less water

Finally, OpenET is a valuable tool to help farmers improve irrigation — a critical piece of their operations under greater pressure as a result of climate change and drought.

Daily ET data, which OpenET will soon make available, can help irrigators reduce applied water by up to 40% while sustaining crop yields and quality, according to ongoing trials by NASA and the University of California Agriculture and Natural Resources Institute. ET data also can help improve estimates of groundwater recharge during wet years, when irrigating in excess of ET can replenish groundwater. For some growers, OpenET may also help them identify periods of unintentional crop water stress, allowing them to increase yields by applying additional irrigation.

Mark Owens is an Oregon farmer and state representative who has been at the forefront of using ET data where he lives in the Harney Basin, which is experiencing a groundwater deficit of at least 120,000 acre-feet per year. (One acre-foot equals 326,000 gallons.)

“We’ve used ET data to gain a better understanding of our water consumption and design more efficient irrigation systems that use about 25% less applied water,” says Owens. “This could translate to a savings of 18% to 20% on electricity costs for pumping, too.”

After seeing such positive results, Owens introduced legislation to enable Oregon water agencies to use OpenET to create water budgets for every groundwater basin in the state.

“If you haven’t experienced climate change yet, it’s coming,” Owens says. “Farmers and water managers in the West need data and technology like OpenET to help us adapt.”

Mark Owens looks at his cellphone for ET data, which he has used to improve irrigation management on his alfalfa fields in Oregon.

OpenET has been developed by NASA, Desert Research Institute, Environmental Defense Fund, Google, U.S. Geological Survey, U.S. Department of Agriculture, University of Nebraska-Lincoln, University of Idaho, University of Maryland, and University of Wisconsin-Madison. Learn more about how other partners use OpenET.