OpenET: Balancing Water Supply and Demand in the West – NASA

Monitoring Water Use and Drought with OpenET

At the end of 2022, 65 percent of the Western United States was in severe drought, the result of a two decades long mega drought in the Colorado River Basin that had captured headlines around the world.

However, it was flooding, not drought, that was making headlines when we began our research for this story about OpenET, a revolutionary new online platform geared towards helping farmers and water managers monitor and reduce water use in watersheds where supplies were not keeping up with demand.

Flooding in California

The start of 2023 brought flooding to many counties in California, leaving 68 percent of the state with suddenly little to no drought. And caused Forrest Melton, the NASA Project Scientist for OpenET and Associate Program Manager for agriculture and water resources with the NASA Earth Action program, to pause our video interview after a tree fell down outside his Bay Area home on a rainy day in March, 2023.

Coming online again after calling the fire department, Melton didn’t seem all too optimistic that the wet conditions would last. “California tends to swing between the two extremes of drought and flood,” Melton said. He referenced the 2016/17 winter which had particularly high precipitation but was followed by dry conditions during the following years, before the relief brought by the heavy rains, and flooding, in early 2023.

The Need for Better Water Management

According to NOAA’s National Integrated Drought Information System it will take more than one wet winter to replenish groundwater in many parts of the western United States. Groundwater levels across the California Central Valley and many parts of the Ogallala Aquifer continue to decline. The need for better water management remains essential, and yet the data necessary to support new approaches has not been broadly available.

The OpenET Project

Enter the OpenET project, a multi-disciplinary, collaborative effort to make satellite-based evapotranspiration (ET) data available to the public. Melton describes the project as providing invaluable and scientifically robust data at all scales, “that can be used to support day to day decision making and long range planning to try to solve some really long standing and important water management challenges in the West.”

Understanding Evapotranspiration

Evapotranspiration is the combined process of evaporation and transpiration, both of which transfer water from the land surface to the atmosphere as water vapor. Evaporation transforms water from the surface of the ground or bodies of water into water vapor, while transpiration is water vapor that is evaporated from plant tissues and escapes through the stomata, the tiny pores in plant leaves and stems. It is a process that is happening all around us almost all the time, but because water vapor is invisible to the human eye, it is very hard to measure on the ground.

The Role of Evapotranspiration in Water Management

To understand the effect evapotranspiration has on a local water cycle, picture a large decorative fountain. Typically, these fountains recycle the same water over and over. As a fountain runs, water is pumped out of the fountain heads, falls back into the fountain’s basin, and then flows back through the pipe system before starting the process all over again. We can think of the water remaining within this fountain’s local water system as non-consumptive water use. Some water, however, will be lost from the fountain’s local water system by evaporating from the pool’s surface or mist from the fountain’s spray.

Imagine the fountain also has lily pads growing in its basin. The lily pads will use the fountain’s water to survive and grow, losing some of that water to transpiration. The total water lost is evapotranspiration, and is considered consumptive water use, because it cannot be reused by the fountain. Tracking evapotranspiration can tell you how much water is removed or “depleted” from a local water system, and how much water needs to be added back in to support plant growth and maintain a healthy balance between water supply and water use. If too much water leaves the fountain, it will stop running. If too much water is added, it will overflow.

These concepts can be applied more broadly to the hydrologic cycle as a whole, and evapotranspiration data can play an important part in designing and implementing sustainable water management practices to combat larger issues like drought, as well as both short and long-term reductions in water availability.

The OpenET Platform

The OpenET team saw the important niche left open by traditional evapotranspiration measurement methods and filled it. They built upon decades of research funded by NASA, USDA and USGS and developed a new platform that can take easily accessible and already available data from satellite programs, like Landsat, and combine it with weather data to calculate the ET for every quarter acre of land. Satellites can record information like the Earth’s surface temperature and how much of the incoming light from the sun is being reflected back out to space. OpenET is able to use physically-based mathematical models to combine the satellite and weather data and output accurate data on evapotranspiration rates and volumes.

This information is then made easily accessible through OpenET’s Data Explorer, a free web-based tool that allows anyone with an internet connection to access the data OpenET provides. Users begin by selecting an area of interest from a map of the western United States that provides data at the satellite resolution of a quarter-acre, and also broken down into known areas of interest and individual agricultural fields, each color coded with a heat map of evapotranspiration. Cooler colors indicate higher rates of evapotranspiration while warmer colors indicate lower rates. Users can zoom into specific areas on the map, and with just a click, a chart pops up showing the evapotranspiration trends for a given area, for the current year and the past five years.

The chart can show monthly ET trends, useful for understanding seasonal fluctuations, and also cumulative trends, useful for understanding year-to-year changes in evapotranspiration. “The OpenET team took a user-driven design approach from the beginning, and each element of the Data Explorer and the open data services is there because a water manager or farmer asked for it,” Melton explained.

The OpenET Consortium

The OpenET consortium includes NASA, USGS, USDA Agricultural Research Service (ARS), Environmental Defense Fund (EDF), Google Earth Engine, California State University Monterey Bay (CSUMB), Desert Research Institute (DRI), Habitat Seven, Chapman University, Cornell University, University of Nebraska-Lincoln and close to a dozen other universities and experts across the U.S. NASA Ames Research Center and CSUMB have played key roles in the scientific and technical leadership of the effort from the outset, working closely with DRI, EDF and the recently formed non-profit OpenET, Inc. In addition, over 100 partners from the water management, agriculture and conservation community provided user requirements and assisted with the design and testing of the OpenET platform and tools.

Accuracy and Validation

Models like those built into OpenET can be extremely useful tools for understanding patterns in ET and water use, but are only helpful if their accuracy is known. The OpenET science team recently completed the largest accuracy assessment to date for field-scale satellite-based ET data, comparing the satellite data to ground-based measurements at more than 150 sites across the U.S. A key finding was that across all sites, an ensemble value computed from six different ET models performed the best overall, leveraging the strengths of each individual satellite-driven model. However, the study also found that some models performed best for particular crop types or regions, which is important information for water managers and farmers who need the most accurate data possible.

OpenET in the Sacramento-San Joaquin Delta

OpenET has already contributed to one significant win for farmers that affects how water use will be monitored and reported in the Sacramento-San Joaquin Delta. In 2023, the state began requiring farmers to maintain a water meter or measuring device on each diversion, where water is diverted from a river for irrigation. However, this measurement proved challenging and costly as there are thousands of diversions in the Delta, and the measuring equipment was inaccurate and difficult to maintain in this environment. After the launch of OpenET, farmers in the Delta worked with the Delta Watermaster, the California State Water Resources Control Board, the OpenET team and the Delta Measurement Consortium to develop an alternative compliance plan that used OpenET data to help streamline the water use required reporting for this complex region.

Expanding OpenET to Brazil

OpenET’s first international partnership is led by Anderson Ruhoff, a professor in Hydrology and Remote Sensing at the Federal University of Rio Grande do Sul, Brazil. Ruhoff learned about OpenET while he was in the US on a visiting professorship in Nebraska. He was intrigued and reached out to Melton who encouraged him to attend an upcoming conference in Reno, Nevada, where OpenET would be featured. In March, 2024, Ruhoff and OpenET launched an extension of the tool, called OpenET Brazil, with financial support from the Agência Nacional de Águas e Saneamento Básico (ANA), the Brazilian national water agency. The tool, called OpenET Brazil, will have similar goals as OpenET in the U.S., and the data collected will help improve Open ET’s accuracy overall.

The Importance of OpenET

Studying evapotranspiration can reveal the impacts of deforestation with even more clarity. And importantly, it’s also public information. “So not only the farmers and water managers but every citizen can check how much water is being used in their area, especially during drought. It’s democratic information in that way,” Ruhoff said. “I think it’s important to have this information openly available and to try and reach as many people as possible.” Melton feels there’s the potential to expand the project, if more people like Ruhoff are there to lead the way.

As water scarcity is increasingly becoming an urgent issue all around the world, it’s easy to imagine how many countries could benefit from OpenET data.

Written by Jane Berg and Rachel Sender, co-published with the Bay Area Environmental Research Institute

Program Contact:
Forrest Melton
NASA Ames Research Center
forrest.s.melton@nasa.gov

SDGs, Targets, and Indicators

1. Which SDGs are addressed or connected to the issues highlighted in the article?

• SDG 6: Clean Water and Sanitation
• SDG 13: Climate Action
• SDG 15: Life on Land

2. What specific targets under those SDGs can be identified based on the article’s content?

• SDG 6.4: By 2030, substantially increase water-use efficiency across all sectors and ensure sustainable withdrawals and supply of freshwater to address water scarcity.
• SDG 13.1: Strengthen resilience and adaptive capacity to climate-related hazards and natural disasters in all countries.
• SDG 15.1: By 2020, ensure the conservation, restoration, and sustainable use of terrestrial and inland freshwater ecosystems and their services.

3. Are there any indicators mentioned or implied in the article that can be used to measure progress towards the identified targets?

Yes, the article mentions the following indicators:

• Evapotranspiration data: The OpenET project provides satellite-based evapotranspiration (ET) data, which can be used to measure water-use efficiency and inform water management decisions.
• Accuracy assessment of ET models: The article mentions a study that assessed the accuracy of field-scale satellite-based ET data, which is important for ensuring the reliability of the data used for water management.
• Water use reporting: The article discusses how OpenET data is used for estimating water usage and streamlining water use reporting in the Sacramento-San Joaquin Delta, which can contribute to sustainable water withdrawals and supply.

SDGs, Targets, and Indicators Table

Source: nasa.gov