Next time you take a bite out of a juicy hamburger or chunk of cheese made in the western U.S., say thank you to the Colorado River.

Researchers released the most complete accounting so far of how the river’s water is used. They found that alfalfa — used as feed for beef and dairy cows — sucks up more water than all the cities and industries in the enormous Colorado River Basin.

The researchers incorporated new factors, like water used by nature, Mexico and out-of-basin water transfers, that haven’t been counted before. And with those numbers, the researchers made it clear that water use in the basin needs to drop by 22% to 29% to stabilize historically low reservoirs.

The research, published March 28, comes just in time: Seven state negotiators, 30 tribal nations and federal officials are all weighing how the river’s water will be managed for decades to come.

“Because of these intense negotiations going on over the future management of the Colorado River, we were quite anxious to get the most accurate numbers in front of those negotiators,” said Brian Richter, the study’s lead author and president of Sustainable Waters, a global organization focused on water scarcity challenges.

The U.S. Bureau of Reclamation, which owns and operates massive infrastructure in the Colorado River Basin, is the primary accountant of the river’s water. But past efforts to show how that water is used haven’t taken key factors into account, according to the study, published in the academic journal Communications Earth & Environment.

Reclamation incorporated water sucked up by plants and lost to the atmosphere, but only in riverfront ecosystems in the lower Colorado River. A 2012 report did not include the Gila River basin, which provides most of the water for the Phoenix area.

Other studies haven’t included water use in Mexico, tied to evaporation from reservoirs, or from transfers out of the basin to places including Denver, Fort Collins and Colorado Springs. Even a 2020 study led by Richter did not include all the relevant uses — and that has created uncertainty all around, Richter said.

The oft-cited study estimated that agriculture represented nearly 80% of the water used in the basin, but that study did not include usage by Mexico, the environment, exports out of the basin or through reservoir evaporation. When those uses are taken into account, agriculture represents half the overall use.

“We thought that it was about time for somebody to do an accounting for where all of the water goes,” Richter said. “We really wanted to bring nature into that conversation.”

Richter worked with 11 other researchers from universities around the country to compile what they say is the first complete accounting of water use in the Colorado River Basin.

Their research shows that the Colorado River was overused in 16 of the 21 years during the research period, 2000-2020. Water users overdrafted by 10% on average, driving down the basin’s biggest reservoirs, lakes Mead and Powell, which act like enormous water savings banks.

It may not be a surprise that irrigated agriculture uses the most water, taking up 52% of the water consumed across the 246,000-square-mile basin. But a shocking one-half of that is from just one crop used to feed livestock rather than humans: alfalfa.

Across the basin, alfalfa hay uses more than 5 million acre-feet of Colorado River water — that’s 26% of all the water consumed in the basin. One acre-foot roughly equals the annual water use of two or three households.

In the Upper Basin, irrigated agriculture consumes 2.8 million acre-feet, or nearly half the water used by Colorado, New Mexico, Utah, Wyoming, the environment, reservoirs and water exports out of the basin. Cattle-feed crops, like alfalfa, consume 90% of all water used by Upper Basin agriculture.

That means alfalfa uses more water than cities, commercial users and industries across the entire basin: Collectively, these users consume about 3.5 million acre-feet, or 18%, of the river’s water. The Colorado River provides water to 40 million people across seven Western states, 30 tribal nations and two states in Mexico.

Basinwide alfalfa production also uses more than the water sucked up by riparian ecosystems near rivers and wetlands, which use 19% of the river’s water.

Accounting for nature’s uses is one of the most helpful parts of the study, said Mehdi Nemati, assistant professor of environmental economics and policy at the University of California, Riverside.

“If there is a cutback, alfalfa and hay and pasture — those are the ones to go first. This is just purely looking at direct economic impacts,” said Nemati, who is working on an economic model to estimate the economic impacts of different policy decisions and climate scenarios.

Crops like alfalfa are relatively drought tolerant, always in demand and can be harvested by machine, a more affordable option than human labor. They also act like a buffer in dry years, when farmers can switch to other crops, Nemati said.

“If we don’t have that buffer then who has to go first, right?” he said.

All of these water users are facing a stress-filled future.

Natural and human consumption amounted to 19.3 million acre-feet on average between 2000 and 2019. Human uses, alone, equaled around 13.6 million acre-feet, according to the study.

The amount of water that is available for human use, in reality, looks more like 13 million acre-feet, Richter said. That gap grows when unused tribal water rights and additional needs are taken into consideration, he said.

The overstressed river basin is already feeling the impacts of climate change. For every 1.8 degree of warming in the Upper Basin, the basin loses 4% to 10% of its water supply, said Peter Goble, a climatologist with the Colorado Climate Center.

“When you consider that there is a very real possibility of warming an additional (3.6 degrees) over current levels, that’s looking at roughly a 10 to 20% reduction in streamflows,” Goble said. “Which is huge when you think about how we’re already dealing with shortages.”

Based on their comprehensive accounting, the researchers estimated that water users across the basin would need to cut their consumption by 2.4 million acre-feet to 3.4 million acre-feet each year to stabilize reservoir levels. Water users would need to cut an additional 811,000 to 2.4 million acre-feet per year between now and 2050 to account for climate impacts.

The cuts are roughly equal to a historic call in 2022 from the Bureau of Reclamation for states to reduce their use by 2 million acre-feet to 4 million acre-feet.

That means belt-tightening and economic impacts across the basin, Nemati said. Incorporating natural uses was one of the most helpful pieces of the new study. Next, he hopes researchers will model economic impacts based on these numbers — and that public policy will catch up to the data.

“It’s just overcommitted, and we’re not meeting our commitments,” Nemati said. “If we don’t know what is going to the environment, and we go into the negotiations in a year or so … then we can overcommit again. And in a couple of years, we’ll be in trouble again.”

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