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Proportionate limits may float Colorado River users through water crisis

If Colorado River stakeholders continue using water at current rates, researchers warn, water levels in lakes Mead and Powell may soon drop too low to produce hydropower. While the solution — use less water — is painfully obvious, how to actually implement changes across the seven states and Mexico which depend on the river remains a turbulent policy issue.

“We’re 23 years now into the manifestation of a really serious problem on the Colorado River that’s a combination of both overuse and climate-induced flow reductions,” said Brad Udall, senior water and climate research scientist at Colorado State University.

“Water is the one natural resource that really ties us all together, and you cannot make decisions about it as individuals,” Udall added.

After modeling 100 different scenarios, Udall and researchers at the University of Oxford and Utah State University published a paper in the journal Science on Thursday proposing proportionate restrictions on both the lower basin’s future growth and the upper basin’s current usage to stabilize the southwestern water supply.

The lower basin is made up of part of Arizona, Nevada and California; the upper basin includes Colorado, New Mexico, Utah, Wyoming and part of Arizona.

“The necessary reductions in water use must not be considered temporary either, but must remain in place until we either know the current drought has definitively ended and the reservoirs have recovered, or further consumptive-use reductions become required due to continued temperature increases,” explained Kevin Wheeler, a senior research fellow at the University of Oxford’s Environmental Change Institute in an email.

Without drastic action, the nation’s two largest water reservoirs, Lake Mead and Lake Powell are projected to decline from being 95% full in 2000 to 75% empty by the end of the year.

Forty million people living in the southwest U.S. and Mexico depend on the Colorado River, including those in Los Angeles, San Diego, Phoenix, Tucson, Las Vegas, Denver, Salt Lake City, Albuquerque and Tijuana. An additional 30 Native American tribes hold senior water rights as well.

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In addition to generating power for 2.5 million people, 70% of the river’s water nourishes 5.7 million acres of crops. Only 10% of the 1,400-mile river reaches Mexico, which also owns a stake in the water. Siphoned off across so many shareholders, the river rarely meets the ocean and a 2017 civil lawsuit attempting to grant the natural resource the rights of personhood dried up.

Several century-old agreements govern the law of the river, including the 1922 Colorado River Compact which doled out 17.5 million acre-feet of water each year to numerous stakeholders, an amount that even then “eschewed scientifically sound estimates that the available supply was potentially less.”

Additional modernisms unforeseen by the original compact negotiators further strain the river including climate change, drought, industrial agriculture and sprawling metropolitan development.

“There’s some really obscure and arcane aspects of the law of the river that I don’t think work in the 21st century, with climate change especially,” Udall said. “The Metropolitan Water District of Southern California supplies water for 20-plus million people, all of the LA basin plus San Diego, they’re actually junior relative to other Colorado River users in California and under the law, they get water last if there’s ever a shortage, and yet I don’t see how that you can make that work.”

While it never produced the promised 17.5 million acre-feet of water, the Colorado River supplied an average 15.2 million acre-feet per year through the 20th century, including 4 million to the upper basin and 9 million to the lower basin and Mexico.

As the river produces less water through the double-decade Millennium Drought, communities are pulling the difference from Powell and Mead. At the same time, the reservoirs have captured 20% less water than in pre-drought years.

“This should be a wake-up call to the fact that how things have been done in the past is not OK for the future or even the present moment anymore,” said Wheeler, lead author on the paper.  

By the U.S. Bureau of Reclamation’s calculations, Lake Powell now faces a 25% chance of being unable to produce hydropower in the coming years. Lake Mead faces a 40% chance of reaching the most severe management condition, triggering downstream reductions.

“If the Upper Basin commits to limit water uses to 4.5 million acre-feet per year (60% of their 7.5 MAF/year allocation, approximately 0.8 MAF/year higher than recent use), then the Lower Basin and Mexico must commit to more than doubling their current maximum reductions in existing use to 3.0 million acre-feet per year,” the paper explains. “In this scenario, the Lower Basin and Mexico receive 66.7% of their allocation, nearly matching the Upper Basin percentage.”

The near two-thirds split honors a part of the water pact allotting equal portions of water to the upper and lower basins, even as demand grew higher in actuality for the southern states compared to the northern.

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Meeting the challenge means reducing water use across the region for rural farmers and suburban landscapers alike, from cultivating drought-resistant plants to driving dirtier cars and even playing golf on drier turf.

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Felton Davis|CC BY 2.0

The bathtub ring around Lake Mead in 2021. Lake Mead faces a 40% chance of reaching the most severe management condition, triggering downstream reductions.