What could cuts in the dwindling Colorado River mean for states?

washington • The Biden administration this week unveiled two ideas to reduce water use from the dwindling Colorado River, which serves 40 million people.

The 1,450-mile river is a lifeline for seven U.S. states, dozens of Native American tribes and two states in Mexico. It irrigates nearly 5.5 million acres of farmland in the US and Mexico and generates hydroelectric power that is used throughout the West.

In recent decades, drought, climate change and an imbalance between the river’s flow and the promised amount of water have forced federal officials to consider new moves.

[Read more: Biden admin analysis on Colorado River puts pressure on Lower Basin states for cuts]

Tuesday’s Interior Department analysis is considering two ways to force cuts in water supplies for Arizona, Nevada and California: Use the existing water priority system or use the same percentage across the board. California and some tribes with elder rights to water benefit more from the first option. Arizona and Nevada, mostly with junior rights, don’t feel as much pain under second.

Federal officials have not taken a position.

What prompted the analysis?

The US Bureau of Reclamation, which reports to the Department of the Interior, made a bombshell announcement last June as water levels in major Colorado River reservoirs fell to historic lows. Federal officials said pool water use needs to be reduced by 15% to 30%.

States struggled to find consensus, tensions mounted, and ultimately no agreement was reached. But challenges on the river remained, and federal officials said they must consider changing operations at Hoover Dam, which holds back Lake Mead, and Glen Canyon Dam, which controls Lake Powell. The reservoirs on the Colorado River are the largest built in the United States

The states regrouped and developed competing ideas to reduce consumption in January. California proposed a plan separate from the other six states – Arizona, Nevada, New Mexico, Colorado, Wyoming and Utah.

Proposals released Tuesday built on some of those ideas and rejected others.

How would each plan affect California?

California is entitled to 4.4 million acres of water per year, more than any other single state in the Colorado River basin. California’s rights are also among the safest.

Water portions for California, Arizona, Nevada and Mexico are from Lake Mead.

Under current rules, California won’t lose water until Lake Mead falls below 1,045 feet — about a foot lower than it is now. Even in the worst-case scenario, California would fare better than its Lower Basin neighbors.

The priority-based proposal would benefit California cities and farming districts such as the Imperial Valley. It is a vast agricultural region in the southeastern state that grows a significant amount of the country’s winter vegetables. The valley would not lose additional water under this proposal due to its senior citizen rights.

California fares far worse if the cuts are more evenly distributed. As Lake Mead dips deeper, it would need to cut more water, eventually up to about a fifth of its allotment.

Agricultural regions would be severely affected, likely meaning growers would leave some fields unplanted. Cities like Los Angeles and San Diego have other water sources, but a loss of river water could result in conservation regulations restricting activities like watering grass.

What about Arizona?

Arizona is in a tough spot whichever proposal goes ahead, as much of its water has subordinate status in the priority system.

The state’s water users are entitled to 2.8 million acre feet of Colorado River water annually. Native American tribes along the Colorado River and farmers near Yuma in southwestern Arizona take precedence over cities.

The Central Arizona Project, which manages a canal system that supplies water to metropolitan Phoenix and Tucson, monitors about 1.6 million of those acres. It has already endured two rounds of mandatory cuts and would be hit hard under the priority-based proposal.

If the cuts are distributed based on the priority system, Arizona risks losing nearly two-thirds of all its river water by 2024. Under the proportional system, which requires California to contribute more, Arizona would lose about a third.

Under either option, some Arizona water users could cut their allocations to zero if Lake Mead falls deep enough to risk hydroelectric production.

It’s not clear how both plans would affect farmers and cities. The Colorado River isn’t the only source of water for Arizona’s most populated areas. Many have been damming water underground for years.

What about Nevada?

Nevada has the smallest amount of the Colorado River in the Lower Basin, 300,000 acre feet, which supplies metropolitan Las Vegas.

Water recycling and other measures in southern Nevada have secured the water supply. The state does not use its full allocation. There would be some relatively minor cuts, but it’s unclear how deeper cuts would affect residents.

What about the upper pool?

Neither plan would affect water supplies to Colorado, Utah, New Mexico or Wyoming.

The four states get water directly from the river and most years do not use the full 7.5 million acres allocated to the Upper Basin.

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Why is the analysis important?

The analysis provides water users with new starting points for negotiations on reductions.

“The question will be how bad is this pain and who is it affecting,” said Jay Weiner, an attorney for the Quechan Indian tribe of Fort Yuma.

The tribe along the Arizona-California border has senior rights to water and opposes bypassing the priority system, as does California and its irrigation districts.

Bill Hasencamp, Colorado River resources manager for Southern California’s Metropolitan Water District, says the two proposals will spur renewed efforts to reach consensus over the next 45 days. That goal was elusive for almost a year.

Would doing nothing risk disaster?

Yes.

Doing nothing increases the risk that Lake Powell and Lake Mead will sink so low that the hydropower of their levees will be threatened. Power generation has already been impacted by low lake levels. Volunteer to save water can help. Precipitation, runoff from the Rocky Mountains, and temperature also play a role.

The priority-based proposal would protect Lake Powell water levels – but could result in reduced capacity at Hoover Dam. Sharing the percentage cuts would help stabilize power generation at both dams.

Everyone agrees that relying on the existing rules and guidelines, which expire in 2026, is not really an option.

What happens next?

States, tribes and other water users have until May 30 to comment. Federal officials are expected to announce a formal decision this summer. If states and tribes fail to reach consensus, that deadline could be delayed.

Meanwhile, in the coming weeks and months, US and Mexican officials will meet to discuss Mexico’s role. The treaties governing Mexico’s voluntary water conservation are independent of any agreements made between US states and Native American tribes.

Federal officials will announce how much water is available for 2024 in mid-August, along with any reductions in lower basin states and Mexico.

The Associated Press receives support from the Walton Family Foundation for reporting on water and environmental policies. The AP is solely responsible for all content.