Arizona water officials committed Thursday to reach a multi-state plan by the end of the year to stave off Colorado River water shortages, or at least lessen the impact.

The United States Bureau of Reclamation has been prodding Western states to wrap up drought contingency plans, one each in the lower and upper basins. Little snowpack, rising temperatures, and ongoing drought have led to steady declines in the river that serves 40 million people in seven US states.

The amount of water that gets sent to the lower basin states – Arizona, Nevada, and California – and Mexico depends on Lake Mead, the reservoir formed by Hoover Dam. No shortage has ever been declared, but the federal agency puts the possibility at more than 50 percent in 2020 and even higher in subsequent years.

Those states so far have avoided shortages through conservation, leaving water in Lake Mead and other efforts.

"The question is: How much of this do we need to do in the future and how can we stay out of shortage?" said Terry Fulp, director of the Bureau of Reclamation's Lower Colorado River Region. "The likelihood is that we probably can't."

The Arizona Department of Water Resources and the Central Arizona Project said they would form a committee to work out the details of a drought plan among Arizona water users and present it to the Legislature in January.

Ted Cooke, the general manager of the Central Arizona Project, said the key elements in Arizona are reaching agreement on how to handle any excess water, a program to allow tribes to store water behind Lake Mead, a mitigation plan for central Arizona farmers who would lose water under shortages, and a water conservation plan.

The drought contingency plan is meant as an overlay to 2007 guidelines on what levels would trigger shortages and where they would be felt. If approved, it would spread shortages more widely and loop in California. Mexico also has agreed to cutbacks.

The plan also gives states flexibility on how to help prop up Lake Mead and an opportunity to recover the water if the lake rises above certain levels. It's meant to last until 2026 when water users are scheduled to renegotiate the 2007 guidelines, but some provisions extend beyond that time.

"We can buy insurance now to provide more certainty for the coming years," said Reclamation Commissioner Brenda Burman, the keynote speaker Thursday. "It's Arizona's history that we face problems head on."

Right now, shortages begin when Lake Mead dips to 1,075 feet above sea level. Arizona is hit first and hardest as the junior user in the system.

Ms. Burman said other states would pressure her agency to limit Arizona's water deliveries if it doesn't agree on the drought plan. She also predicted lawsuits.

The federal agency has said it would rather the states negotiate a solution.

"That creates this real uncertainty," said John Fleck, director of the University of New Mexico's Water Resources Program. "No one knows exactly where and when they would step in and what that stepping in would look like."

American Indian tribes are expected to play a big role in the plan because they hold senior water rights and do not yet have the infrastructure to use their entire shares.

Gila River Indian Community Gov. Stephen Roe Lewis said the tribe is "fairly confident" a plan will be complete this year, given Reclamation's leadership and renewed cooperation between Arizona water officials.

Alan Dulaney, water policy administrator for the city of Peoria, wasn't so sure without more details.

"Various interests in Arizona are not all together on this," he said. "That will take some major persuasion."

Chris Harris, executive director of the Colorado River Board of California, said California agencies still are working out details of the drought contingency plan and keeping an eye on Arizona with "interest and cautious optimism."

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Southern Nevada water users should be able to absorb additional cuts outlined in the drought contingency plan and have an agreement to share costs, said John Entsminger, general manager of the Southern Nevada Water Authority in Las Vegas.

This story was reported by The Associated Press. Associated Press journalist Ken Ritter in Las Vegas contributed to this report.