Ian James

The Desert Sun

The nation’s largest reservoir has broken a record, declining to the lowest level since it was filled in the 1930s.

Lake Mead reached the new all-time low on Wednesday night, slipping below a previous record set in June 2015.

The downward march of the reservoir near Las Vegas reflects enormous strains on the over-allocated Colorado River. Its flows have decreased during 16 years of drought, and climate change is adding to the stresses on the river.

As the levels of Lake Mead continue to fall, the odds are increasing for the federal government to declare a shortage in 2018, a step that would trigger cutbacks in the amounts flowing from the reservoir to Arizona and Nevada. With that threshold looming, political pressures are building for California, Arizona and Nevada to reach an agreement to share in the cutbacks in order to avert an even more severe shortage.

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“This problem is not going away and it is likely to get worse, perhaps far worse, as climate change unfolds,” said Brad Udall, a senior water and climate research scientist at Colorado State University. “Unprecedented high temperatures in the basin are causing the flow of the river to decline. The good news is that we have time and the smarts to manage this, if all the states work together.”

He said that will require “making intelligent but difficult changes to how we have managed the river in the past.”

As of Thursday afternoon, the lake’s level stood at an elevation of about 1,074.6 feet. The federal Bureau of Reclamation, which manages the reservoir and Hoover Dam, projects the level to decline a few feet more to an elevation of about 1,071 feet by the end of June, before the level begins to rise again with releases of water from Lake Powell.

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Under the federal guidelines that govern reservoir operations, the Interior Department would declare a shortage if Lake Mead’s level is projected to be below 1,075 feet as of the start of the following year. In its most recent projections, the Bureau of Reclamation calculated the odds of a shortage at 10 percent in 2017, while a higher likelihood – 59 percent – at the start of 2018.

But those estimates will likely change when the bureau releases a new study in August. Rose Davis, a public affairs officer for the Bureau of Reclamation, said if that study indicates the lake’s level is going to be below the threshold as of Dec. 31, a shortage would be declared for 2017.

That would lead to significant cutbacks for Arizona and Nevada. California, which holds the most privileged rights to water from the Colorado River, would not face reductions until the reservoir hits a lower trigger point.

READ MORE: Jewell sees progress in Colorado River talks

Representatives of California, Arizona and Nevada said last month that they hope to have a deal finalized by the end of the year for all three states to accept cutbacks earlier than otherwise required in order to head off a more serious crisis.

Interior Secretary Sally Jewell has said she is optimistic about the talks, calling the over-allocation of the river a shared problem that must be solved. During a May 4 visit to Southern California, she said that there has been “extraordinary collaboration” between the states in working toward a deal, and that the United States and Mexico have also been making progress in negotiations on a new accord to share water from the Colorado River.

While representatives of the three states have discussed the outlines of proposals to temporarily take less water from Lake Mead, they say considerable hurdles remain, including negotiations between water districts within each state.

The legal framework that divvies up the Colorado River was established during wetter times, starting with the 1922 Colorado River Compact. That and subsequent agreements have handed out more water than what flows in the river in an average year, leading to chronic overuse.

As population growth and heavy demand for water collide with hotter temperatures and reduced snowpack in the future, there will be an even greater mismatch between supply and demand, said Kelly Sanders, an assistant professor at the University of Southern California who specializes in water and energy issues.

“The question becomes how to resolve this mismatch across states that all depend on the river to support their economic growth,” Sanders said. She expects incentives and markets to help ease some of the strains on water supplies, “but it is going to be tricky to make the math work in the long term.”

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Government records show that the level of Lake Mead hasn’t been this low since 1937, when the reservoir was being filled.

Scientists have estimated that rising temperatures and the resulting declines in runoff across the Colorado River Basin could reduce the river’s flow by between 5 percent and 35 percent by the middle of the century.

“Human-caused climate warming will drive larger and larger flow reductions as long as emissions of greenhouse gases continue,” said Jonathan Overpeck, co-director of the University of Arizona's Institute of the Environment.

“The river is over-allocated even before climate change is factored in,” Overpeck said in an email. He said he thinks the negotiations will probably “focus on how to reduce the over-allocation, but will eventually have to focus on sharing the pain as climate change continues to reduce the flows.”

Ian James writes about water and the environment for The Desert Sun. Email: ian.james@desertsun.com Twitter: @TDSIanJames

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