Lake Powell, the nation's second-largest reservoir and one that provides water and power to millions of people in southern California, has reached its lowest levels since its first filling in the 1960s.
Its companion reservoir, Lake Mead, is at levels almost as low.
Together, these reservoirs, fed by the mighty Colorado River, provide the water 40 million Americans depend on. Despite the storms that brought heavy rain and snow to California and other Western states in January, experts say it would take years of such weather to replenish the West's water resources.
“In the year 2000, the two reservoirs were 95% full. They’re roughly 25% full now,” said Brad Udall, a water and climate scientist at Colorado State University. "It’s hard to overstate how important the Colorado River is to the entire American southwest.”
What to know about the West's ongoing water crisis:
What is Lake Powell?
Lake Powell is the nation's second-largest reservoir. It was created by blocking the Colorado River at Glen Canyon in southern Utah and northern Arizona.
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It stores water as part of the Colorado River Compact and produces electricity through the hydroelectric turbines in Glen Canyon dam.
Work on the dam that created Lake Powell began in 1956 and was finished in 1966. It took 16 years for it to fill. At its highest, in 1983, the lake was 3,708 feet above sea level.
Today it stands at 3,522 feet.
What happens if the water level goes lower?
Lake Powell hasn't been this low since June of 1965, just two years after it began to fill with water.
The biggest worry: If the lake’s level falls much lower, it won’t be possible to get water out of it.
Why? Tubes that run water through hydroelectric turbines could soon be above the water. There are bypass tubes available below that point, but they weren’t designed for continuous use, so it’s not clear how they would fare.
Important quote: “If you can’t get water out of the dam, it means everyone downstream doesn’t get water,” said Udall. "That includes agriculture, cities like Los Angeles, San Diego and Phoenix."
Will water stop flowing? "That's a doomsday scenario," said Bill Hasencamp, Colorado River resources manager for the Metropolitan Water District of Southern California. Before things get to that point the Department of the Interior will require reductions in use.
How long until water stops flowing downstream? If the lake falls another 32 feet – about the amount it fell in the past year – power generation concerns become more urgent, Udall said. Snowmelt this spring is forecast to bring levels up somewhat.
Why is the water level so low?
The water in Lake Powell is low because the amount of water in the Colorado River has been falling for decades. At the same time, demand has risen due to increased population growth in the West.
Overall, the river's flow is down 20% in this century relative to the 20th century.
More than four scientific studies have pinned a large part of the decline on human climate change. It's partly that there's less rain and snow, partly that as temperatures rise, plants use more water and more water evaporates out of the soil which would otherwise have ended up in the river. In addition, the river itself experiences more evaporation.
"It’s unfortunate that the largely natural occurrence of a drought has coincided with this increasing warming due to greenhouse gases," said Flavio Lehner, a professor of atmospheric sciences at Cornell University. "That has brought everything to a head much earlier than people thought it would."
What about Lake Mead and the Hoover Dam?
Lake Mead is the nation's largest reservoir, a companion to Lake Powell. Mead was created when the Hoover Dam was completed in 1935. It supplies water and power to Arizona, California and Nevada.
Lake Mead's level is 1,047 feet above sea level. You would have to go back to April of 1937, also two years into its initial filling, to find levels that low. It is forecast to have a new record low next summer, said Hasencamp.
The lake isn't low enough yet to cause concerns about getting water out, but any hope of it refilling is years away, if ever, due to lowered rain and snow and increasing evaporation.
Some of America’s largest cities depend on the water from Lake Mead. “It’s 90% of the water supply to Las Vegas, 50% to Phoenix, effectively 100% to Tucson and 25% to Los Angeles,” said Udall.
What will happen if water levels keep dropping?
The Department of the Interior had asked the seven states of the Colorado River Compact to come up with a plan to cut between 2 and 4 million acre-feet of water by January. They weren’t able to come up with an agreement.
Because of that, it’s expected that the Department of the Interior's Bureau of Reclamation, which oversees water management, will mandate one sometime next year.
"This is apparently a decent (water) year, but still, if it turns dry again there are some pretty big reductions on tap and every state could be affected," said Hasencamp.
It will be painful but it doesn't mean the area can't thrive.
"The West might look different," said Hasencamp. "You might not see the lush lawns of today and endless fields of alfalfa, but you will see thriving communities and agricultural regions."
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This article originally appeared on USA TODAY: Lake Powell water level at historic low: Drought, water crisis in West