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This stunning timelapse shows the megadrought’s toll on the West’s largest reservoir

Vox.com logo Vox.com 4/21/2021 Lili Pike
a group of people on a beach near a body of water: Lake Mead marina, south of Las Vegas, Nevada, on August 23, 2020. © Daniel Slim/AFP via Getty Images Lake Mead marina, south of Las Vegas, Nevada, on August 23, 2020.

Just how bad is the drought in the Western US? The shrinking of Lake Mead, the country’s largest reservoir, is a troubling indicator.

The massive man-made lake, which straddles the border of Arizona and Nevada, is now only at 39 percent of its full capacity, down from 44 percent in April 2020. The lake’s water level has dropped over 10 feet since last April, according to the latest data from the Bureau of Reclamation. Which means mandatory restrictions on the amount of water surrounding states draw from Lake Mead could be triggered in the next few months.

“This year will be really telling because it will provide a stress test of the newest policies that we thought were stricter but likely will need to be even more strict in the future,” said Elizabeth Koebele, a political scientist at the University of Nevada who focuses on water policy.

The impending restrictions have been a long time coming — the reservoir started contracting well before 2020, as Vox writer Brad Plumer explained in 2016. The latest drought in the West is but one episode in a two-decade megadrought, and it has taken a toll on the Colorado River, which feeds Lake Mead.

The animated map below, from Google Earth’s new Timelapse feature, shows just how much the reservoir’s boundaries have shriveled since 1985.

Lake Mead’s dropping water levels will affect Arizona’s water supply as soon as next year

Lake Mead’s recent contractions are concerning because the body supplies water to 25 million people across Arizona, Nevada, California, and Mexico. Built in 1936, the Hoover Dam and the attached reservoir have shaped the geography of the West, making life in Las Vegas and Los Angeles possible.

As the lake level has dropped, states have so far managed to avoid reaching the point where mandatory water restrictions kick in, but it looks like they are coming soon.

The Bureau of Reclamation keeps tabs on the lake by measuring its height at Hoover Dam. There, the water level is currently at 1,081 feet, and the Bureau projects it will drop below 1,075 feet as soon as June. After it crosses that threshold, the federal government will declare an official water shortage. Under a Drought Contingency Plan agreed upon by the affected states in 2019, some states will start to see big cuts in how much water they receive from Lake Mead starting in 2022.

Based on the pecking order from past negotiations, Arizona will have the biggest reductions in allocation from Lake Mead while California won’t face restrictions until the reservoir drops below 1,045 feet. The agreement dictates that Arizona will have one-third of its water supply from the reservoir cut, Ian James reported for AZ Central. Farmers will be among the most impacted, according to the state’s drought plan, but they will be allowed to use groundwater resources to compensate to some extent.

As a result of the preemptive drought planning, states have already prepared for the inevitable point when they will have to endure such cuts, said Koebele. “The basin has become increasingly collaborative over time, and people are thinking about it as, ‘It’s not if this happens, it’s when it happens and how do we best handle it.’”

Generally speaking, she said, cities will be relatively unaffected by any cuts for now, whereas farms, which consume the vast majority of the basin’s water, will have to start investing in technologies like drip irrigation to become more efficient.

Climate change poses a serious long-term threat to the millions who depend on the Colorado River

The imminent resource crunch is just the beginning of the problems for the millions of people in Arizona, Nevada, California, and Mexico who depend on Lake Mead and the Colorado River for their water.

Rising global temperatures are expected to bring more frequent and more intense droughts to the Southwest, according to the latest National Climate Assessment, which was authored by 13 US federal agencies in 2018. Climate change is also increasing the likelihood of long-term megadroughts like the one we are seeing now.

In a 2020 study published in Science, US Geological Survey researchers found that warming will reduce the flow of the upper Colorado River by 14 to 26 percent by mid-century under a moderate climate action scenario.

“Climate change is really severely impacting the basin,” said Koebele. Rising heat increases evaporation, she explained, “Even when we get a good snowpack, if the soil is super dry we can see really big reductions in run-off.” That means less precipitation from the mountains ultimately makes it to the river.

To adjust to an increasingly water-scarce future, basin states and stakeholders are starting to negotiate a post-2026 deal, which will set the framework for the coming decades. In the meantime, cities and farms will need to continue to find ways to make their water use more efficient. Arizona is even considering building a desalination plant with Mexico to import water from the sea.

“We are going to hit a peak with efficiency and conservation, or hit a limit eventually, but there is still more to do there,” Koebele said.

As for the coming year after Lake Mead drops below 1,075 feet, it will be the first stress test for states as they collaborate to conserve Lake Mead’s water for the future.

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