Lake Mead, the enormous reservoir of Colorado River water that hydrates Arizona, Nevada, California and northern Mexico, is receding to a level not seen since it was first being filled in the 1930s, stoking existential fears about water supply in the parched Southwest.
Heightening those concerns are recent signs that the region's record-breaking, 11-year drought could wear on for another year or longer. July not only saw the lake drop to 1956 levels but also brought cooling temperatures in the Pacific Ocean that signaled a developing La Niña system, historically a harbinger of more hot and dry weather.
The La Niña "appears to be strong, and it might even last two years," said Brad Udall, director of the National Oceanic and Atmospheric Administration's Western Water Assessment program at the University of Colorado.
In the 75 years since the workers began to hold back the Colorado River behind the Hoover Dam, the lake's water has taken two precipitous plunges: first during the prolonged drought of the 1950s, which ranks second only to the current dry spell, and again in the mid-1960s, when water managers began filling Mead's cousin 250 miles upstream, Lake Powell.
Neither dip was as severe or prolonged as that of the past decade. Nearly full in 1999, Mead has shrunken to 40 percent capacity, causing the ominous, bleach-white bathtub ring on the surrounding mountainsides to grow taller by the year. In the past five months, the lake steadily shed another 15 feet, to about 1,087 feet above sea level today. Four more feet and the lake surface will hit what would be the lowest mark since 1937 -- something the government projects will happen in October.
"It's a clear warning," said Tim Barnett, a scientist and Lake Mead expert at the Scripps Institution of Oceanography who sounded the alarm in 2008 with the prediction that Mead had a 50 percent chance of running dry by 2021.
"This is what basically the models are telling us should be happening and, by golly, there it is, right there in front of you," Barnett said. "The thing that's astounding to me is the head-in-the-sand attitude of the bureaucrats that we've talked to."
Federal water managers have the option, under certain conditions, to boost Mead's supplies by releasing water from Lake Powell -- an option that they may be forced to exercise but that amounts to little more than the water management equivalent of Whac-A-Mole.
"That's a temporary fix," Barnett said. "Over the long haul, they're in trouble."
Mead's disappearing act highlights the Southwest's chronic overuse of Colorado River water. Trouble originated with the 1922 Colorado River Compact, which estimated the river's water flow at 16.4 million acre-feet per year and divided that up among seven states and Mexico. Today, scientists believe the compact overestimated the flow by as much as 2 million to 3 million acre-feet, because flow measurements taken during the 20th century were skewed -- it was the wettest century of the last 500 to 1,200 years, according to recent paleoclimate studies of tree rings.
Climate change threatens to stretch the river's water even further. Over the last decade, the Southwest has suffered the sharpest temperature increase on the continent, declining late-season snowpack, loss of vegetation and rampant wildfires -- all while growing faster than any other region in the United States. Eight studies completed from 1991 to 2007 predict that climate change will reduce the snowpack runoff that feeds the Colorado River anywhere from 6 percent to 45 percent over the next half-century.
The bottom line is that Mead has consistently had more water withdrawn than deposited, resulting in an average annual deficit of 1.6 million acre-feet -- a gap that will only expand as temperatures rise.
"We need to be making major policy changes to Western water," Udall said. "And a lot of people aren't willing to do it until you have a full-fledged crisis on your hands."
Federal officials attempted to address the problem in 2007, striking a landmark "shortage sharing" agreement with Western states that dictates increasing cutbacks to Mead's water deliveries as the surface drops. Other efforts are under way, including creative water conservation programs like "Cash for Grass" in Las Vegas, which pays homeowners $1-per-square-foot to convert to desert landscaping. The feds are also building new reservoirs, such as the relatively tiny, soon-to-be-completed Drop 2 Storage Reservoir, built to catch and save excess water sent downstream from Mead that would otherwise flow into Mexico, unused by the United States.
"There's a bit of a perception that folks aren't doing anything about it," said Terry Fulp, deputy regional director of the Lower Colorado Region for the Bureau of Reclamation, the federal agency that operates Lake Mead, Lake Powell and the Hoover Dam. "As we entered this current drought at the start of this decade, it became very apparent we needed at least to sit down and talk about how we are operating the reservoirs and also put some proactive measures in place."
Nonetheless, scientists contend that the cutbacks called for in the 2007 agreement, euphemized by then-Interior Secretary Dirk Kempthorne as an "agreement to share adversity," are not enough to stop the hemorrhaging.
The lowest reduction mandated by the agreement would cut deliveries by 333,000 acre-feet, about half of what Los Angeles consumes in a year, should the lake's surface fall another 12 feet to 1,075 feet above sea level, or about 33 percent capacity. "Many people think that could happen as early as next year," Udall said.
Greater cutbacks and impacts follow as Mead's surface plunges further. When the 28.5-million-acre-foot reservoir's surface hits 1,050 feet, or about 26 percent capacity, deliveries get slashed by 417,000 acre-feet, Las Vegas shuts down one of its two intakes and Hoover Dam's massive turbines lose the hydraulic pressure needed to generate electricity. The maximum cutback of 500,000 acre-feet kicks in when Mead's surface hits 1,025 feet, or about 20 percent capacity.
Even holding back the maximum 500,000 acre-feet of water -- enough to serve 2 million residents for a year -- accounts for less than a third of the reservoir's current deficit, which is expected to grow as temperatures increase an estimated 2 to 4 degrees Celsius by 2050, as studies predict.
"The cuts that they have proposed are not big enough," said Barnett. Not even close, according to his research. "They're not big enough to cover the climatic effects," he said.
A gamble for Vegas
For Las Vegas, which draws 90 percent of its water supply from the lake, the worst-case scenario would occur if the surface drops below the lower of the city's two intakes to 1,000 feet, cutting off the supply.
The prospect has the Southern Nevada Water Authority pursuing the permits necessary to build a $3.5 billion, 300-mile pipeline to shuttle water from an alternative source in northern Nevada.
Work is already under way on a $700 million project to connect a third intake that would run up through the bottom of the lake, enabling it to be sucked dry. It has been a difficult feat: Last month, construction was halted when workers hit a seam that flooded the excavated cavern. Nobody was injured, although the flood trapped several large pieces of construction equipment underwater.
Scientists and Reclamation officials agree: Las Vegas will not be running dry anytime soon. But that means the spigot on Lake Mead will likely be tightened in the coming years, probably far more than the 2007 agreement calls for.
Even Fulp does not dispute the results of Barnett's most recent study, which predicts that climate change will grow Mead's annual water deficit by as much as 1.5 million acre-feet in 2050, assuming a conservative 10 percent reduction in snow runoff. At 20 percent runoff reduction, the average annual deficit grows by 2 million acre-feet by 2060. According to one of the government's own models, which Barnett cites, Reclamation would be unable to hold Mead's water level above 1,000 feet in a scenario of 20 percent reduction in snowmelt, even if it holds back 3.3 million acre-feet of water.
Studies and models like these prompted Reclamation to launch a two-year study in January that will take a more detailed look at water supply and demand in the region. Fulp said the study will inform decisions about, among other things, how Mead's water gets meted out in the coming decades.
"The risk of losing Lake Mead is negligible," Fulp said. "We're not going to drive this lake into the ground, probably. I don't mean to say it absolutely couldn't happen, but I believe we've got these management options in place so that it wouldn't happen. We would cut deliveries back."