Requiem for a River

(Page 3 of 5)

In December 2007, the seven states agreed to new conservation guidelines proposed by the Bureau of Reclamation. The new rules let states save their unused water. Water banking, as it's called, is intended to encourage conservation; states can put away water for future dry years or trade stored water among themselves. The rules also impose what amounts to a "water tax," which allows the bureau to retain 8 percent of the states' banked water in Lake Mead to offset withdrawals and evaporation. The new guidelines also specify how the states will share the burden of shortages if -- or when -- the reservoirs can't deliver in full.

The reforms are crucial, Fulp says. "We can store four times the river's average annual inflow in Powell and Mead, which is why we have been able to get through this drought without significant water shortages. When we walked into this drought in 1999, we were fortunate to have a relatively full system. That may not always happen."

In fact, the odds of that happening again are not good. Studies of the Southwest's past climate show that the twentieth century was anomalously wet. Ironically, the years leading up to the signing of the Colorado River Compact were among the wettest the region has ever known.

Tucson, Arizona
[Elevation 2,389 feet]

There's a treasure beneath the bleachers of the University of Arizona's football stadium. In a dusty warren of rooms that share corridors with concession stands and storage lockers is the university's Laboratory of Tree-Ring Research, home to the world's largest collection of dated wood samples.

"This is not simply a University of Arizona collection. This is a world heritage collection. It's unique," says Rex Adams, the public face and de facto curator of the collection. "It contains a record of environmental history for the last 8,800 years." Adams, a compact man with a trim gray beard and thinning gray hair, is leading me down aisles that wend through boxes of wood samples piled to the ceiling. Outside, the city shimmers in the heat of a spring morning; yesterday the temperature in Tucson hit a new all-time high for April.

"Just across the way is the international collection. You can see material here from South Africa, Australia, New Zealand, Argentina," Adams says, his voice fading momentarily as he disappears down a cool, dark cardboard-box canyon. "We've had researchers come from some of these places and ask, ‘Do you have a specimen from the mid-1970s, because we don't have that forest anymore.'"

Andrew Ellicott Douglass, an astronomer at Lowell Observatory in Flagstaff, started the collection in 1904, hoping to find evidence of sunspot cycles in tree rings. He never succeeded in that quest, but he founded the modern science of dendrochronology by precisely matching tree-ring samples to specific calendar years. Today the lab houses more than a million wood samples from more than 10,000 sites around the world.

"The single most important aspect of dendrochronology is the ability to provide absolute dates," Adams tells me. "If we say this year is 1748, it is 1748 -- not 1747 or 1749."

Researchers here have used tree-ring data to reconstruct the Colorado River's flow for much of the past several hundred years. And that written-in-wood record tells a story very different from that of the data collected with river-flow gauges, which cover only the past century. When the Colorado River Compact was signed, 20 years of measurements suggested that the river's average annual flow was 16.4 million acre-feet. (One acre-foot equals 325,851 gallons, the amount of water that would cover one flat acre to a depth of one foot.) A family of four typically uses about half an acre-foot of water in a year. Lakes Mead and Powell now hold about 25 million acre-feet between them.

The tree-ring record for the Southwest shows that the years from 1900 to 1922 were probably the wettest of the past 500 years; in the recent drought the river's annual flow has plummeted as low as 3.8 million acre-feet. In short, states have been allocated more water than the river actually contains.

David Meko, a hydrologist at the tree-ring lab, has looked as far back as anyone into the river's past. Water managers don't like to think about his research, which shows that droughts far more severe than today's have afflicted the Southwest, although those past droughts differed from the current one in one crucial respect: they ended.

"The Colorado basin had worse droughts during the medieval years," Meko says. On his computer he shows me some precipitation graphs derived from tree-ring studies. "This drought," he says, pointing to a span that began in 1121, "lasted around 60 years. It's really unusual for not having any very wet years. That would be important for the Colorado River today, because we rely on those wet years to fill the reservoirs. So now we're sitting around waiting for one of those to come along again, and it's not happening. Those very wet years may not be coming anymore; the climate of the Southwest may be moving into an almost perpetual period of drought."

A few days before my meeting with Meko, the journal Science published a startling paper by a team of climatologists from several universities. The researchers took 19 of the world's leading computer climate models and used each to project the Southwest's climate for the remainder of the century. I spoke with one of the paper's authors, Richard Seager, of the Lamont-Doherty Earth Observatory at Columbia University in New York City.

"We plotted the results for all the models one at a time and found that they were all doing the same thing," Seager told me during a telephone interview. "I was shocked when I saw the results." Almost every model predicted that a state of severe drought will become the norm for the entire Southwest. All of them show that the storm tracks that bring moisture to the region -- that is, the winds that drop the snow that feeds the Colorado River -- will be shifted northward by global warming. When I asked Seager about this permanent megadrought, he corrected me.

"You could call it permanent drought, but drought is a term that implies an anomalous dry period. It's really a shift to a drier mean climate. No one says the Sahara is having a drought."

Unfortunately, none of the climate models has been refined to the point where water managers in the Southwest could use it to plan precisely for shortages. For now, state and federal agencies are in the disconcerting position of relying on measurements of the Colorado River's flow for the past 100 years to gauge the future, even as it becomes increasingly clear that those past flows will never come again.

So how dire is the outlook for the Southwest? Could Lake Powell drop another 150 feet, as it did between 1999 and 2004, leaving Las Vegas high and dry? Tom Ryan, the Bureau of Reclamation hydrologist, told me in a telephone interview last December that the situation is serious but manageable. The drought has forced change on the region, he said. During its first few years, the states of the Southwest continued to operate as they had for most of the previous decade, when the system had a surfeit of water. The early failure to recognize the magnitude of the drought exacerbated the problem.

"There was still this mentality that the reservoirs were pretty full and we could just use whatever we needed to meet our demand," Ryan told me. "That mentality has obviously changed. And we've gone to normal deliveries, away from surpluses." The days of releasing 8 million acre-feet of water to the lower basin states are over, at least for now; the figure has been scaled back to 7.5 million acre-feet annually.

After eight years of the worst drought of the past 100 years, both Lake Mead and Lake Powell are still nearly half full. While the two reservoirs may never again be completely full, Ryan said it's unlikely they'll get so low that a cutoff of water to any of the region's cities would occur. Some straightforward conservation measures would probably prevent that calamity. Even now, in the midst of a drought, the cities of the Southwest are still wasting water. According to a study by the Pacific Institute, a California-based think tank, Las Vegas alone could save 86,000 acre-feet of water annually -- nearly 30 percent of Nevada's total allotment from the Colorado River-with the installation of water-efficient fixtures and appliances in homes and hotels. And of all the cities in the Southwest, none is more vulnerable to the vicissitudes of drought.

Las Vegas, Nevada
[Elevation 2,001 feet]

Sin City. Pathetically easy to vilify. Where else, outside of an oil emirate, would there exist anything like the illuminated fountains at the Bellagio Hotel, jetting melted mountain snow 240 feet into the hot Mojave air, the nightly eruptions pulsing in time to music? Or for more "Desert? What desert?" attitude, take a stretch Hummer down the Strip to the Mandalay Bay Resort and Casino, with its 11-acre beach, rolling artificial surf, and cabanas.

But in truth, when it comes to water, the city-and the entire state of Nevada-have been shortchanged. The Colorado River Compact gives Nevada just 300,000 acre-feet each year, the smallest allotment of any state. California receives more than 10 times Nevada's share, and Lake Mead loses twice as much each year to evaporation alone.

Las Vegas has no more ardent advocate than Pat Mulroy, the driven, get-to-the-point general manager of the Southern Nevada Water Authority. Mulroy is one of the most powerful people in the Southwest. No one here would be surprised to see her occupy the governor's mansion in Carson City someday.

"The Las Vegas Strip uses 3 percent of southern Nevada's water, but it is the biggest economic engine in the state," Mulroy tells me. We're in her spacious office not far from the Strip. She's sitting behind a polished desk so big it would be classed as a light truck if it had wheels. She's well tanned, has elegantly coiffed, thick silver hair, and wears a chic pantsuit with a high-necked white sweater. Every few minutes she cants forward in her seat, speaking forcefully for emphasis.

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