The Uncertain Future of Phoenix and Las Vegas
As the Colorado River dries up, Southwestern cities may be doomed
The American Southwest is running out of water. For a powerful reminder, if any is needed, of why builders in Western states should integrate water-conservation strategies in all new buildings, check out a new book by James Lawrence Powell, Dead Pool: Lake Powell, Global Warming and the Future of Water.
Powell’s message is stark: according to scientists’ best predictions, millions of Americans living in the Southwest will face unprecedented water shortages in the next few decades.
Only half full
The rapid growth of Southwestern cities was made possible by two huge Colorado River projects undertaken by the U.S. Bureau of Reclamation: the Hoover Dam, completed in 1935, and the Glen Canyon Dam, completed in 1966.
Although the two reservoirs created by these dams, Lake Mead and Lake Powell, allowed millions of Americans to move to the desert, Colorado River water is now being consumed at such a high rate that the reservoirs are rarely full. At the end of October 2007, Lake Powell and Lake Mead each held only 49 percent of capacity.
A resource to be exploited
For decades, the Bureau of Reclamation’s predictions of Colorado River flow have been based, to put it charitably, on wishful thinking and junk science.
Powell shows how federal bureaucrats and politicians used flagrant exaggerations to promote dams on the Colorado River. Powell writes, “As experience accumulated, it became apparent that not only did the agency routinely underestimate costs, it did so by at least a factor of two.”
The taxpayers ended up footing the bill for dams that supply farmers with subsidized water that costs far more to deliver than the value of the resulting harvests justifies. Powell concludes that these massive Western water projects amounted to “a kind of hydraulic Ponzi scheme.”
During most of the twentieth century, the Bureau of Reclamation, using language that harkened back to the early years of the industrial revolution, proclaimed a philosophy of raw exploitation. For example, in a 1946 “Blue Book” report to Congress, the Bureau declared, “Yesterday the Colorado River was a natural menace. … Today this mighty river is recognized as a national resource. … Tomorrow the Colorado River will be utilized to the last drop.”
Sadly, the Bureau’s boastful 1946 prediction has come true.
Wet years were the basis for a misleading benchmark
Even sixty years ago, as senators and representatives were reading the triumphant Blue Book report, it was already clear that the Bureau’s 1922 Colorado River Compact allocated more water to Western states than the river carried. It turns out that the Compact’s optimistic water-flow projections were based on measurements made during the unusually wet years preceding 1922, when the river’s annual flow averaged 21 million acre-feet (MAF).
Current Colorado River allocations are based on a presumed annual flow of 16 MAF. Yet according to the best scientific consensus — established in part by tree-ring studies — the flow of the Colorado River over the last 450 years has averaged only 14.6 MAF per year. Powell concludes, “Today — not sometime in the future after global warming has reduced supply — the surpluses on which the basin states have long counted are gone.”
Alice in Wonderland
Virtually every drop of the Colorado River is now piped away for human use; the lower reaches of the river often dry up entirely before reaching the sea. In coming decades, however, the situation will only worsen. “Regardless of the state of the Colorado River today, every city, county, and state in the West plans to consume more water,” Powell writes. “In defiance of logic and limits, the driest states have become the fastest growing.”
Meanwhile, global climate change is causing a noticeable reduction in the river’s flow. “The flow of the Colorado River during the twenty-first century dropped so much faster than the experts thought possible that by 2004, Lakes Powell and Mead together held 20 MAF less than their worst-case forecast,” Powell writes. “Including the relatively wet 2005, the average inflow to Lake Powell during the first eight years of the twenty-first century is down by an average of 40 percent [from the twentieth-century average].”
Although there is strong scientific evidence that the heavy Colorado River flows of the twentieth century are unlikely to return, the Bureau of Reclamation’s projections haven’t been adjusted to reflect current knowledge. “Using the bureau’s preferred method of operating the Colorado River system, its modeling projects that Lake Powell will gain water between now and about 2030,” Powell writes. “All of this has a certain through-the-looking-glass quality. … The new shortage guidelines, resting as they do on the bureau’s flawed computer modeling, are like a Potemkin village of water planning.”
Meanwhile, temperatures are rising…
Even if the global climate stays stable, the Southwest will face serious water shortages. Yet average temperatures are already rising; as a result, Southwestern cities face a catastrophic future.
If precipitation levels don’t decline — an optimistic scenario — higher temperatures will still cause an increase in evapotranspiration from mountain vegetation, reducing runoff. “If precipitation remains constant while evapotranspiration increases by just 2 percent, runoff declines by nearly 14 percent,” Powell writes. Moreover, “warmer temperatures not only melt snow, they cause it to sublimate — to pass directly from solid into vapor without going through the liquid phase.” These two mechanisms — evapotranspiration and sublimation — tend to multiply the drought-causing effects of rising temperatures.
As the Colorado River dries up, Powell predicts, the buildings and swimming pools of Las Vegas, Phoenix, and Tucson are destined to be abandoned. Though startling, Powell’s prediction is well supported by the available evidence.
Dead Pool: Lake Powell, Global Warming, and the Future of Water in the West, by James Lawrence Powell, is available from the University of California Press.
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