Scientists sometimes refer to the effect a hotter world will have on fresh water as the other water problem, because global warming more commonly evokes the specter of rising oceans submerging great coastal cities. By comparison, the steady decrease in mountain snowpack - the loss of the deep accumulation of high-altitude winter snow that melts each spring to provide nearby regions with most of their water - seems to be a more modest worry.
But not all researchers agree with this ranking of dangers.
In May 2006, for instance, Steven Chu, a Nobel laureate and the director of the Lawrence Berkeley National Laboratory in California, remarked that diminished supplies of fresh water might prove a far more serious problem than slowly rising seas. Chu noted that even the most optimistic climate models for the second half of this century suggest that 30 percent to 70 percent of the snowpack in the Sierra Nevada, which provides most of the water for Northern California, will disappear.
At a hearing in June 2006 before the U.S. Senate, Bradley Udall - an environmental engineer and the nephew of a former U.S. secretary of the interior - stated that Lake Mead, the enormous reservoir in Arizona and Nevada that supplies nearly all the water for Las Vegas, is half-empty, and statistical models indicate that it will never be full again. “As we move forward,” Udall told his audience, “all water-management actions based on normal as defined by the 20th century will increasingly turn out to be bad bets.”
This coming spring, the United Nations Intergovernmental Panel on Climate Change will issue a report identifying areas of the world most at risk of droughts and floods as the earth warms. Many problem zones are located within the United States, including the Colorado River basin - California, Colorado, Utah, Wyoming, New Mexico, Arizona and Nevada - a region encompassing some 30 million people and some of the fastest-growing parts of the country.
Its hard to avoid the conclusion that “something is happening,” as Peter Binney gently puts it.
Binney is a water manager who works for Aurora, Colorado, a city that sprawls over an enormous swath of flat, post-agricultural land south of the Denver airport.
The citys viability depends not on land for expansion - there is plenty of that - but on Binneys wherewithal to conjure new sources of water or increase the output of old ones. Aurora has a population of 310,000 now, Binney said, but that figure is projected to surpass 500,000 by 2035.
Does he have enough water for that many people? “Oh, no,” he replied.
In fact, Binney explained, his job is to figure out how to find more water in a region where every drop is already spoken for - and at a moment when there is little possibility that any more will ever be discovered.
Over the course of a century, Aurora had established a reasonable water supply. About a quarter of its water is piped in from the Colorado River basin about 70 miles, or 112 kilometers, away, which is fed by snowmelt from the Rocky Mountains. Another quarter is taken from reservoirs in the Arkansas River basin far to the south.
The rest comes from the South Platte, a meandering river that runs north through Aurora on its way toward Nebraska.
When Binney arrived in Aurora, in 2002, the city was at the earliest stages of what has since become a nearly continuous dry spell. Though he couldnt see that at the time, he realized Aurora faced a permanent state of emergency if it didnt increase its water supplies. But how?
Among the options available, Binney and the township reasoned that the best was to go some 20 or 30 miles downstream on the South Platte, buy agricultural land near the river, install wells there and retrieve their wastewater.
Thus they could create a system whereby Aurora would use South Platte water; send it to a treatment plant that would discharge it back into the river; go downstream to recapture water from the same river; then pump it back to the city for purification and further use. The process would repeat, ad infinitum.
Many towns have a supply that includes previously treated water. But as far as Binney knew, no municipality in the United States had built the kind of closed loop that Aurora envisioned.
The system, which meant building a 34-mile pipeline from the downstream South Platte riverbanks to a treatment facility in Aurora, would cost $750 million, making it one of the most expensive municipal infrastructure projects in the United States.
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