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The city is one of the largest in the Colorado River basin, but its share of the river is relatively small when officials allocated the Colorado’s water to different states in 1922, no one expected so many people to be living in the Nevada desert. Mulroy is also general manager of the Southern Nevada Water Authority, which serves two million people in greater Las Vegas. “It’s not abundant, it’s not reliable, it’s not going to always be there.” People need a “fundamental, cultural attitude change about water supply in the Southwest,” she adds. “There’s not enough fresh water to handle nine billion people at current consumption levels,” says Patricia Mulroy, a board member of the Colorado-based Water Research Foundation, which promotes the development of safe, affordable drinking water worldwide. More than one billion people around the world now live in water-stressed regions, according to the World Health Organization, a number that is expected to double by 2050, when an estimated nine billion people will inhabit the planet. In southwestern Australia, which is in the midst of its worst drought in 750 years, fresh water is so scarce the city of Perth is building plants to remove the salt from seawater. In the Andes Mountains of South America, glaciers are melting so quickly that millions of people in Peru, Bolivia and Ecuador are expected to lose a major source of fresh water by 2020. Other regions-the Mediterranean, southern Africa, parts of South America and Asia-also face fresh-water shortages, perhaps outright crises. “You’re going to see earlier runoff and lower flows later in the year,” so water will be more scarce during the growing season, says Udall. Higher overall air temperatures will mean more water lost to evaporation. Less precipitation in the Rocky Mountains will yield less water to begin with.

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Water resource officials say some of the reservoirs fed by the river will never be full again.Ĭlimate change will likely decrease the river’s flow by 5 to 20 percent in the next 40 years, says geoscientist Brad Udall, director of the University of Colorado Western Water Assessment. But at the lake’s edge they can see lines in the rock walls, distinct as bathtub rings, showing the water level far lower than it once was-some 130 feet lower, as it happens, since 2000. And boaters still roar across Nevada and Arizona’s Lake Mead, 110 miles long and formed by the Hoover Dam. It still tumbles through the Grand Canyon, much to the delight of rafters and other visitors. The river has been running especially low for the past decade, as drought has gripped the Southwest. The damming and diverting of the Colorado, the nation’s seventh-longest river, may be seen by some as a triumph of engineering and by others as a crime against nature, but there are ominous new twists. states and Mexico, with 70 percent or more of its water siphoned off to irrigate 3.5 million acres of cropland. The river now serves 30 million people in seven U.S. Then, beginning in the 1920s, Western states began divvying up the Colorado’s water, building dams and diverting the flow hundreds of miles, to Los Angeles, San Diego, Phoenix and other fast-growing cities. That is, it did so for six million years. From its source high in the Rocky Mountains, the Colorado River channels water south nearly 1,500 miles, over falls, through deserts and canyons, to the lush wetlands of a vast delta in Mexico and into the Gulf of California.

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