Smithsonian Magazine profiles the river and looks at how declining freshwater resources are threatening the vast and growing cities that depend on the river.
"Climate 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. Less precipitation in the Rocky Mountains will yield less water to begin with. Droughts will last longer. Higher overall air temperatures will mean more water lost to evaporation. '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."