18 March 2008—Up to 30 million people in seven western U.S. states—Arizona, California, Colorado, Nevada, Utah, Wyoming, and New Mexico—could begin to experience water shortages and power outages as soon as 2013, according to a study published in the January edition of the journal Water Resources Research . ”Our hydrological analysis of Lake Mead and Lake Powell shows there is a 10 percent chance that water levels in the man-made Lakes Mead [in Nevada] and Powell [on the Utah/Arizona border] will be so low by 2013 that they might not be able to meet water-supply demands nor produce the hydroelectric power needed in the Southwest,” says Timothy Barnett, a research marine physicist at the Scripps Institution of Oceanography in La Jolla, Calif., and lead author of the Water Resources paper. Barnett’s team also found that there is a greater than 50 percent chance that power-pool levels—the minimum depth of water at which hydroelectric power can be generated—will be reached in 2017. But the agency that manages the region’s river system disputes the study’s conclusions and says that despite a drought, Lake Mead still has a 20-meter cushion before the lights go out.
The waters stored in the Lake Mead and Lake Powell reservoirs are the source of hydroelectric power produced by the Hoover and Glen Canyon Dams for seven states and together produce about 10 000 gigawatt-hours of electricity. The water source for the dams is the Colorado River, which begins its long journey from the snow-capped Rocky Mountains in Colorado. The natural runoff from snowmelt replenishes the water in the 2330-kilometer-long Colorado River each spring and summer. After running through the turbines at the Hoover Dam on Lake Mead, the Colorado River continues on its journey southward to the Davis, Parker, and Imperial dams all located along the California/Arizona border.
From 2000 to 2008, the Colorado River has been steadily declining for three reasons, according to Barnett: a major ongoing drought in the region; the way the Colorado Bureau of Reclamation is taking out more water than nature is putting back in; and global climate change caused by greenhouse gases. For the purpose of this research, Barnett conservatively assumed global warming in the Southwest began in 2007, although in reality it has been occurring in the Southwest for decades, he says.
”If you look at the water-usage figures in our paper, the water usage of the Colorado River has been going almost vertical along with the population growth. Our analysis shows that even without any climate change factored in, Lake Mead will go dry by 2021.” In the research paper, Barnett’s team defines ”going dry” as the level of water in Lakes Mead and Powell being so low that they can no longer be used to generate hydroelectric power.
Not everyone agrees with Barnett’s analysis, though. Robert Walsh, an external affairs officer for the Bureau of Reclamation on the Lower Colorado Region, the agency that manages the region’s rivers, says, ”The Scripps Institution paper merely projects that Lake Mead could ’run dry’ by 2021—our own studies do not show that, and we do not agree with the paper.” In the summer of 2005, the Bureau of Reclamation initiated a public process to develop guidelines for shortage conditions in the Lower Colorado River Basin and for the coordinated operation of Lake Powell and Lake Mead under a wide range of hydrological conditions. ”In order to develop these shortage and coordinated operations guidelines, we performed numerous modeling runs to assess potential future hydrologic conditions on the Colorado River. None of our modeling runs showed Lake Mead ’going dry,’ ” says Walsh. He also says the impact of hydropower on the region has been mischaracterized. Although Lake Mead serves 23 million to 25 million people with water, the number served by hydroelectric power from the Hoover Dam is probably less than one-fifth of that, because most of Hoover’s power is used for commercial, not residential, purposes.
In February, the water level in Lake Mead was at 340 meters above sea level, or 17 meters below average. The power-generation capacity at Hoover Dam is 2080 megawatts but has been steadily reduced by the drought. With all generators operating, the plant’s current rated capacity will be about 1655 MW into the spring of 2008. ”We would probably be able to continue generating power down to a water elevation of [320 meters] above sea level in Lake Mead, and it is theoretically possible to generate power below that level, but that could cause generator damage,” says Walsh.
Meanwhile, Barnett says he stands by his findings. ”The environmental impact statement released by the Bureau of Reclamation in the Lower Colorado River assumes operations on the Colorado River for the next 50 years without factoring in any climate change information. This is what led me and my colleague David Pierce—also from Scripps—to look at the water budget of the Colorado system,” he says.
”There are a lot of ifs here,” counters Walsh. ”Obviously, one can do studies and run models and make projections forever, but we can’t foretell the future with any degree of certainty.”