There’s a 50% chance that Lake Mead—a key source of water for millions of people in the southwestern United States—will be dry by 2021 if expected climate changes and future water usage are not curtailed, according to researchers at the Scripps Institution of Oceanography at UC San Diego.
Without Lake Mead and neighboring Lake Powell, the Colorado River system has no buffer to sustain the Southwest’s population through an unusually dry year—or worse, a sustained drought. In such an event, water deliveries would become highly unstable and variable, say research marine physicist Tim Barnett and climate scientist David Pierce.
Barnett and Pierce have concluded that human demand, natural forces like evaporation and human-induced climate change are creating a net deficit of nearly 1 million acre-feet of water per year from the Colorado River system, which includes Lakes Mead and Powell. This amount can supply roughly 8 million people. The scientists’ analysis of Federal Bureau of Reclamation records for past water demand, as well as calculations of scheduled water allocations and climate conditions, indicate the system could run dry even if proposed mitigation measures are implemented.
“We were stunned at the magnitude of the problem and how fast it was coming at us,” Barnett says. “Make no mistake: This water problem is not a scientific abstraction, but rather one that will impact each and every one of us who lives in the Southwest.”
“It’s likely to mean real changes to how we live and do business in this region,” Pierce adds.
The Lake Mead/Lake Powell system includes the stretch of the Colorado River in northern Arizona. Aqueducts carry water to Las Vegas, Los Angeles, San Diego and other Southwest communities. The system is now at only half capacity because of a recent string of dry years, and the team estimates it has already entered an era of deficit.
“When expected changes due to global warming are included as well, currently scheduled depletions are simply not sustainable,” the authors write.
Other recent studies have estimated that climate change will lead to reductions in runoff to the Colorado River system. These analyses consistently forecast reductions of 10%–30% over the next 30 to 50 years, which could affect the water supply of 12–36 million people.
The researchers estimate there’s a 10% chance that Lake Mead could be dry by 2014. They further predict a 50% chance that reservoir levels will drop too low to allow hydroelectric power generation by 2017.
Even if water agencies follow their current drought contingency plans, it may not be enough to counter natural forces, especially if the region enters a period of sustained drought and/or human-induced climate changes, as currently predicted.
Barnett says the team chose to go with conservative estimates of the situation, though the water shortage is likely to be more dire. The team based its findings on the premise that climate-change effects started only in 2007, though most researchers consider human-caused changes in climate to have likely started decades earlier.
“Today, we are at or beyond the sustainable limit of the Colorado system,” their report concludes. “The alternative to reasoned solutions to this coming water crisis is a major societal and economic disruption in the desert southwest—something that will affect each of us living in the region.”
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