FLOOD AND DROUGHT: Upper regions of the Colorado River face floods while the lower endure drought, which could presage unstable water supplies for the western U.S. Image: Wolfpack306/Wikimedia Commons
The Colorado River has a long journey. It flows from mountains, runs by cities, winds through remote, rust-colored canyons and touches seven states before entering Mexico. It's a natural wonder, but also a life source of the more than 30 million people who rely on it.
But in recent years, the Colorado River has become less reliable. Since 1999, abnormally low precipitation totals and hot and dry conditions have brought reservoir water levels close to record lows. The multiyear drought, the most severe since documentation began more than 100 years ago, has put the water supply in the thirsty Southwest in jeopardy.
This year, heavy snowpack and spring precipitation have brought the region some relief by partially refilling the reservoirs. But while National Oceanic and Atmospheric Administration research shows that snowmelt runoff into the upper basin hasn't been this high since 1986, the southern end of the Colorado River continues to stop shy of the Sea of Cortez, where it used to run until the late 1990s.
The paradox is that this season stands in such stark contrast to the past 11 years of drought, highlighting the types of variability that climate change can wreak on the hydrological cycle.
"It's not at all uncommon for the basin to have high runoff years in a longer period of drought," said Pamela Adams, outreach coordinator with the Bureau of Reclamation, the body that manages the Colorado River Basin. "We can see that in both the past 100 years of data, plus you can see it in the tree-ring data."
The Bureau of Reclamation released the first of three interim reports last month as part of its broader Colorado River Basin Water Supply and Demand Study. The report is designed to provide an outlook on the next "highly uncertain" 50 years (until 2060) of the river's life. Authors wrote that in the nearly quarter-million-square-mile Colorado River Basin, "climate change, record drought, population increases and environmental needs" are likely to make water supplies ever scarcer.
One scenario already found that the mean natural flow at Lees Ferry, Ariz., is projected to decrease by 9 percent over the next 50 years and experience an increased frequency and duration of drought.
Understanding the supplies, demands and risks
The Colorado River is vital to all of the seven states touching the basin -- Arizona, California, Colorado, New Mexico, Nevada, Utah and Wyoming. Apart from providing water for municipal use, the river irrigates 4 million acres of land and sustains 15 Native American tribes, seven National Wildlife Refuges and 11 National Parks, according to the basin study. Hydropower stations along the Colorado River supply more than 4,200 megawatts of generating capacity.
It is also a significant resource for Mexico, because the United States is legally required to ensure its southern neighbor receives 1.5 million acre-feet -- the unit used to measure water resources -- of water annually.
"What this is trying to do is help us think about the possible ways the future will evolve along the Colorado River," said Adams of the Colorado Basin report. "We're looking at scenarios and get a range of possible futures and understand a range of supply and demand so we get a range of what the balances may be."
Previous environmental impact statements have been focused on managing supply, said Adams. This new report, scheduled for completion by July 2012, will for the first time focus on understanding demand because of the effects of climate change. The study is based on data from historically observed and paleo-reconstructed water flow records, as well as projections from global climate models.
"Concerns regarding the reliability of the Colorado River system to meet the future needs of Basin resources in the 21st-century are heightened, given the likelihood of increasing demand for water throughout the Basin, coupled with projections of reduced supply due to climate change," wrote the authors of the report.