Colorado River Basin Water Supply and Demand Study

Planners and engineers in the seven-state Colorado River Basin have spent three years and $4 million to forecast water supply and demand scenarios from now through 2060. As part of this, a recently completed (December 2012) 1,500 page was funded by the U.S. Bureau of Reclamation and the seven Colorado River Basin states: the upper basin states of Colorado, New Mexico, Utah, and Wyoming, and the lower basin states of Arizona, California, and Nevada.

The study is an effort to examine a future in which millions more people, along with farms and industry, will compete for river flows diminished by the effects of climate change. Key findings from the study indicate a parched future. “The bottom line is demand is ahead of supply. We are living beyond our means, and the gap is greatest in the Lower Basin,” said David Kanzer, senior water resources engineer for the Colorado River District. “The key assumptions are that demand will go up and supplies will more than likely go down,” Kanzer said. Under the climate change scenario, he said, the forecast is for river flows to fall by 8 to 9 percent. The basin study shows that water use has overtopped supply for the past 10 years, and the gap is forecast to continue. “By 2060, the gap is 3.2 million acre-feet a year, and possibly as much as 8 million acre-feet a year,” Kanzer said.

River flows from 1991 to 2010 past Lee's Ferry, which is just downstream of Glen Canyon Dam in northern Arizona, averaged 13.7 million acre-feet (AF) per year. Current water use in the basin is 16 million to 17.5 million AF per year, Kanzer said, which includes water from tributaries that drain into the Colorado River below Lee's Ferry. Lee's Ferry flows are critical for the upper basin states, as the four states must first send enough water downstream to meet the lower basin's allocations—75 million AF in any 10-year period--and can only use water over that amount. So as snowpack and rainfall declines, it will be upper basin users, and western Colorado in particular, that will face limits in water use. Under some drought scenarios, Kanzer said, “We can run short at Lee's Ferry as soon as 2020--the upper basin shortage risk is real. The Lee's Ferry deficit is real.”