Refilling of Colorado River lakes all but unthinkable, experts say

This year’s extremely heavy snowpack in the river’s Upper Basin states will produce the river’s second highest annual flow of the 21st century, federal forecasts show. The river is expected to bring 18.6 million acre-feet of water to Lee’s Ferry, lying between Glen Canyon Dam and the Grand Canyon in northern Arizona, the U.S. Bureau of Reclamation predicts.

The flow is likely to be 80% to 140% greater than the river has carried in any of the previous three years, federal records show.

But given the reservoirs’ precarious conditions, with both carrying 25% to 30% of their capacity today, it would take another four or five consecutive years of high flows like this one to fill Powell and Mead again, said Brad Udall, a Colorado State University climate scientist, and Eric Kuhn, a water researcher and former general manager of the Colorado River Water Conservation District in Glenwood Springs, Colo.

That’s highly unlikely or impossible, with the river carrying about 20% less water, on average, each year than it did during the 20th century, Udall and Kuhn said.

“We’re in a century with extreme climate change that is reducing flows in most years due to human-caused increases in heat,” Udall said.

Officials in Reclamation’s Upper and Lower Basin offices didn’t respond to questions from the Star about whether they agree with Udall and Kuhn’s gloomy outlook for the lakes.

But at a federally sponsored webinar held Tuesday, May 9, Paul Miller, a hydrologist for the federal Colorado River Basin Forecast Center, said he believes it could take even six to eight years like this one to refill all the reservoirs in the river’s Upper Colorado River Basin, plus Lake Mead in the Lower Colorado River Basin — “which probably isn’t very likely.”

Miller noted that Jennifer Pitt, a longtime Colorado River activist for the National Audubon Society, has recently concluded that “if we had normal snowpack conditions for three straight years and also zero water use, we’d refill the majority of the Upper Colorado Basin reservoirs.” Miller based his six- to eight-year estimate on Pitt’s logic, but “knowing we are not ever going to not use water.”

The webinar was sponsored by the National integrated Drought Information System, a branch of the National Oceanic and Atmospherics Administration. A second speaker, Andrew Hoell, a research meteorologist for NOAA’s physical sciences laboratory, said Miller’s “back of the envelope calculations” are realistic.

While the lack of soil moisture due to hot, dry springs and summers has repeatedly held down runoff into Lake Powell in recent years, this year, “Things are copacetic now. They’re great,” Hoell said.

“The snow is going to run off and replenish the soil moisture. But it will take longer for reservoirs to recharge. They need the sustained behavior for many years. We need to go into a wet regime to refill those reservoirs.”

The reservoirs are in bad enough shape that the bureau is studying two alternatives for curbing consumption of river water by the Lower Basin states of Arizona, California and Nevada by 2 million to 4 million acre-feet a year. Such a cut, starting next year, would be equivalent to up to nearly 30% of current levels of use.

Such reductions are needed to insure the lakes don’t fall so low that their dams can no longer generate electricity, let alone to “dead pool,” in which no water could be extracted from them, bureau officials have said.

The bureau is expected to announce a final decision on cuts by August. Arizona and the six other river basin states’ water officials are trying to negotiate their own agreement to avoid taking more draconian, federally imposed reductions.

But the reservoirs’ situation may not be hopeless even if they don’t refill. Even in today’s drier climate, it’s still possible the river could get enough consecutive years of better than average flows — as occurred during the late 1990s — to give the Colorado a breather and stave off drastic cuts for awhile, Kuhn and Udall said. While such a string of wet weather years wouldn’t fill the lakes, they would lift their levels to at least half full.

The river carried 21.6, 16.6 and 15.8 million acre-feet a year, respectively, from 1997 through 1999. All three flows were well above the…