Winter storms have blanketed the mountains on the upper Colorado River with snow. But even this year’s above-average snowpack won’t be nearly enough to make up for the river’s chronic overallocation, compounded by 19 years of drought and the worsening effects of climate change.
Lake Powell and Lake Mead, the country’s two largest reservoirs, are now at just 40 percent of full capacity. The reservoirs have together been at their lowest levels since Glen Canyon Dam was built and Lake Powell was filled in the 1960s.
A shortage could be declared at Lake Mead starting next year, leading to water cutbacks in parts of the Southwest. And while it’s not yet clear whether Mead will sit below the trigger point for a shortage at the end of the year, federal water managers say chances are the reservoir will cross that critical threshold for the first time.
The latest projections from the federal Bureau of Reclamation this month show a 69 percent chance of a shortage in the river’s Lower Basin in 2020.
“Although this year’s precipitation levels and snowpack are currently above average and trending in the right direction throughout much of the basin, it would take multiple above-average years for the storage conditions to recover from the drought,” Bureau of Reclamation spokeswoman Patti Aaron said in an email. She pointed out that the drought, which started in 2000, has been the driest 19-year period in more than a century of record-keeping.
Drought plan is ‘a Band-Aid’
Federal officials have been pressing for California and Arizona to finish their pieces of a proposed three-state deal, the Drought Contingency Plan, which would involve taking less water out of Lake Mead during a shortage to prevent the reservoir from falling even further.
But whether all the pieces will fall into place to complete the deal isn’t clear. And water managers throughout the Southwest acknowledge the proposed agreement is merely a stopgap measure aimed at getting through the next few years, while bigger decisions await on how to balance the supply and demand of water over the long run.
“The Drought Contingency Plan is a Band-Aid, and that’s all it is,” said Jonathan Overpeck, a climate scientist and dean of the University of Michigan’s School for Environment and Sustainability. “It does bring people to the table to find ways to reduce water use and share in the burden of reducing water use. But it doesn’t address the cause of the water reductions. It doesn’t address the cause of the growing water shortages.”
The Colorado River irrigates more than 5 million acres of farmland and supplies about 40 million people in cities from Denver to Los Angeles.
The legal framework that divvies up the river was established during much wetter times nearly a century ago, starting with the 1922 Colorado River Compact. That and subsequent agreements have committed more water than what flows in the river in an average year, leading to what experts call the river’s “structural deficit.”
Scientific research has also shown that rising temperatures during the past two decades have intensified the drought and taken a major toll on the river’s flow. The higher temperatures have shrunk the average snowpack in the mountains, reduced the flow of streams, and increased the amount of water that evaporates off the landscape.
In one study last year, scientists estimated that about half the trend of decreasing runoff is linked to unprecedented warming.
Much of the Colorado River’s flow comes from rain and snow falling in the river’s Upper Basin, which stretches from Wyoming to New Mexico.
Measurements from snow sensors show that, depending on the region, the snowpack now ranges between 101 percent and 148 percent of the historical average.
Since the gates of Glen Canyon Dam were closed in 1963, the ecology of the Colorado River in the Grand Canyon has been altered, some fear forever. David Wallace and Michael Chow/The Republic, Arizona Republic
While the snowpack looks good so far, Overpeck said, it could quickly dissipate if March and April turn out to be warmer than average, which has often been the case during the past couple of decades.
“We should be cautious,” Overpeck said. “The old adage is hope for the best — in this case, lots of snow — plan for the worst — in this case, continued impacts of global warming and lower streamflow.”
Overpeck said he suggests people in Arizona and the Southwest should be looking for ways to conserve more and more water into the future, while also seeking to curb emissions of planet-warming greenhouse gases.
“The only way they’re going to get out of never-ending reductions in river flow is to stop climate change, stop global warming, stop the burning of fossil fuel,” Overpeck said. “We’re treating the symptoms of the illness rather than the cause of the illness. The illness, in terms of the Colorado River, is climate change.”
Since 2000, the amount of water flowing in the Colorado River has dropped 19 percent below the average of the past century.
Arizona gets nearly 40 percent of its water from the Colorado River.
The state also draws water from the Salt and Verde rivers. And after storms brought rain and snow this month, Salt River Project estimated its reservoirs on the Salt and Verde rivers will fill to 75 percent of capacity this year.
Snowpack is not as reliable anymore
On the Colorado River, the picture is very different. A shortage would be declared at Lake Mead in 2020 if federal officials determine that the lake’s level will be below elevation 1,075 feet at the start of the year. The reservoir is now just above that level, at 1,087 feet.
One important factor behind the imbalance is the “structural deficit,” which remains despite efforts in the Lower Basin to reduce demand for water, said Anne Castle, a senior fellow at the University of Colorado’s Getches-Wilkinson Center for Natural Resources, Energy, and the Environment.
“The reductions have simply not been sufficient to date to overcome the structural deficit,” Castle said. “Second, climate change and warmer temperatures mean that snowpack doesn’t translate into runoff in the same way as it did in the past.”
Last year was also extremely dry, leaving the soil depleted of moisture in many of the watersheds that feed into the Colorado River.
Castle, who was the Interior Department’s assistant secretary for water and science from 2009 to 2014, said the Drought Contingency Plan represents a huge step forward, but it’s not a complete solution because it only addresses the imbalance between the inflow and outflow of water when Lake Mead is at very low levels.
“If you look at it that way, it kind of ensures that Lake Mead will stay at those very low levels, because as you rise out of the shortage levels, then the… contributions to Lake Mead don’t have to take place,” Castle said. “And so, we’re sort of back to where we were in terms of having a structural deficit.”
The proposed drought plant lays out a framework for California, Arizona and Nevada to share in water cutbacks between 2020 and 2026. Another round of more complex negotiations is scheduled to begin next year on a new set of rules for managing shortages, which would take effect after 2026.
“All of us in the seven Colorado River basin states are going to have to adjust to the new reality of aridification in the basin that results in lower flows,” Castle said. “The longer-term conversation has to be about, how do we live within our means in the Colorado River basin, at all levels in Lake Mead, so that we have a more sustainable system?”