Reslicing a smallish pie: Changes for the shrinking Colorado River
by Allen Best
What gives on the Colorado River? A recent study in Colorado, which provides half of the water in the river, found no trend in precipitation. Yet reservoirs on the river and its tributaries, especially the giant impoundments of Mead and Powell, have been declining such that water agencies from Denver to Los Angeles have formulated emergency measures.
Eric Kuhn suspects that rising temperatures—such as are predicted by climate change models—may explain at least part of this discrepancy. In other words, we’re seeing the future happen before our eyes as water levels in the reservoirs drop.
“We are seeing a declining long-term average inflow, and that is where I don’t think there has been any research,” said Kuhn, general manager of the Colorado River Water Conservation District, in an interview.
Kuhn would like to see statistical studies that examine the link between rising temperatures in recent decades, increased evaporation and transpiration, and reduce flows of rivers in the Colorado River Basin.
Conducting this research would not be easy, he said, as determining natural flows of rivers is a “tough calculation,” due to the many diversions.
Also in play may be the dust-on-snow phenomenon. Research during the last decade in Colorado’s San Juan Mountains has revealed the impact of wind-borne dust on snow. With the dust from winter and spring storms on the snow, it melts more rapidly. The snow is more vulnerable to evaporation through a process called sublimation and more water is also lost through transpiration. See National Snow & Ice Data Center story.
Studies by Tom Painter and others (and assisted by the Center for Snow & Avalanche Studies) has suggested that dust on snow may be causing the loss of 5 percent of water in the Colorado River to evaporation/sublimation and transpiration. A study by Janice Brahney, formerly of the University of Colorado and now of the University of British Columbia, further documented increased dust-on-snow depositions since the 1990s. The dust is believed to be the result of more intense use of lands in the desert Southwest.
Why does this matter? In a recent presentation in Ouray before the Colorado Association of Ski Towns, Kuhn sketched out the big picture of the Colorado River. It is literally a river with nothing left over.
The average flow of the Colorado River is 15 million acre-feet. This compares with 16.5 million acre-feet for the Hudson River, 164 million for the Columbia, and 520 million for the Mississippi River. All except the Colorado routinely flow almost entirely into the oceans.
Since 1998, none of the Colorado made it into the Pacific Ocean—until last year. But the feat required special circumstances. Kuhn doesn’t expect it to happen often—if ever.
“What we don’t know is whether that will happen just once, or whether it will happen again,” he said.
Too, Kuhn sees a zero-sum situation. “When somebody uses more, somebody else will use less,” he observes
Agriculture currently uses a majority of water, but Kuhn sees a reduction in coming decades. Currently, the Colorado River Basin and adjoining areas—including Denver, Cheyenne, Salt Lake City, Albuquerque and Los Angeles—have 35 million people who depend, at least in part, on water from the basin. That will grow to 80 million.
The Colorado River currently irrigates 4.6 million acres, which is likely to decrease by 15 percent in coming decades. Much of that will be due to new houses and other municipal development on existing agriculture lands. This is particularly prominent in Arizona. However, there will also be continued purchase of farms for their water rights, what is called buy-and-dry.
The most dynamic growth will occur not in the Colorado River Basin, but in adjacent areas.
This will include Colorado. The Western Slope—which is drained by the Colorado River—currently has 500,000 people and is projected o grow at a 7 percent clip. The Front Range of Colorado is projected to grow more slowly, at around 5 percent, but from a much larger base of 4.3 million people. As such, most of Colorado’s growth will be outside of the Colorado River Basin—but dependent upon water from the basin.
Much of that future population growth will be accomplished by reallocating existing water diversions. That transition is well underway. For example, the Colorado-Big Thompson project diverts water from Grand Lake to the Fort Collins-Boulder-Greeley area. When constructed in the 1950, 85 percent of that water was used for agriculture purposes and 15 percent for urban uses. Today, only a third goes to agriculture, with two-thirds used for municipal and industrial purposes. In northern Colorado, as elsewhere, most of the municipal water is devoted to irrigation of landscaping turf.
This same transfer has occurred within the context of mountain valleys. In the Roaring Fork Valley from Aspen to Glenwood Springs, today there are a few ranches tied up in conservation easements and a whole lot of golf courses.”
In coming decades, water uses will continue to be transferred. Within agriculture, for example, remaining water may be used for more high-value crops, such as vegetables, as compared to low-value crops, such as hay for livestock.
A more advanced market mechanism might help expedite the transfer of water uses. “Many people don’t want to see a market solution,” he observed.