Those tentative conclusions are found in the draft Colorado River Water Availability Study, a $1 million effort described by state water officials, who commissioned it, as cutting edge.
“I don’t know of any other state that is putting the time, resources and money into this,” said Jennifer Gimbel, executive director of the Colorado Water Conservation Board, a state agency charged with overseeing protection and development of Colorado’s waters. About three-quarters of the state’s water originates west of the Continental Divide, in the headwaters of the Colorado River and its tributaries, much of it in the form of snow.
“This breaks new ground,” said Eric Kuhn, executive director of the Colorado River Water Conservation District, an agency based in Glenwood Springs. “Will it happen that way? We don’t know. But from a planning perspective, there is good information from these models.”
But it’s a still blurry picture of the future. Laurna Kaatz, a climate scientist with the Denver Water Department, said decisions involving multimillion-dollar water infrastructure should not be made based on the results so far.
“To say you’re going to plan for a single future based on one of the climate models with one emissions scenarios is, I don’t think, a responsible way of using the information,” she said.
In plotting the possible futures for 2040 to 2070, the climate scientists, hydrologists and water engineers examined 112 existing computer simulations of climate change. The simulations varied for many reasons, including uncertainty about the volume of greenhouse gases emissions during coming decades. Because of the complexity of atmospheric conditions that create what we call weather – and, over time, climate – these models have been unable to simulate the complex topography of mountainous areas that comprise the Colorado River headwaters. That topography, in turn, greatly influences precipitation.
Investigators in this study believe that downscaling techniques allowed them to get a better bead precipitation. While models have been clear about rising temperatures, until recently they swung broadly in precipitation. This study provides more definition, and the news for northern Colorado, where Colorado’s ski areas from Aspen to Steamboat and Winter Park are clustered, is not terrible. Winters will shorten, but plenty of snow will remain – if also drenched more often with rain.
“It doesn’t seem to indicate there’s a doomsday scenario for the ski industry or the fisheries of the upper Colorado River,” said Kuhn. “But it also means that while things are good for Summit and Grand counties, plus the upper Roaring Fork and Yampa (rivers), there’s still less water at Lee’s Ferry (Ariz.). And that means less water for Colorado to develop.”
Kuhn describes the study like a casino slot machine. While there is no certainty with any one pull, the odds favor the house. Similarly, the downscaling compilation of the computer simulations shows probability of a distinctly drier Colorado River Basin.
The dryness is the result of increased temperatures everywhere, although proportionately greater in lower elevations and in the more southerly areas. Crops such as corn and alfalfa will need more water. Winters will likely become shorter, runoff will occur earlier, and the hot, generally drier months of summer will last longer.
Effects suggested by the modeling vary by location. For example, temperatures by 2040 at the farming town of Delta, located in west-central Colorado, may rise 3.3 to 3.7 degrees Fahrenheit. Growing season will last 15 to 22 days longer. And crops will need 2.6 to 6.7 inches more of water per year. Ridgway Reservoir, which impounds snowmelt from the San Juan Mountains for use by farms, may start showing shorelines in June instead of July or August.
But even reservoirs located on drainages with increased winter precipitation may struggle to meet water demands. In effect, global warming will speed up the calendar by two or three weeks – and perhaps leave too little water for some farmers during late-season irrigation.
“When I saw these graphs, there was one word that came to my mind, and that was storage,” said Eric Wilkinson, who directs the Northern Colorado Water Conservancy District, at a public unveiling of the draft report in January.
Wilkinson’s agency diverts water from the Colorado River near Rocky Mountain National Park to cities along Colorado’s northern Front Range and to farms all the way to the Nebraska border. In other words, he sees the need for additional dams in discrete locations for use in years when more precipitation falls.
Gimbel similarly sees evidence for greater management. “Without some new storage projects in particular places, we won’t be able to use that water most efficiently,” she said. “It’s is definitely showing us it’s a time of limits, but we need to work more diligently on managing that water, so we can meet the needs within those limits.”
And that’s also the view from Glenn Porzak, who represents various water districts and ski companies along the I-70 corridor. “Storage is still the name of the game, and this will only accentuate the need for storage,” he says.
Kuhn sees the same glass half empty, and urges great caution in development of projects to tap the remaining resources.
The study also attempts to get a firmer thumb on how much water Colorado can develop under compacts that divies up water among the seven states in the Colorado River Basin. Lower-basin states – California, Nevada, and Arizona – long ago developed their apportionments.
But Colorado long believed it still has rights to retain addition water for cities, farms and other uses. Just how much has been disputed. Kuhn, for example, estimates a maximum of 150,000 acre-feet. More liberal estimates ran up to 1.4 million acre-feet. This study reports a range of zero to one million acre-feet.
All water officials and scientists agree this and other studies attempting to paint possible effects of global climate change on the American West are hardly the last word. “We will have to recognize that 20 years from now we will know a lot more than we know now,” said Kuhn.
The study, still in draft form, is now available for a 90-day public review. It can be found at http://cwcb.state.co.us/.
Colorado state officials also plan a second major investigation, which Gimbel characterizes as a “what-if type” of study. The study will attempt to get a better handle on Colorado’s water story if existing conditional rights – those filed but not yet executed – are perfected.
One major what-if is whether Aaron Million, the Fort Collins-based entrepreneur, is successful in getting rights to develop major quantities of water from the Green River, a tributary to the Colorado, at or near the Flaming Gorge Reservoir on the Utah-border. The question is whet that would mean for water availability in other parts of Colorado, including the Western Slope.
That second study was originally slated to begin immediately, but may be delayed because of the state’s declining revenues.
Parallel to and somewhat overlapping the Colorado River Water Availability Study is one commissioned by the Front Range Water Users Alliance. This second study takes a more narrow look at the headwaters on both sides of the Continental Divide, including rivers located near the ski towns of Winter Park, Breckenridge, Vail, and Aspen, which are all tapped by Front Range cities.