A fiery forecast
Longer, hotter summers predicted for Western Slope

A Durango crew floats through Cataract Canyon last spring. According to the newly released draft Colorado River Water Availability Study, Western Slope summers are expected to be hotter, longer and drier and will put more stress on the region’s water resources. The $1 million study has been described as “cutting edge” by state water officials and has them scrambling for ways to preserve the state’s precious resource. /Photo by Stephen Eginoire

by Allen Best

Global warming will raise temperatures in Colorado, right? But will it also get drier? It depends on who you ask. A new $1 million study suggests snowier and rainier winters in the northern mountains and drier ones in the state’s south by the mid-21st century. And everywhere across the Western Slope, summers are expected to be hotter, longer and drier, putting more stress on reservoirs.

These tentative conclusions are found in the newly released draft Colorado River Water Availability Study, a $1 million effort described as “cutting edge” by state water officials, who commissioned it.

“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 water. About three-quarters of the state’s water, much of it in the form of snow, originates west of the Continental Divide, in the headwaters of the Colorado River.

“This breaks new ground,” said Eric Kuhn, executive director of the Colorado River Water Conservation District, 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 blurry picture of the future at best. Laurna Kaatz, a climate scientist with the Denver Water Department, said decisions involving multimillion-dollar water infrastructure should not be 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 possibilities for 2040-70, the climate scientists, hydrologists and water engineers examined 112 computer simulations of climate change. The simulations were based on varying amounts of greenhouse gas emissions during coming decades.

Investigators in this study believe that downscaling techniques allowed them to get a better bead on 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 many of Colorado’s ski areas are clustered, is not terrible. Winters will shorten, but plenty of snow will remain, albeit 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,” says 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, downscaling 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 at the farming town of Delta may rise as much as 3.7 degrees Fahrenheit by 2040. The growing season will last 15 to 22 days longer, but crops will need 2.6 - 6.7 inches more of water per year. Ridgway Reservoir, which impounds snowmelt from the San Juan Mountains, may start showing shorelines in June instead of July or August.

But even reservoirs in areas with increased winter precipitation may struggle to meet demands. In effect, global warming will speed up the calendar by two or three weeks – and perhaps leave too little water for late-season irrigation.

“When I saw these graphs, there was one word that came to mind, and that was ‘storage,’” said Eric Wilkinson, director the Northern Colorado Water Conservancy District, at a public meeting on the report in January.

Wilkerson’s agency diverts water from the Colorado River near Rocky Mountain National Park to cities along the northern Front Range and farms all the way to the Nebraska border. In other words, he sees the need for additional dams in years when more precipitation falls.

Gimbel, of the Colorado Water Conservation Board, also sees evidence for greater management. “Without some new storage projects, we won’t be able to use that water most efficiently,” she says. “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.”

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,” he says.

The study also attempts to get a firmer grasp on how much water Colorado can develop under compacts that divvy 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 believes it still has rights to retain addition water. Just how much has been disputed. Kuhn estimates a maximum of 150,000 acre-feet. More liberal estimates run up to more than a million acre-feet. This study assumes a range of zero to 400,000 acre-feet.

One thing all the water officials and scientists agree on is that this and other studies attempting to paint possible effects of climate change 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.

State officials also plan a second major investigation, which Gimbel characterizes as a “what-if” study. The study will attempt to get a better handle on existing conditional rights – those filed but not yet executed. One major “what-if” is whether Aaron Million, a Fort Collins entrepreneur, is successful in getting rights to develop major quantities of water from the Green River at or near the Flaming Gorge Reservoir on the Utah border.

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 done by the Front Range Water Users Alliance. This one takes a more narrow look at the headwaters on both sides of the Continental Divide, particularly those near Winter Park, Breckenridge, Vail and Aspen, which are all tapped by Front Range cities.

Meanwhile, the Bureau of Reclamation is launching a more detailed and broader look at how a warming climate may impact the reservoirs it administers along the Colorado River and its tributaries. •

The Colorado River Water Availability Study is now available for public review at: http://cwcb.state.co.us/WaterInfo/CRWAS/