Shorter winters, hotter summers

Colorado’s Western Slope at mid-century will become hotter. Crops such as corn and alfalfa will need more water. Winters will likely become shorter, runoff will occur earlier in the year, and the hot, generally drier months of summer will last longer.

But the Colorado River Water Availability Study foresees less uniformity for winter precipitation: much less snow south of Interstate 70, but increased snowfall and winter rain in the Meeker, Steamboat Springs and Grand Lake areas.

The $1 million study, which was released this week in draft form, is described by Colorado water officials 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.

The Colorado River Water Availability Study downscales information found in global circulation models in an effort to better understand the range of possibilities that will result form greenhouse gas emissions accumulating in the atmosphere.

“This breaks new ground,” says Eric Kuhn, general manager of the Colorado River Water Conservation District. “Will it happen that way? We don’t know. But from a planning perspective, there is good information from these models.”

Kuhn explains that much as a casino slot machine has odds favoring the casino, the statistical compilation clearly shows the probabilities of a distinctly drier Colorado River Basin in the years 2040 and 2070. He maintains that given this probability, Colorado should develop its remaining water resources very cautiously, if at all.

But Eric Wilkinson, who manages the Northern Colorado Water Conservancy District, offered a different bottom-line at a January meeting. “When I saw these graphs, there was one word that came to my mind, and that was storage,” he said. He foresees more dams and reservoirs. The study finds that earlier runoff and more rare big water users will likely resulting in existing reservoirs being unable to meet needs of farms and cities in late summer and fall.

But climate scientists and water officials both agree that this future remains a blurry one. Laurna Kaatz, a climate scientist with the Denver Water Department, said decisions involving multimillion dollar water infrastructure should nto 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 says.

Precise effects vary by location. For example, temperatures by 2040 at the farming town of Delta, locate 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. And Ridgway Reservoir, which impounds snowmelt from the San Juan Mountains, may start showing shorelines in June instead of July or August.

The draft study is expected to be released within the next few weeks for a formal 90-day public review. A parallel study commissioned by the Front Range Water User Alliance more narrowly examines effect of the changing climate on headwaters on both sides of the Continental Divide that are tapped by Denver, Colorado Springs, Pueblo and other Front Range cities and districts.

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