Here’s a look at what we think we know about future water supplies in the Colorado River Basin according to the Colorado River Water Availability Study, from Allen Best writing for the Vail Daily. From the article:
A new $1 million study suggests snowier and rainier winters in the northern mountains and drier ones in the south by the mid-21st century. But everywhere across the Western Slope, summers will be hotter, longer and drier, putting more stress on reservoirs. 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…
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 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 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,” 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, 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…
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/.
