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New analysis examines state water needs
Colorado River study uses climate-change models to see future
Herald Denver Bureau
Its answer: It depends. But it's probably less water than the state needs.
At the bottom line, the Colorado River Water Availability Study projected somewhere between zero and 900,000 acre-feet a year left for Colorado.
That's a big spread, considering Colorado uses about 2.5 million acre-feet of water a year.
An acre-foot would cover a football field 12 inches deep and is a year's supply for about two suburban families.
Water experts said they knew the study would return a range of alternatives but are impressed because it is the first study to use global climate-change models to predict Colorado's water future in such a detailed way.
“They broke new ground. If you don't follow the science, they've done a lot of things that have never been done before," said Eric Kuhn, head of the Colorado River Water Conservation District.
Kuhn was one of the first Colorado water experts to warn that climate change could dry up western rivers.
The study's authors presented the results from the first phase to the Colorado Water Congress on Thursday.
They took global climate models and tried to refine them to a smaller geographic area in Western Colorado. In general, the Colorado model predicts warmer temperatures, wetter winters and drier summers, with more intense heat and dryness in Southern Colorado and at lower elevations.
Based on these numbers, the study projected how much water farmers would need for irrigation. The model ran hundreds of simulations and compared the results with current water use and the water available to Colorado under multistate agreements.
Legally, those agreements give Colorado 3.8 million acre-feet a year. But few people expect the state to get that much because if there's a shortage, the agreements require Arizona and California to get their full share before the upriver states can claim water.
“This study is very cutting-edge. The other states are very jealous of the fact that we've done so well," said Jennifer Gimbel, director of the Colorado Water Conservation Board, which coordinated the study.
The study's second phase will contemplate some “what-if" scenarios, Gimbel said.
Importantly, the first phase did not take into account oil shale or other future uses. Oil companies own massive conditional water rights on the Western Slope. The study so far has included only water rights currently in use.
A report on the first phase will be released in February. After that, the public will get two months to make comments, said Ben Harding, a contractor who helped do the study.
Water managers can use the study as they develop plans for the future, said Eric Wilkinson, head of the Northern Colorado Water Conservancy District.
Wilkinson took note of the prediction that reservoirs will be drawn down more often because warm temperatures will make peak river flows arrive earlier.
“Thank heaven for the storage we already have, and we better be looking at storage in the future," Wilkinson said.
Kuhn agreed the study will be useful in planning for the next several decades of Colorado's water system. He warned that water the state needs might not be there in the future.
“It's going to take probably 20 years to develop better science. Between now and then, there's an extremely large risk," Kuhn said.
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