From The St. George Spectrum (Lexi Peery):
Climate change is increasing the variability of the Colorado River so much so that the river could lose one-fourth of its flow by 2050, according to a new government study.
As plans for the 140-mile Lake Powell Pipeline — which would divert over 86,000 acre-feet annually from the reservoir to southwestern Utah — are under review by the Bureau of Reclamation, what does the Colorado River’s diminishing flows mean for the project?
The new report, produced by the U.S. Geological Survey and published in Science, attributes a 16% decline in the river’s flow from 2000-2017 to rising temperatures. The Colorado River hydrates seven downstream states, storing water in shrinking Lake Powell and Lake Mead reservoirs.
Washington County Water Conservancy District Manager Zach Renstrom said he thinks the variability of climate change provides even more reason for the county to pursue the pipeline.
“Climate change is a big deal to us, we are very concerned about it, and specifically how it’s going to affect our watershed,” Renstrom said. “When we look at these dynamics, they’re one of the strong arguments for the Lake Powell Pipeline because we need to make sure to have a robust infrastructure in place so we can adjust for (climate change).”
Rising temperatures, less snow
USGS scientists considered two scenarios of climate change in the Colorado River study. In one, warmer temperatures by 2050 would reduce the amount of water flowing in the river by 14-26%. In the other scenario, warming would take away 19-31% of the river’s flow…
Milly and fellow USGS scientist Krista Dunne focused on the reflectivity of snow, known as albedo, as a key element in the river’s sensitivity to warming. They zeroed in on the role of snow cover as a “protective shield” for water in the river basin.
Milly likened the flowing river to the leftovers of the “meal” of snow and rain that falls across the basin after evaporation has “eaten” its share…
And the amount consumed by evaporation is driven by how much energy the basin absorbs in the form of sunlight. The snow cover in the Rocky Mountains reflects back to the sky and space a significant fraction of the sunlight.
As the world gets hotter with the burning of fossil fuels, more of the precipitation falls as rain instead of snow. And the snow melts away earlier in the year. As the snow cover in the mountains is progressively lost, the river basin absorbs more energy…
“When we talk about structural deficits and overuse of the Colorado River system, it’s exclusive to the lower basin,” WCWCD spokesperson Karry Rathje said.
Washington County’s population is projected to grow 229% by 2050, but Renstrom says he’s worried that growth may come sooner than expected. He’s pushing to get the pipeline going in the next 10 years in order to diversify the county’s water supply.
“Even when we look at reduced flows … the water in the Lake Powell Pipeline should be available for us to withdraw,” Renstrom said. “As the guy who has to worry about where water is coming from in 30 years if some of the higher-end climate models come to pass, and the Virgin River is dried up, it makes me feel very secure that we’ll have another tool in that toolbox.”