ST. GEORGE — Warming temperatures are causing diminishing flows for the Colorado River, according to a new study published Thursday.
The report, authored by Paul Milly and Krista Dunne of the U.S. Geological Survey and published in Science, suggests that climate change could lead to a 20% to 30% decrease in the river’s flow by the middle of the century.
The analysis comes in the midst of Utah’s latest effort to develop the Lake Powell Pipeline. The project would transport water from the reservoir to serve as a second water source for the fast-growing communities in the southwest corner of the state. For over a decade, Utah lawmakers have pushed the pipeline, which is currently under review by the Bureau of Reclamation.
The study builds on a growing body of research that shows the relationship between higher temperatures and less water in the Colorado River Basin, said Brad Udall, a senior water and climate researcher at Colorado State University.
“That means that any new diversion in the river and any existing diversions are going to have to figure out how to use less water,” he said. “What’s particularly concerning to me about the Lake Powell Pipeline is that the way the Colorado River Compact works is that Johnny Come Lately diversions put the whole system at risk.”
Udall was referring to the 1922 agreement — often called “The Law of the River” — that divides the river’s flow between the upper-basin states of Colorado, New Mexico, Utah and Wyoming and the lower-basin states of Nevada, Arizona and California.
The risk Udall warned of is a scenario in which water levels across the basin drop so low that the upper-basin states are not able to deliver the agreed upon amount to the lower basin. This would trigger the first-ever “compact call” and result in unprecedented reductions across the entire system.
“How one would address the equities of this no one knows. How one would actually implement this no one knows,” he said. “So that’s the great unknown that makes people very nervous.”
Utah has long argued it is only using a fraction of the water afforded to it under the compact. And local water officials like Zachary Renstrom, deputy general manager of the Washington County Water Conservancy District, say that climate change is why they need the project now.
He says that his county — which is projected to triple in population by 2065 — depends solely on the Virgin River, which is even more vulnerable to climate change.
“Having a community based upon one small desert tributary of the Colorado River makes me extremely worried,” he said.
Conservancy district officials acknowledge that climate change is affecting the Colorado River basin. But they contend that the river is still the most reliable source of water available and has sufficient water for the project, according to models created by the Bureau of Reclamation.
The bureau became the lead agency reviewing the project in October, after Utah withdrew its application from the Federal Energy Regulatory Commission. It is currently preparing a draft environmental impact statement for the pipeline, which is scheduled for release this summer.
Project manager Rick Baxter told KUER that the statement will address potential impacts of climate change.
Correction 2/21/20 1:09 p.m. MT: A previous version of this story misstated Brad Udall's university.
Clarification 2/28/20 5:59 p.m. MT: This story was changed to clarify that the Lake Powell Pipeline would create a second source of culinary water in Southwest Utah.