Key Colorado River basins could be at a tipping point: Study

Six key watersheds along the Colorado River have become increasingly vulnerable to drought and could be nearing a point of no return, a new study has found.

These basins, located in Colorado's "Western Slope" region — the part of the state west of the Continental Divide — face a critical situation in which traditional water delivery capabilities may no longer be available, according to the study, published in Earth's Future.

The six watersheds collectively support a $5 billion annual agricultural economy and also feed the Lake Powell reservoir — the second largest reservoir in the Colorado River region.

"Water supplies in the West Slope Basins could be near a tipping point if a dryer future is realized," the study authors wrote.

"A relatively modest decrease in streamflow could generate a cascade of multi-sectoral impacts, threatening agricultural output, lowering reservoir levels, and harming sensitive ecosystems," they added.

The researchers — from Cornell University and Utrecht University in the Netherlands — paired the Colorado river's current planning model with a new modeling framework that created hundreds of thousands of streamflow scenarios, under historical and climate-change conditions.

Their results raised concerns by indicating that vulnerability analyses that rely only on historical records might be severely underestimating the potential impacts of drought events.

“Our work shows that even relatively middle-of-the-road climate change and streamflow declines in these basins flows can threaten to put the system at risk of breaching a tipping point," senior author Patrick Reed, a professor at Cornell's School of Civil and Environmental Engineering, said in a statement.

At such a point, Reed explained, the basins might become unable "to maintain the levels of deliveries to Lake Powell that we’re accustomed to over recent history."

For example, the authors cited a 2021 drought that led Lake Powell to drop to unprecedented lows, prompting the federal Bureau of Reclamation to declare the first-ever water shortage for the upper portion of the Colorado River Basin.

Such shortages, according to the study, can emerge from the combination of a basin's internal variability and the impacts of drought on the region as a whole.

The authors said that their research was designed to help better understand the limits of current management policies, while clarifying where new sustainable management strategies could be useful.

Their findings, they explained, are particularly timely, as the seven Colorado River states and federal agencies continue to negotiate long-term water-sharing agreements for the basin's future.