Over 40 million people from Los Angeles, California, to Denver, Colorado, are provided with water from the Colorado River. However, its flow has dwindled by 20% compared to the last century, and scientists blame climate change.
A study, conducted by US Geological Survey scientists Krista A. Dunne and Chris Milly, found that more than 50% of the decline in the river’s flow is associated with increasing temperatures. They warn that the risk of severe water shortages for the millions that depend on it is expected to grow as warming continues.
The scientists found that for every 1.8 degrees Fahrenheit of warming averaged across the river’s basin, its flow decreased by almost 10%. The region was already warmed by an average of 1.6 degrees Fahrenheit over the 20th and early 21st centuries.
The study, which was published in the journal Science, also analyzed the impact that action to reduce pollution of heat-trapping gases could have on the river’s water supply. Unfortunately, no matter what steps we take, it’s likely there will be some decrease in the flow. However, without cutting any emissions, the river’s discharge could potentially shrink anywhere between 19% and 31% by mid-century.
The vital Colorado River begins high in the Rocky Mountains of Wyoming and Colorado, then snakes down across the Southwest to the Gulf of California. According to Brad Udall, a senior climate scientist at Colorado State University, by the time the water arrives in California, its flow has reduced to a trickle. Udall has studied the Colorado River basin over the past thirty years.
As the river flows through the regions, water is diverted to supply major cities like Denver, Las Vegas, Los Angeles, and San Diego, as well as vegetable farms in Mexico and the US that feed billions around the globe. The researchers claim the river supports roughly $1 trillion of economic activity every year. “Without this river, American cities in the Southwest would dry up and blow away,” Udall added.
However, the scientists found that global warming is taking a significant toll on the snowpack that feeds the river its water. As hot temperatures rise, snow coverage declines, which means less water supply. Additionally, there was a severe drought that lasted two decades, leaving two main reservoirs, Lake Mead and Lake Powell, barely half full. That decline has since accelerated: both reservoirs hit record lows in August 2026, with Lake Powell falling to just 22% of its capacity. The same drying trend is starting to show up in household budgets, with research warning that climate change could double water bills in vulnerable cities.
Last year, the seven states that rely on the Colorado River signed a drought contingency plan that will govern the rights to it until 2026. Udall announced that negotiations would get started at the end of this year to determine how to distribute the water in a drier, more arid climate.
Udall said, “The science is crystal clear—we must reduce greenhouse gas emissions immediately. We now have the technologies, the policies, and favorable economics to accomplish greenhouse gas reductions. What we lack is the will.”
He clarifies that these findings only show that to save the river, we have to address the root of the problem, which is climate change, and we also need to gain more willpower.
