The Colorado River Basin, like much of the southwestern U.S., is experiencing a drought so historic—it began in 1999—that it’s been called a megadrought. In the basin, whose river provides water to seven states and Mexico, that drought is the product of warming temperatures and reduced precipitation, especially in the form of winter snow.

While the warming trend has been conclusively linked to the human activities driving climate change, the cause of the waning precipitation wasn’t as clear. Now, however, Jonathan Overpeck of the University of Michigan and Brad Udall of the Colorado Water Center at Colorado State University are convinced that anthropogenic climate change is the culprit as well.

“The drought’s been going on for over 25 years and there’s been a real downward trend in precipitation. But, even as recently as a year ago, we thought that just might be part of the natural variability—we figured the precipitation might turn around,” said Overpeck, the dean of the U-M School for Environment and Sustainability. “Within the last year, there’s been research that tells us pretty convincingly that’s not the case. Longterm, there are going to be more dry winters than wet winters and that’s due to climate change.”

Starting with a cornerstone 2017 study, Udall and Overpeck have been detailing the state of the drought and its climate drivers with a series of graphs that use the best data and science available. In this year’s update to the graphs, published as part of a larger annual report just released by the Colorado River Research Group, the duo came to two conclusions. One, the downward precipitation trend is also due to human activity and, two, it’s unlikely to rebound until we do something about it.

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Read the full press release on the Michigan News website.