To end the Colorado River Basin's megadrought, 'we just need to stop climate change,' U-M expert says. 'We know how to stop it and it's not too late to stop it.'
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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.
"Because we understand the cause of the decline in precipitation and the increase in temperature, we know how to stop it. We just have to stop climate change. No big deal, right?" Overpeck said. "But we know how to stop it, we have the solutions, and it's not too late to stop it."
The duo said that having an extra year of data helped reach these conclusions, but the key development was the publication of two new studies in the field of climate science. One study, led by Jeremy Klavans of the University of Colorado, Boulder, helped improve climate models used to study the region. The second study, led by Victoria Todd of the University of Texas at Austin, used paleoclimatology techniques to reveal trends in temperatures from thousands of years ago to provide critical context for the current scenario.
Taken together, this led Udall and Overpeck to issue a reality check as the title for their contribution to the annual Colorado River Basin report: "Think Natural Flows Will Rebound in the Colorado River Basin? Think Again." To comfortably provide adequate water for the basin, the natural flow of the Colorado River should be at 16.5 million acre-feet, roughly the volume of 8 million Olympic sized pools, Overpeck said. It is currently closer to 12 million acre-feet.
Both Udall and Overpeck stressed there is natural variability and there will be wetter winters and dryer winters year to year. Their findings point to the long-term outlook being dryer overall, however. That said, the near-term outlook isn't great either, Udall said.
"We've basically taken the buffer out of the system. We've burned through all this reservoir storage over the past 26 years and we're one dry winter away from having very serious water usage cuts being enforced in a way that has never occurred before," Udall said. "And this winter is not starting off on a good foot."
People often ask Udall what happens if we don't limit greenhouse gas emissions and the warming of the average global temperature to international targets, like those set by the Paris Agreement. This precarious situation is one of the answers. While farmers and water managers in the region are acutely aware of the stakes, he said, the climate-water connection is of global importance. Droughts are enabling more devastating wildfires, while storms are carrying more water leading to more dangerous floods.
"This supercharging of the hydrological cycle is the story of climate change, in my mind. Climate change is water change," Udall said. "We control our own destiny here, but we're not controlling it right now."
