How the Colorado River will Flow with Climate Change: Possibility of a 'Megadrought'

The Colorado River runs through the western United States, winding its way past major towns and cities. One of the longest rivers in the U.S., it provides water for more than 30 million people. Yet climate change may soon alter the course of this river. That's why in the past, scientists have tried to calculate exactly how much the river will be affected. Unfortunately, estimates ranged from a modest flow decrease of 6 percent by 2050 to a massive drop of 45 percent. Now, researchers have discovered exactly why these estimates for the Colorado River's flow range so widely.

In order to examine how a changing climate might affect the river, the researchers took several components into account. They looked at temperature, precipitation and challenges facing water managers. In addition, they looked at recent papers that estimate the future flow of the river, finding reasons for different estimates.

"We know, for example, that warmer temperatures will lead to more evaporation and less flow," said Bradley Udall, one of the researchers, in a news release. "Although projections of future precipitation aren't as clear, it's likely that we're going to see a reduction in overall flow in the Colorado."

There are several estimates for the Colorado River, which is the main issue. Yet this new research puts the studies in a single framework and identifies how they are all connected. More specifically, the researchers found that the estimates were affected by the climate models used, the models' spatial resolution and the representation of land surface hydrology.

The researchers didn't only examine the cause for the different estimates, though. They also highlighted several important realities faced by Western water managers that are reliant on Colorado River flows. The water is already overallocated; this means that if the flow lessens, it's likely that some areas may experience some major issues, such as severe droughts.

The river has actually experienced severe droughts in the past that were not affected by human-caused climate change. Found in tree ring records, it's likely that regions were dry and parched as the river's flow slowed to a crawl. Yet climate change could exacerbate drought, which could eventually lead to a "megadrought" that could result in decades of extremely low stream flow.

The findings have shown scientists exactly what affects estimates and could lead to better predictions in the future. This is crucial for understanding exactly how climate change might affect the Colorado River, and could allow officials to take precautions in order to mitigate impacts.

The findings are published in the journal Bulletin of the American Meteorological Society.