Signs of more drought ahead for Colorado River basin

National Oceanic and Atmospheric Administration map of drought conditions

Runoff levels in the Colorado River from melting snowpack peaked early last week, the earliest peak in the past 50 years. It's also the fourth lowest volume of peak runoff recorded in 85 years. Peak runoff's early appearance and modest height predict a drought that experts say will be more common, Allen Best reports for Route Fifty.

Several parts of the U.S. already face drought conditions, mainly the Southwest. That will likely hurt the nearly 40 million people and 5 million acres of farmland that depend on the Colorado and its tributaries.

"If you ask why there is so little runoff in the Colorado and other rivers this year and why it has come so early, the No. 1 reason is we didn’t get much snowfall. That explains the bulk of this anomaly,"  Jeff Lukas, a research integration specialist with the University of Colorado’s Western Water Assessment, told Best. "But the temperature, much warmer than normal, especially from November to January, is a part of the story."

Lukas noted that runoffs have been unusually low for the past 16 years and that droughts are now more common than they were in the past, which he said "may speak to the contribution of human-caused warming."

Increased temperature is the main cause of the drought, with precipitation a secondary contributor, according to a 2017 paper by Jonathan Overpeck, dean of the School for Environment and Sustainability at the University of Michigan. "Temperatures in the region have increased, and as they do, the warming atmosphere needs more moisture.," Best reports. "Overpeck and his co-researcher, Brad Udall of Colorado State University, concluded that the moisture is being induced into the atmosphere through increased evaporation and transpiration." 

"This turns out to be the very biggest consequence of the temperature-induced drought in the Colorado River Basin,” Overpeck said. "Wildfire is going crazy in the Southwest, and it’s for the same reason."