New Colorado River drought discovery shows how bad things can get

A new study out Thursday sheds new light on the drought history of the Colorado River Basin, and only adds to current concerns about the ongoing Southwest megadrought.

Driving the news: Based on tree-ring records of historical streamflow in the Upper Colorado River Basin, the study uncovered a drought in the second century that was more severe than the ongoing 22-year region-wide drought event.

• The recently discovered 24-year drought between 129-150 CE likely ranks as the most severe drought in the past 2,000 years for this region, the study finds.

Why it matters: The newly found drought stands as an example of how much worse things can get, driven by natural climate fluctuations alone. If such a drought were to occur today, it would undoubtedly be even worse, researchers told Axios, due to the added effects of human-driven climate change.

• In addition, the results would be catastrophic, given the demand for water and energy in the booming Southwest.

The big picture: Right now, the entire West is experiencing drought conditions, not just part of the Colorado River Basin. Ninety-percent of New Mexico is in the two worst drought categories, and 60% of California and 55% of Nevada are in the same situation, for example. All of each of these states are in some form of drought as of this week.

• California just had its driest first five months of a year on record, raising fears about the upcoming wildfire season.
• Benjamin Cook, a NASA drought researcher whose work has helped distinguish the ongoing megadrought through history, said the widespread nature of the current drought is one of the strongest pieces of evidence pointing to the role human-caused climate change is playing in it, Cook said. It also distinguishes the current event from the drought identified in the study.
• "Climate change is making it warmer pretty much everywhere, which increases evaporation and enhances surface drying over a broad geographic region," Cook told Axios via email.
• "You can easily find localized droughts in the past that exceed the intensity of the current drought. But no other drought in the last 1200 years really matches the combination of intensity and spatial extent of the ongoing megadrought."

How they did it: For the new study, published in Geophysical Research Letters, scientists examined streamgage records at the Lees Ferry gage in Arizona and combined it with statistical reconstructions of drought history dating to the year 1 CE, based on tree ring analyses.

• Tree rings can reveal past drought events as well as periods with abundant rainfall.

What they're saying: "We know that warmer temperatures worsen the impacts of drought," study coauthor Connie Woodhouse of the University of Arizona told Axios via email. "There is good chance that if a 2nd-century-type drought occurred in the future, its impacts would be worsened because of the warmer temperatures."

• Both Woodhouse and Cook also noted that droughts tend to be self-reinforcing, which is something both are concerned about this summer. "A hot dry summer leads to soil moisture deficits which we now know have a significant impact on how much of next year's winter snowpack runs off into the river, and how much goes towards replenishing dry soils," Woodhouse said.