extreme weather

How is drought affected by climate change?

One significant impact of climate change is drought—a lack of precipitation coupled with heat that speeds up evaporation and leaves the landscape primed for wildfire. Of course, drought has always made periodic appearances in the American West, but warming global temperatures associated with human-driven climate change is increasing the frequency and impacts of drought. This year, the West is struggling with a “megadrought,” defined as a drought lasting two decades or more.

Some scientific models suggest that climate change could bring more precipitation to the West. But, even if that were the case, the higher temperatures that climate models seem to agree on will also mean drier conditions, said Becky Bolinger, assistant state climatologist with the Colorado Climate Center at Colorado State University.

“When you’re adding on more heat, you’re probably evaporating more into the air and losing more moisture from the soils than what you would if the temperatures weren’t as hot,” she said, pointing to earlier snowmelt and more evaporation. “You’re still going to be at risk for drought, simply based on warmer temperatures.”

In the West, snowpack is more important for water availability and supply than rainfall events, Bolinger added. That’s because the frozen water in the mountains acts as a kind of freezer that allows the melting snow to gradually fill streams and reservoirs that humans, wildlife and the environment have evolved to rely on through the summer.

“You could get the same amount of snowpack as you’ve always gotten, but if you warm the temperatures, then when the snow melt time period begins in the spring, it could run off earlier and run off faster and more of it could be lost to evaporation,” she said, pointing out that that leaves less for water supplies struggling to recover between drought years. 

As heat wave after heat wave baked the West in 2021 during the region’s hottest June ever recorded, drought deepened and spread. By mid-July, nearly two thirds of the region was in extreme or exceptional drought, according to government data. And the nation’s two largest reservoirs, Lake Powell and Lake Mead, fell to near-record low levels and prompted leaders to cut water allocations to the 40 million people in seven states who rely on the lakes for water.

In addition, the dryness dug in, creating moisture deficits that, according to new research, go hand in hand with higher temperatures. Tinder-dry conditions meant an even greater risk of wildfire in a region that had already seen more than 1 million acres burned by wildfire.

“Evaporative demand and wildfire go hand in hand when you’re talking weather,” said Bolinger, whose state endured the largest two wildfires in its history last year. “If you have a hot day and a dry day, and then you add wind, you have really high evaporative demand and a higher risk for wildfires spreading out of control at the same time.”

—Judy Fahys

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