New Research Highlights Growing Threat of Consecutive Wildfires and Heavy Rain in the West
A study published in Science Advances on April 3, 2022, warns that the western United States will experience a sharp rise in the sequence of wildfires followed by intense downpours that trigger floods and mudslides. Under a worst‑case climate‑change scenario, the combined fire‑flood hazard could become eight times more common in the Pacific Northwest, twice as likely in California, and about 50 % more frequent in Colorado by the year 2100. The research examined 11 western states, paying particular attention to four where the projected increase is strongest: California, Oregon, Washington, and Colorado.
It focused on how human‑driven warming intensifies the link between extreme fire events and subsequent heavy rainfall. The analysis shows that roughly 90 % of extreme fire incidents will be followed by at least three extraordinary downpours in the same spot within five years.
This pattern emerges because, while the region overall becomes drier and the fire season lengthens, bursts of intense rain are growing stronger and arriving earlier in the calendar year. Consequently, landscapes can be struck by both hazards in quick succession. Study co‑author Samantha Stevenson, a climate scientist at the University of California Santa Barbara, explained, “One disaster is bad.
Two disasters in rapid succession are even worse because you’re already reeling from the first one.” She added, “But in the particular case of wildfire plus extreme rain, the wildfire is setting you up for worse consequences because you’re losing your vegetation, you’re changing soil properties and making that landscape more conducive to destructive flooding.” She pointed to the Thomas Fire, which ignited in late 2017 in Southern California. Roughly a month later, a downpour delivering half an inch of rain in just five minutes triggered mudslides in Montecito that claimed 23 lives.
Stevenson recalled, “Oh yeah, it was crazy. Like the entire highway was blocked off with like a wall of mud. There were boulders in people’s living rooms.” Co‑author Daniel Swain, a western weather expert at UCLA who resides in Colorado, noted that he had to evacuate his Boulder home due to a fire the week before the study’s release.
The publication date coincided with the onset of the flash‑flood season in that area. Swain observed that, especially in the Pacific Northwest, fire and flood seasons are lengthening and converging.
He warned that while both hazards will intensify, extreme rainfall is projected to increase more sharply, creating “a double whammy, a situation where you have the candle burning at both ends.” He added that it is “entirely foreseeable that some of these places will literally still have fires burning when the first extreme rainfall event extinguishes them.” The authors cautioned that the worst‑case warming pathway they used—based on dozens of large‑scale climate model simulations—is becoming less probable as many nations, including the United States and Europe, cut heat‑trapping emissions.
Lead author Danielle Touma of the National Center for Atmospheric Research said that, at the time of the study, simulations of more realistic moderate‑emission scenarios were not available. Nevertheless, she noted that under such moderate pathways the Pacific Northwest would likely still see a four‑fold rise in fire‑flood events.
