Study Warns of Growing Fire‑Flood Threat Across the Western United States
A new study published April 3 in Science Advances warns that the combination of extreme wildfire followed by intense rain could become far more common across the West as climate change progresses. Researchers examined eleven western states and found that, under a high‑emissions scenario, the fire‑flood “double punch” could increase eight‑fold in the Pacific Northwest, double in California, and rise about 50 percent in Colorado by the year 2100. Four of the states showed the strongest projected growth.
The authors link this trend to human‑caused climate change, which is making the region drier overall and lengthening the wildfire season while also producing more concentrated bursts of intense rain that arrive earlier in the year. When a fire strips vegetation and alters soil properties, the subsequent rain runs off bare slopes with little resistance, turning what would be ordinary rainfall into destructive debris flows and floods.
The study’s lead findings include a striking statistic: roughly 90 percent of extreme fire events will be followed by at least three extraordinary downpours in the same location within five years. This pattern is not a rare anomaly; it represents a emerging normal for communities that sit in burn scars. Samantha Stevenson, a climate scientist at the University of California, Santa Barbara and co‑author of the study, explained the danger of successive hazards.
“One disaster is bad. Two disasters in rapid succession are even worse because you’re already reeling from the first one,” she said.
“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.” To illustrate how the mechanism works, the paper points to the Thomas Fire that ignited in late 2017 in Southern California. About a month later, in January 2018, just half an inch of rain fell in five minutes over the burned hills above Montecito. The resulting mudslide killed 23 people.
The researchers note that this single event exemplifies the fire‑flood chain that the model predicts will become much more frequent. Looking ahead, the Pacific Northwest—a region that has not historically experienced catastrophic wildfires—could see the fire‑flood combination increase eight‑fold, meaning towns in Oregon and Washington that have never faced this pattern will need to prepare for it.
California, already coping with megafires and atmospheric rivers, would see the threat double. Colorado, where the 2021 Marshall Fire destroyed more than 1,000 structures, would experience roughly a 50 percent increase in such compound events. These projections have concrete implications for emergency planning. Fire season is increasingly bleeding into flood season, which may require redrawing evacuation zones, revising building codes to address both burn risk and debris‑flow risk, and updating insurance models to price for compound disasters rather than treating fire and flood as separate hazards.
The study concludes that the West will be hit harder and faster: fire arrives, then intense rain follows, the ground cannot hold the water, lives are lost, homes are swept away, and the same landscapes may burn again before they have recovered. As the authors put it, the numbers are not abstract; they describe a looming reality for millions of people living in the western United States.
