Global warming is greatly increasing the risk that extreme wildfires in the American West are followed by heavy rainfall, a new study has found.
The study highlights the need for better preparations for hazards, like mudslides and flash floods, that can cause devastation long after the flames from severe blazes are out, according to the New York Times.
Researchers from the University of California, Santa Barbara; the University o
California, Los Angeles; the Nature Conservancy of California; and Washington State University contributed to the study that was published in Science Advances on April 1, 2022.
The researchers found that if society continues emitting heat-trapping greenhouse gases at a high rate, the number of times that an extreme fire event is likely to be followed within one year by an extreme rainfall event will increase by more than eight times in the Pacific Northwest by the end of the century. It will more than double in California.
To come up with this conclusion, the study authors, including scientists at the National Center for Atmospheric Research (NCAR), used advanced computer models of past and future climate, as well as an index of weather variables associated with wildfire risks to reach their results, reports Science Daily.
The research focused on three regions that include California, Colorado, and the Pacific Northwest. Overall, the research showed that more than 90 percent of extreme fire events in these three regions will be followed by at least three extreme rainfalls within five years.
The “one-two punch” is evident
This “one-two punch,” – extreme fire events followed by extreme rain and flooding events – has already been well documented in previous studies, However, the increased frequency of extreme rainfall-after-fire events came as a surprise to the research team.
“It’s very concerning, given the destruction that comes with these kinds of events,” said lead author Danielle Touma, who did much of the research at the University of California, Santa Barbara, before coming to NCAR.
“Clearly we need to understand the risks better, as this creates a major threat to people and infrastructure,” Touma added.
“Three months to half a year after a fire, before the soil and vegetation have had time to recover, “are the times when these events can be really risky,” Dr. Touma said.
The evidence is well documented
The western United States is particularly vulnerable to the combined effects of wildfire and extreme rainfall, experiencing both hazards on a consistent basis. In a recent case, debris flows in Glenwood Canyon, Colorado in July 2021 occurred following heavy rainfall over the areas burned by the Grizzly Creek Fire in 2020.
In January 2018, Montecito in southern California experienced debris flows after a short but intense storm occurred over the footprint of the December 2017 Thomas Fire, leading to 23 fatalities and $200 million in property damage.
Wildfires during last year’s record heatwave in the Pacific Northwest worsened the damage from intense downpours that came less than six months later. For example, with more than 1,600 fires burning nearly 8,700 square kilometers of land, 2021 turned out to be British Columbia, Canada’s third worse fire season on record.
The extreme wildfires in the Pacific Northwest were followed by equally extreme atmospheric river-driven events that produced extensive flooding, deaths, and the destruction of property
In conclusion, the study finds that by the end of the century, more than half of the days with extremely high wildfire risk in parts of the Pacific Northwest, Idaho, Nevada, and Utah could be followed by severe downpours within a year.
Western Colorado and most of the Pacific Northwest are also projected to see a jump in the chance of heavy rains within three months of dangerous fire conditions. In California, the wildfire season and the rainy season tend to be more separate during the year.
“Even by midcentury, some places are seeing a doubling or tripling” of risk, said Daniel L. Swain, a climate scientist at the University of California, Los Angeles, and another author of the study. “That’s not that far in the future, and that’s not that much more additional warming than we’ve already seen.”