Fire speed, not size, poses a greater threat to people and infrastructure.
A recent study by the University of Colorado Boulder found that fast-growing fires caused nearly 90 percent of fire-related damages in the United States from 2001 to 2020, even though such fires are quite uncommon. “Fast fires” can send embers airborne, igniting homes before emergency services can respond. The research, published today in Science, indicates that these fires are becoming quicker in the Western U.S., raising the danger for millions.
This study reveals a significant gap in fire hazard preparedness across the U.S.—current national fire risk evaluations do not consider fire speed, nor do they offer guidance on how communities can enhance their readiness for rapid fire growth.
“People talk a lot about megafires because of their size, but to better protect our homes and communities, we must understand and prepare for how quickly fires can spread,” stated Jennifer Balch, CIRES fellow, associate professor of Geography, and the study’s lead author. “Fire speed is more significant for safeguarding lives.”
Balch and her team decided to investigate fire speed more closely after the Marshall Fire devastated over 1,000 homes in Boulder County, Colorado, in December 2021. Although it consumed less than 6,100 acres (24.7 square kilometers), it escalated rapidly due to dry conditions and strong winds. Within just an hour of being reported, it reached a town three miles (4.8 kilometers) away, leading to the evacuation of tens of thousands. This event motivated Balch’s team to explore how quickly fires can grow and what that means for fire risk nationwide.
The researchers analyzed satellite data of over 60,000 fires in the contiguous U.S. between 2001 and 2020. By using an advanced algorithm to process data from each satellite pixel, they tracked and documented the perimeter of each fire on a daily basis.
“Previously, we only had fragmented data regarding fire speed,” mentioned Virginia Iglesias, interim director of Earth Lab and co-author of the study. “We utilized Earth observations and remote sensing data to systematically study fire growth across the country.”
Using the fire perimeter maps, the team calculated the rate at which each fire expanded. They particularly focused on the fastest fires, which grew over 4,003 acres (16.2 square kilometers) in just one day, and examined how these peak growth rates changed over time. Their analysis showed that in the last twenty years, the average maximum growth rate of the fastest fires in the Western U.S. has surged by an astonishing 250 percent.
“In just a couple of decades, fires in the western U.S. have become quicker,” Balch noted. “We need to concentrate on preparing our communities through methods such as fortifying homes and creating thorough evacuation strategies.”
To understand the effects of rapid fires on people and infrastructure, the researchers compared the growth rates of the fastest fires to incident report data detailing the number of structures affected per fire. They discovered that fast fires accounted for 88 percent of homes destroyed from 2001 to 2020, even though they made up only 2.7 percent of total fire incidents. Fires that damaged or destroyed over 100 structures showed maximum growth rates exceeding 21,000 acres (85 square kilometers) in one day.
“These findings shift our perspective on wildfire risk, emphasizing growth rate as a critical factor in determining a fire’s potential for destruction,” Iglesias stated.
The study also points out a significant risk assessment deficiency. Current wildfire risk models at the national level consider factors such as area burned, intensity, severity, and occurrence probability, yet they overlook fire growth rate and speed measurements. As a result, government agencies and insurance companies using these models lack crucial information on how fires spread, information that could help homeowners better protect themselves and their communities. The authors argue this needs urgent attention.
“When it comes to protecting infrastructure and facilitating effective evacuations, a fire’s growth speed may indeed be more important than its size,” Iglesias concluded.
