The Dixie Fire in California was the largest wildfire of 2021 in the U.S. It burned from July to October, consuming 963,309 acres and destroying 1,329 structures, 600 of which were homes. The Dixie Fire was the largest single wildfire in California history, but not the largest overall. That honor goes to the August Complex Fire, so named because on August 30, 2020, four fires burned together to create one massive wildfire that consumed 1,032,648 acres—an area larger than the state of Rhode Island. One person died in each of these fires. Yet, despite their vast sizes, these fires pale in terms of death and destruction compared with California’s 2018 Camp Fire, which killed 85 people and destroyed 18,804 buildings, or the Tubbs fire of 2017, which killed 22 people and destroyed 5,636 buildings. And this is only in the state of California. Though the largest and deadliest U.S. fires in the last decade have all occurred there, notable fires have broken out in Washington (Carlton Complex Fire), Arizona (Yarnell Hill Fire), and New Mexico and Arizona (Wallow Fire). During 2020 alone, over 13 million acres were consumed, and nearly 15,000 buildings were destroyed in the U.S. by “large event” wildfires (those that burn more than 1,000 acres).

While none of these are the most destructive in U.S. history (compare to The Big Burn of 1910, a single fire that killed 87 people and consumed 3 million acres in the Northern Rockies in August 1910, or the 1871 Peshtigo Fire, which killed 2,500 people and burned 1.2 million acres in Wisconsin and Northern Michigan), the incidence of wildfire has increased exponentially in recent history. Though there is debate over whether the overall number of wildfires has increased, there is little debate that the intensity of, the area consumed by, and the cost of reconstruction from wildfires have grown. According to NASA, which tracks wildfire activity by satellite, the average annual number of acres burned has been steadily increasing since 1950, and the number of “megafires” (fires that burn more than 100,000 acres) has increased in the past two decades.

All of this has deeply influenced wildfire safety policy in the U.S. Traditionally, the recommendation to protect homes was to create “defensible space”—an area of landscaping with little combustible material surrounding a home—so fires would not have a chance to reach the building. (Note: The specific zones that define “defensible space” around a home vary. The The interactive graphic, “Hardening Structures Against Wildfires,” shown below in the article details the three zones that are commonly recommended mostly outside California. The California Building Code has a more stringent definition that includes a zone clear of combustible material that extends 30 feet around the house, an area of low, clumped vegetation extending from 30 to 70 feet, and a reduced fuel area from 70 feet to the property boundary. These stricter requirements have also been adopted outside California, just not as frequently as those shown.)

While defensible space is still a primary strategy for protecting homes, it has proven less effective for two reasons: The first is the increase in the concentration of homes in developments. Smaller lot sizes mean homes often don’t have sufficient room to create much defensible space around them. Second, the increase in the intensity of wildfires has made blowing embers, which can travel distances measured in miles, a primary cause of ignition for building fires. These days, the prime strategy involves the hardening of homes to resist damages.

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