Between nature and neighborhoods: Mapping the dynamics of the wildland-urban interface and growing wildfire threats

Photo Credit

Courtesy photo by Kari Greer.

Fire adapted communities near Waldo Canyon Fire. Fire adapted communities are knowledgeable, engaged communities where actions of residents and agencies in relation to infrastructure, buildings, landscaping and the surrounding ecosystem lessen the need for extensive protection actions and enable the communities to safely accept fire as part of the surrounding landscape. Because every community is unique, the steps and strategies they take to improve their wildfire resilience will vary from place to place. 

Across the United States, patterns of development and sprawl have changed dramatically over time. Where forests and farmland once stood, housing developments and suburban sprawl are popping up, many on the periphery of growing metropolitan areas. This area where human settlement mixes with and meets natural landscapes is referred to as the wildland-urban interface (WUI), and a group of researchers has just released their findings in a paper entitled “Rising wildfire risk to houses in the United States, especially in grasslands and shrublands” based on a study of trends over the past three decades spanning from 1990 to 2020.

The picture of WUI growth that greets researchers is one of unique challenges and opportunities for natural resource managers and planners. As of 2020, 9.4% of the continental United States land area falls within the WUI. Yet, 32% of all housing is found in this area, and over the past three decades WUI has expanded dramatically in area and number of houses. From 1990 to 2020, the US total WUI increased by 31% in area, and the number of total WUI houses increased by 46%, from 30 million to 44 million. Expanding WUI growth places more homes at risk to wildfire and also increases disturbance to forests.

“When the problems posed by increased WUI demand are described, the western United States immediately comes to mind due to the increasingly bad wildfire seasons we have witnessed,” explains Northern Research Station research scientist Miranda Mockrin, “however, the proportion of housing falling into WUI is high across much of the United States, especially within the Intermountain West, Northeast, and Southeast, where over 40% of housing is in the WUI.” Not all of these places are fireprone, but all of them are dealing with the challenges of disturbance—such as non-native pests and loss of forest cover. Mockrin is the second author on the WUI findings that were released on November 10, 2023. The USDA Forest Service has been a long-time collaborator and funder of this work.

Over the past few decades, concerns over wildfire danger have increased dramatically as more than 55,000 homes burned between 2010 and 2020 alone. Mockrin and her co-authors looked at a unique data set of building losses, collected with partners, and funded by the Joint Fire Science Program, to unravel the patterns related to wildfires and WUI growth. As a result, researchers discovered an important association between types of vegetation and wildfires.

“News coverage in the media underscores a perception that wildfires are predominantly forest fires,” says Mockrin. “Our findings show that grassland and shrubland fires comprised 64% of the total burned acreage, while forest fires accounted for 27.3%.” When accounting for destruction of buildings in wildfires, 63.7% were destroyed in grassland and shrubland fires compared to 33.1% in forest fires. This dataset encompasses fires from 2000 to 2013 and partners are now working to further expand this important resource with losses from the past decade.

Researchers also sought to understand how changing housing development has contributed to wildfire risks in the WUI. Over time, housing expansion and the growing footprint of wildfires have both contributed to more housing being exposed to wildfire. For wildfires that occurred in the 1990s, the number of houses within these wildfire perimeters more than doubled by 2010. Thus, even in areas that had previously been subject to devastating wildfires, subsequent housing growth still took place—suggesting that past fires do not act as a deterrent to movement to the WUI. Regardless of future growth, the 44.1 million existing houses in the WUI today in 2020 means that WUI wildfires will remain a major problem.

“Our results highlight the prevalence of WUI losses, across the United States,” reflects Mockrin. “In the most fireprone WUI areas, it is not a question of if but of when a wildfire will strike. However, we highlight opportunities for proactive, site-specific solutions to be proposed and carried out by homeowners, builders, community leaders, and public agencies. These include updated building standards, innovative land use planning, and vegetation mitigation on public and private lands.”

Educating the public at large is also a key part of any plans to mitigate wildfire risks amidst growing settlement in the WUI. Just as Smokey Bear began his message nearly 80 years ago of “only you can prevent wildfires,” this study’s findings suggest that all parties involved—from individuals to state and federal governments—must take a proactive role in coordinating efforts to limit loss of lives and homes.