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Wildland fringes are the areas with the fastest population growth in West. These ecosystems are most at risk from wildfires.
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Wildland fringes are the areas with the fastest population growth in West. These ecosystems are most at risk from wildfires.

Illustration showing how drier plants lead to more fire.


The view from the foothills of the Sierra Nevada in Southern California can be beautiful – pine forests and chaparral spill across an often rugged landscape. But as more people build homes in this area, where development gets into wild land, they’re facing some of the highest risks for wildfires in the country.

The likelihood of an area being burned will depend on the type of trees, grasses, and plants present. However, our new research shows that some areas of the wildland-urban interface – the land where development ends and wilderness begins – are at much higher risk of burning than others. One reason is how vulnerable local vegetation is to drying in a warming climate.

In a Study published February 7, 2022Our team of climate scientists, fire scientist, and eco-hydrologists created a map that showed where vegetation is creating the most fire risks in the western U.S., and then compared it to where people have been moving into the wildland/urban interface.

Surprised to find that the areas with the greatest fire risk have the highest population growth rates. This includes areas in California and Washington as well as Texas.

The fires are influenced in large part by the sensitivity of plants

When a fire does break out, the amount of area that burns increases significantly if a region’s vegetation is drought sensitive, meaning it dries up easily after periods of little rainfall and hot temperatures.

Illustration showing how drier plants lead to more fire.

Depending on how sensitive the trees to drought, the same amount of dryness may cause different amounts of burned areas.
Krishna Rao, CC BY ND

Some vegetation loses moisture faster in dry conditions, just as a succulent is more resilient to water shortages than, for example, a citrus. Wildfires can be affected by a variety of sensitivity. We found that burned area increases by twice the amount in areas with the highest drought-like conditions. So fire hazard in areas such as central Arizona, eastern Oregon and southern California has outstripped the national average. But what about human vulnerability to wildfires?

Boom in wildland-urban population interface

Our research showed that, while the number of people who live in the wildland/urban interface increased by roughly twofold between 1990 and 2010, the population living in the highest-hazard areas grew by 160%. The potential for fires to start increases as more people move into these areas. risesAs does the number of people at-risk.

All in all, the population in high-hazard zones grew from 1,000,000 in 1990 to 2.65 million in 2010, the most recent year with population data. That’s an increase equivalent to the current populations of San Francisco and Seattle combined.

People still live in low-hazard areas of the wildland/urban interface. While the population grew by 107% from 5 million in 1990, to 10.4million in 2010, the growth in high-hazard areas has been much faster.

We don’t know what is causing the population boom in these highly sensitive areas of the western U.S. Building codes, People who are timber-dependent and those looking for homes surrounded with forests may have contributed to the expansion of the wildland-urban interface, but those factors alone don’t explain why population would rise the most in the most vulnerable regions.

However, a map of vegetation’s sensitivity to water shortages can provide some insight. You can link Satellite-based estimates of dryness in vegetationBased on climate observations, we were able to create maps at the continental level of vegetation moisture. We now know where the most fire-prone and drought-vulnerable vegetation is located for the first time.

The map shows how the Sierra Nevada, San Diego, San Diego and San Antonio foothills are all drought-sensitive areas. This has led to increased population growth in the wildland/urban interface.

Map of the U.S. West showing high-risk areas in Texas and California that also have high population growth.
High-risk areas are shown on a map showing vegetation sensitivity to droughts (pink), and the expansion of wildland-urban interface (black) between 1990 and 2010. Missing satellite data is what causes the white streak.
Krishna Rao, CC BY ND

Further research on the demographics and land use in these areas can shed light into the driving factors of growth. For example, the Bay Area has seen a shortage of affordable housing. Further from cities and may be encouraging more development in the wildland-urban interface, including high-risk areas that hadn’t previously been developed.

What can people who live in high-risk areas do to help themselves?

The disproportionate population growth in high-hazard areas is a warning that the likelihood of humans sparking a fire in an area with high-risk vegetation is rising – and that it may be higher than was previously understood.

Community leaders can use this information to identify areas where human activities overlap with drought-sensitive zones to improve land-use planning, prepare firefighting equipment, and create safer evacuation routes.

Property owners can keep a safe defensible spaceTo help protect their structures from wildfires, ensure that there is at least 100 feet of non-vegetated land along the sides of any home. RetrofittingHomes with double-paned windows or fire-retarding material can also help.

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These preventive measures can reduce the likelihood of an accident. Wildfires can cause huge lossesAll inclusive Wildfire smoke can cause severe air quality problemsThis allows humans to coexist more safely with natural fires.

Preparing homes for wildfires can take months, so it’s important to use the winter, when many of these areas have their wet seasons, to be ready by the time the land dries out and wildfires ramp up in spring.


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