The wildland-urban interface of the West’s West is home to the fastest growth in population. It is these areas that are most vulnerable to wildfires that see the greatest population growth.

The view from the foothills of the Sierra Nevada in 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 that an area will burn will depend on what type of trees, plants, and grasses are 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. The main reason is how susceptible local vegetation to drying out in a warmer climate.

In a Published February 7, 2022 in a studyOur team of eco-hydrologists, fire scientists, and climate scientists mapped the areas where vegetation is causing the greatest fire risk in the western U.S. The map was then compared to the area where people have been moving into wildland-urban interface.

Surprised to find that the areas with the greatest fire risk have the fastest 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.

A succulent is more resilient to drought than a citrus tree. However, some vegetation loses water more quickly in dry conditions. Wildfires can be impacted by such sensitivity. We found that burned area in the most sensitive areas increases twice as fast as in the least sensitive. Fire hazard in California, central Arizona, and eastern Oregon has outpaced the average. But what about human exposure?

Boom in wildland and urban interface populations

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 its most-hazardous regions grew by 160%. These areas have more fire-prone areas as more people move in. risesThe number of people at high risk also increases.

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.

The wildland-urban interface has more people than ever, with a population that grew 107% from 5,000,000 in 1990 to 10.4M in 2010. However, the high-hazard zones have seen much faster growth.

We don’t know what is causing the population boom in these highly sensitive areas of the western U.S. Building codes, People looking for homes in forests and communities that are timber-dependent 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. By linking Satellite-based estimates of dryness in vegetationWe created maps of the vegetation moisture at continental scales using climate observations. We now know the exact locations of the most vulnerable and fire-prone vegetation.

The map shows how the Sierra Nevada, San Diego, San Diego, San Antonio, and the foothills of San Francisco Bay Area are all drought-sensitive areas. This map also shows how populations grew in the wildland/urban interface.

Further research that examines the demographics, local land use, and development regulations in these regions may shed light on the driving forces of growth in high-risk areas. For example, the Bay Area has seen a shortage of affordable housing. Cities are further away and may be encouraging more development in the wildland-urban interface, including high-risk areas that hadn’t previously been developed.

What can high-risk residents do?

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.

This knowledge can be used by community leaders to identify areas where human activity is incompatible with drought-sensitive regions. This will help to improve local land-use planning and prepare firefighting resources.

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.

These preventive measures can help to limit the incidence of cancer. Wildfires cause massive lossesIncludes Wildfire smoke causes severe damage to the air qualityThis 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.