Wildland-Urban Interface Growth in the U.S.

Wildland urban interface in the conterminous United States 2020. Map from Wildland-Urban Interface (WUI) Change 1990-2020 at University of Wisconsin-Madison SILVIS Lab.

Wildland-urban interface (WUI) areas – where houses and other development meet or mix with undeveloped natural areas – are places of transition and change. Undeveloped wildlands offer extensive opportunities for outdoor recreation and the aesthetic and personal advantages of living “in the country.” At the same time, human development changes wildlands over time, eating away at the edges, breaking large natural areas into smaller patches, and changing forest structure and composition. When housing expands in proximity to forest and rangelands, more houses and people are at risk of wildfire, and wildfire management becomes more complicated and challenging.

WUI areas may seem far from urban population centers but what happens in the WUI does not stay in the WUI. New development and roads can help introduce or spread invasive plants and animals to natural areas. Wildfires that begin in the WUI can grow to threaten structures at the edges of cities, destroy city dwellers’ vacation homes, or produce smoke that causes visibility and health problems for people living many miles away. 

NRS researchers are working with university collaborators to map and track the growth of WUI areas in the U.S. using data from 1990 to 2020. The project’s new data set provides the first high-resolution data on WUI change from 1990 to 2020, revealing how housing growth and wildland vegetation have inter-mixed over that 30-year period.

Approach

Using geographic information systems (GIS), the research team integrated U.S. Census and USGS National Land Cover Data to map the wildland-urban interface (WUI) for the conterminous United States from 1990-2020. They used the definition of WUI from the Federal Register (Federal Register 66:751, 2001). The project’s data are useful within a GIS for mapping and analysis at national, state, and local levels.

Outcomes

Increase of area (left) and housing units (right) in the wildland-urban interface, 1990-2020. From the Understanding the Wildland-Urban Interface (1990-2020) StoryMap.

We now have an unprecedented three decades of data on WUI growth, revealing that the area and number of houses in the WUI have grown rapidly across the United States. As of 2020, 9.4 percent of the land area of the contiguous United States is in the WUI, but that land is home to more than 44 million homes — 32 percent of all housing nationwide.

Between 1990 and 2020, there was a 47 percent increase in the number of homes in the WUI and a 31 percent growth in acreage in the WUI. Over the past three decades, the United States added 179,000 square kilometers of WUI, an area equivalent to the state of Washington.

The fastest growth occurred between 1990 and 2010. Expansion of area and housing in the WUI slowed after the 2008 recession as new housing construction declined. Still, 2.6 million homes were built in the WUI between 2010 and 2020.

This research team is committed to continuing to track changes in the WUI and to analyze the 2020 data in new ways in the coming years.