Wildland-Urban Interface Expansion Increases Risk and Impacts of Wildfires

WUIs are widespread across Australia, Europe, and North America, with the majority located in densely populated regions, such as the southeastern US, eastern China, and western Europe. Globally, the share of land classified as WUI rose from 3.9 percent in 2001 to 4.8 percent in 2020 and is predicted to reach 5.9 percent by 2040. The world population is expected to peak at around 10.3 billion in the mid-2080s, with much of the growth concentrated in sub-Saharan Africa and parts of Asia.  

Alongside population growth, urbanization - particularly rural-to-urban migration and the outward expansion of cities - is a major driver of WUI growth. Currently, over 55 percent of the global population lives in urban areas; this figure is projected to rise to 68 percent by 2050. Urbanization often manifests as unplanned or informal settlements in developing countries, and as planned suburban or second-home developments in developed nations.  

Areas with lower residential densities within the WUI face greater wildfire risk due to richer and continuous fuel loads. As the global population aged 65 and older is projected to more than double to 2.4 billion by 2100, the ageing demographic may influence settlement patterns toward more suburban or peri-urban areas, driven by preferences for larger homes, open spaces, and proximity to nature.  

WUIs are high-risk zones for human-caused wildfires due to the combination of dense wildland vegetation, flammable human structures, and ignition sources from human activity near fuel loads. As population increases within these areas, so does the frequency of activities that can spark wildfires. Expanding real estate development in fire-prone WUI zones further heightens the risk, significantly increasing the potential for property loss.  

WUI areas account for a disproportionate share of wildfire-related property damage because wildfires in these zones occur closer to people and structures. Wildfires pose both direct and indirect risks to businesses. Direct risks include damage to buildings, vehicles, machinery, and infrastructure, as well as operational disruptions. Indirect risks – such as disrupted supply chains or reduced tourism and hospitality - can also be costly. Although the WUI covers less than 10 percent of US land, it is involved in nearly 33 percent of wildfires nationwide. Furthermore, 86-97 percent of building losses due to wildfires in the US occur in the WUI.  

The rapid expansion of the WUI, driven by population growth, urbanization, and demographic shifts, has heightened wildfire risks and their associated impacts. This growth contributes to an increased likelihood of human-caused wildfires, property damage, and economic losses. Continued development in these fire-prone zones further intensifies these challenges, posing significant risks to residents, businesses, and critical infrastructure. 

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