Wildland–urban interface
The US Forest Service defines the wildland–urban interface qualitatively as a place where "humans and their development meet or intermix with wildland fuel.
A quantitative definition is provided by the Federal Register, which defines WUI areas as those containing at least one housing unit per 40 acres (16 ha).
The Federal Register definition splits the WUI into two categories based on vegetation density: Human development has increasingly encroached into the wildland–urban interface.
Factors include geographic population shifts, expansion of cities and suburbs into wildlands, and vegetative growth into formerly unvegetated land.
The introduction of non-native species by humans through landscaping can change the wildlife composition of interface regions.
[12] Additionally, disease vectors in isolated patches can undergo genetic differentiation, increasing their survivability as a whole.
[13] In North America, Chile, and Australia, unnaturally high fire frequencies due to exotic annual grasses have led to the loss of native shrublands.
[4] Wildfires in the United States exceeding 50,000 acres (20,000 ha) have steadily increased since 1983; the bulk in modern history occurred after 2003.
[15][16] The diverse demographics in these areas —ranging from elderly populations to young families— require tailored evacuation strategies to accommodate different vulnerabilities and safety needs.
[17] Effective WUI evacuation planning must balance early warning systems, clear communication, adequate infrastructure, and community engagement to enhance preparedness and ensure rapid, safe responses in emergencies.
Areas at the highest risk are those where a moderate population overlaps or is adjacent to a wildland that can support a large and intense wildfire and is vulnerable with limited evacuation routes.
[5] The vulnerability factor category is measured with evacuation time through a proximity of habitable structures to roads, matching of administrators to responsibilities, land use, building standards, and landscaping types.
However, factors are dynamic and a constant representation comes at a cost of a limited window and thus MTT is only applicable to short-timescale simulations.
Three groups are responsible for achieving the three WUI objectives, these are land management agencies, local governments, and individuals.
The key benefit of fire-adapted communities is that a reliance on individuals as a core block in the responsibility framework reduces WUI expenditures by local, regional, and national governments.
[24] The HIZ is a guideline for whoever is responsible for structure wildfire protection; landlords and tenants (homeowner if they are the same) are responsible for physically constructing and maintaining defense zones while local government defines land use boundaries in a way that defense zones are effective (note: fire-resistant is arbitrary and is not defined in hours of resistance for a given degree of heat; these guidelines are relaxed for non-evergreen trees which are less flammable; this guide is not intended to prevent combustion of individual structures in a wildfire—it is intended to prevent catastrophic wildfire in the WUI): There are three challenges.
[27] The Camp Fire demonstrated limitations of the fire-adapted community theory in late season wildfires driven by Katabatic winds, and in the land management agencies' responsibility in controlling infrastructure ignition sources.
