Owning the WUI: HIZ, HERZ, ITZ
At a small fire workshop in 2007 I called the wildland-urban interface fire "a dumb name for a dumb problem." A dumb name because it was geeky and only half accurate. A dumb problem because technical solutions existed: the WUI fire scene was solvable in ways that managing fires in wildlands and wilderness were not.[i]
Since then exhaustive research on the issue from multiple disciplines has strengthened the technical understanding of why the fires occur and what can mitigate them, so the persistence (even expansion) of such fires leaves them a dumb, if increasingly horrific fire problem. The only advance in the terminology is to drop the "I" from WUI. Has the time come to drop the term, if not the concept altogether?
"Urban conflagration" has staked a claim to replace it. The defining property is that structures furnish the fuel. Fires propagate from building to building; typically trees within the fire's footprint survive. The urban environment might be a metropolitan neighborhood in Los Angeles, a small town in northern California, or clusters of buildings on Bright Angel Point at the Grand Canyon. The surrounding countryside contributes an initiating spark.
Still, geographic distinctions can help parse the larger scene into usable units for analysis. I propose three settings, with respective acronyms.
HIZ is the home ignition zone as conceptualized by Jack Cohen.[ii] It describes the conditions for igniting an isolated structure.
HERZ stands for housing environmental risk zone. It recognizes that fire spreads by contagion and that the collective surroundings affect a fire's capacity to propagate from single structures to communities.
ITZ is the ignition transition zone. It refers to the conditions, geographic and dynamic, that allow points of ignition to initiate the overall chain of conflagration. The originating spark may come from a powerline, a chain dragging behind an RV, a lightning-struck tree, an abandoned campfire; the list is endless. Most are human-caused directly or indirectly, and most are close to communities, which is why they can transition to HIZ and HERZ.
The early characterization of the WUI emerged from the wildland fire community who defined the problem as wildland fires complicated by urban sprawl. It might better have been viewed as urban fires complicated by peculiar landscaping. But once coined, the term helped to imprint the image of wildland fires bursting into communities, for which the Paradise fire (2018) has become the indelible symbol. The most controversial proposals for mitigating the risk from such fires focus on the ITZ, particularly when the zone includes public wildlands.
But the ITZ need not be wildlands. The Oakland Tunnel fire (1991) began within dense housing; the Tubbs fire (2017), from "a private electrical system adjacent to a residential structure"; the Marshall fire (2023), in short grass outside a suburb; the Lahaina fire (2023), in abandoned agricultural fields; the Gatlinburg fire (2016), from multiple powerline failures amid public and private lands; the Woolsey fire (2018), on land sporting an R&D complex owned by Boeing. The Pacific Palisades fire (2025) started in open land adjacent to suburban housing. The Dragon Bravo fire (2025) started by lightning in the backcountry of Grand Canyon's North Rim. What they mostly share is not wildlands but the capacity to metastasize into 'fast fires' whose speed and gusts of embers can overwhelm attempts at control.[iii]
The time has come to take the wildland out of the WUI. These are urban fires with troubled perimeters that can catch fire. ITZ matters: without ignition the fire would not occur. But wildland is only one of a suite of possible ignition zones and not even the most hazardous. Leaving it in the name of the problem misdirects attention to a particular ignition source rather than the combustible sinks and the accompanying high winds that allow a spark to mutate into an urban conflagration. Only treating the ITZ – whatever its character – can still leave the cityscape vulnerable.
What should we call the issue? With tongue slightly in cheek, how about WUZ – wildfire urban zone. We can then make the WUI a has-been WUZ from the past.
[i] Stephen Pyne, "Spark and Sprawl: A World Tour," Forest History Today (Fall, 2008), pp. 4-10
[ii] Jack Cohen - https://www.fs.usda.gov › rm › pubs_journals › 2001 › rmrs_2001_cohen_j001.pdf
[iii] Jennifer K. Balch et al. The fastest-growing and most destructive fires in the US (2001 to 2020). Science 386, Issue 6720 : 425-431 (24 Oct 2024); doi: 10.1126/science.adk5737