The wildland-urban interface (WUI) is the area where houses and wildland vegetation meet or intermingle, and where wildfire problems are most pronounced. Here we report that the WUI in the United States grew rapidly from 1990 to 2010 in terms of both number of new houses (from 30.8 to 43.4 million; 41% growth) and land area (from 581,000 to 770,000 km; 33% growth), making it the fastest-growing land use type in the conterminous United States. The vast majority of new WUI areas were the result of new housing (97%), not related to an increase in wildland vegetation. Within the perimeter of recent wildfires (1990-2015), there were 286,000 houses in 2010, compared with 177,000 in 1990. Furthermore, WUI growth often results in more wildfire ignitions, putting more lives and houses at risk. Wildfire problems will not abate if recent housing growth trends continue.

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Globally, and in the US, wildfires pose increasing risk to people and their homes. Wildfire management assumes that buildings burn primarily in the wildland–urban interface (WUI), where homes are either ignited directly (especially in intermix WUI areas, where houses and wildland fuels intermingle), or via firebrands, the main threat to buildings in the interface WUI (areas with minimal wildland fuel, yet close to dense wildland vegetation). However, even urban areas can succumb to wildfires. We examined where wildfire damages occur among urban, rural and WUI (intermix and interface) areas for approximately three decades in California (1985–2013). We found that interface WUI contained 50% of buildings destroyed by wildfire, whereas intermix WUI contained only 32%. The proportion of buildings destroyed by fires among classes was similar, though highest in interface WUI areas (15.6%). Our results demonstrate that the interface WUI is where most buildings were destroyed in California, despite less wildland fuel. Continued advancement of models, mitigation and regulations tailored for the interface WUI, both for California and elsewhere, will complement the prior focus on the intermix WUI.

Over the past 30 years, the cost of wildfire suppression and homes lost to wildfire in the US have increased dramatically, driven in part by the expansion of the wildland–urban interface (WUI), where buildings and wildland vegetation meet. In response, the wildfire management community has devoted substantial effort to better understand where buildings and vegetation co-occur, and to establish outreach programs to reduce wildfire damage to homes. However, the extent to which the location of buildings affected by wildfire overlaps the WUI, and where and when outreach programs are established relative to wildfire, is unclear. We found that most threatened and destroyed buildings in the conterminous US were within the WUI (59 and 69% respectively), but this varied considerably among states. Buildings closest to existing Firewise communities sustained lower rates of destruction than further distances. Fires with the greatest building loss were close to outreach programs, but the nearest Firewise community was established after wildfires had occurred for 76% of destroyed buildings. In these locations, and areas new to the WUI or where the fire regime is predicted to change, pre-emptive outreach could improve the likelihood of building survival and reduce the human and financial costs of structure loss.

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The wildland–urban interface (WUI) is a focal area for human environmental conflicts including wildfires. The WUI grows because new houses are built, and in developed countries, housing growth can be very rapid in areas with natural amenities. However, it is not clear if natural amenity-driven WUI growth is limited to developed countries, or also prevalent in developing countries. Amenity-driven WUI growth may be particularly rapid there, owing to a rapidly growing middle class. Our objectives were to (i) map the current WUI; (ii) quantify recent WUI growth; and (iii) analyse relationships between the WUI and both fire ignition points and wildfire perimeters in the region of El Bolson, in Central Andean Patagonia, Argentina. We mapped the current WUI based on housing information derived from census data, topographic maps, high-resolution imagery and land-cover data. We found that the WUI contained 96.6% of all buildings in 2016 even though the WUI covered only 6.4% of the study area. Between 1981 and 2016, the WUI increased in area by 76%, and the number of houses by 74%. Furthermore, 77% of the recent fires in the region occurred in the WUI, highlighting the need to balance development with wildfire risk and other human–environmental problems.

Forests historically associated with frequent fire have changed dramatically due to fire suppression and past harvesting over the last century. The buildup of ladder fuels, which carry fire from the surface of the forest floor to tree crowns, is one of the critical changes, and it has contributed to uncharacteristically large and severe fires. The abundance of ladder fuels makes it difficult to return these forests to their natural fire regime or to meet management objectives. Despite the importance of ladder fuels, methods for quantifying them are limited and imprecise. LiDAR (Light Detection and Ranging), a form of active remote sensing, is able to estimate many aspects of forest structure across a landscape. This study investigates a new method for quantifying ladder fuel in the field (using photographs with a calibration banner) and remotely (using LiDAR data). We apply these new techniques in the Klamath Mountains of Northern California to predict ladder fuel levels across the study area. Our results demonstrate a new utility of LiDAR data to identify fire hazard and areas in need of fuels reduction.Remote Sens. 2016, 8, 766 2 of 23 90% of trees are killed), which have been increasing [10,11]. These altered contemporary fire patterns are due to a number of factors, but considerable increases in surface and ladder fuels play an important role [12]. Ladder fuels allow fire to transition into overstory tree crowns by providing greater vertical fuel continuity, and fire burning ladder fuels also preheats canopy fuels that have not yet ignited [13]. Additionally, dense ladder fuels can make suppression more difficult and increase wildland firefighter exposure to hazardous conditions, especially when fire behavior shifts unexpectedly, by inhibiting escape to safety zones [14]. In addition to the biophysical influences of ladder fuels on fire behavior and fire management, they can also reduce habitat quality through decreasing accessibility and foraging efficiency for wildlife and tribal subsistence gathering [15].Despite the importance of ladder fuels to fire behavior, effects, and firefighter safety, they have not been directly quantified except in a few cases [13,16,17], all of which are sampled on the ground, with no explicit connection to remote sensing. Because ladder fuels are below the canopy, passive remote sensing platforms are not able to capture their composition, except in very open forests. In most cases, fire models utilize a surrogate for ladder fuels, which is comprised of a combination of canopy base height (CBH) and fuel model (sometimes with an adjustment of fire behavior) [18]. CBH is the height above which there is enough fuel per unit volume to carry the fire upward. The fuel density necessary to carry fire is most commonly 0.012 kg·m −3 [19], but other thresholds have been suggested and used [20][21][22][23].In addition to a variable fuel density threshold, estimations for CBH are commonly based on allometric equations, moving them further from a consistent direct measurement. Although activ...

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