Wildfire hazard in the home ignition zone: An object-oriented analysis integrating LiDAR and VHR satellite imagery

• Metrics to characterize the home ignition zone (HIZ) were developed.
• The metrics were calculated for the area of the Fourmile Fire in Colorado.
• The HIZ has less forest and greater spacing between canopies compared to the WUI.
• A simple hazard index was used to identify clusters of relatively high risk HIZes.
• The methods are broadly transferable to other WUI areas.

Many spatially explicit studies of wildfire hazard focus on the wildland–urban interface (WUI), the area where natural vegetation intersects or mixes with structures. However, research suggests that the characteristics of a small portion of the WUI, the home ignition zone, largely determine potential for ignition from wildfire. The home ignition zone (HIZ) is the area that includes a structure and its surroundings out to 30–60 m. The primary goal of this study is to develop metrics to characterize land cover, burned area, and topography in the HIZ. Pre-fire metrics (i.e. related to land cover and topography) help identify relatively hazardous individual HIZes or neighborhoods of HIZes. Post-fire metrics can be used to assess the burned area across land cover types, inside and outside the HIZ. To calculate the HIZ metrics, multiple data sources (e.g. high resolution 8-band multispectral imagery and LiDAR point clouds) were integrated using an object-oriented image analysis. The setting for the study is the Fourmile Canyon area west of Boulder, Colorado, a data-rich area which experienced a large, destructive wildfire in September 2010. The land cover, burn area, and topography metrics were successfully and accurately calculated and then pre-fire metrics were combined into a simple HIZ hazard index. HIZ characteristics broadly mirror the characteristics of the WUI within the fire perimeter as a whole, though the HIZ on average contains more bare and less forest land, has more widely spaced canopies, and experienced less burning during the fire. The HIZ hazard index values were spatially heterogeneous, but with several distinct high and low hazard clusters. The methods described in this study, paired with in situ data collection, can be applied to other areas to inform hazard mitigation plans.