Classification Of The Wildland Urban Interface For Fire Risk Analysis In Los Angeles County California

Wildfires in California play an important role in many ecosystems; however, when frequency rises, they can have deleterious effects on native flora and fauna. For humans living in vulnerable areas, wildfire can threaten the property and lives of residents. This is of particular concern for those living in the wildland-urban interface (WUI), where urban and open lands meet. Identifying areas making up the WUI and assessing fire risk is critical for proper land management. However, common definitions of these areas are quite general, often relying solely on a distance from housing structures to wildland vegetation or a threshold population density. In California, where wildfire occurrence has become prolific in recent years, the most recent effort to map high risk areas was carried out in the early '90s and has not been updated since. This study employed a method of WUI delineation developed by Lampin-Maillet et al. (2009) using housing density, vegetation aggregation, and terrain criteria to identify factors that contribute to wildfire risk (ignition density) and severity (burned area). In addition, classification of the interface area based on these factors allowed for an exploration of their interactions and the identification of areas that face particularly high wildfire risk or severity. This was done with the goal of determining where fire prevention resources and practices could be employed with the greatest benefit. It was determined that the WUI area in a subsection of Los Angeles County occupied 208,718 ha. Fire occurrence data including 1,802 fire ignition points and fire perimeters covering 139,178 ha were used to explore the relationship between fire risk and severity between classes of three risk factors. In addition 18 different WUI types were defined by combining classes of each risk factor to identify the combination of risk factors that results in the greatest wildfire risk or severity. It was found that housing density was the most important factor in determining wildfire risk, while slope was the most important in determining severity. Areas of intermediate housing density (1.2 houses/hectare) were at the greatest risk and experienced the greatest severity. Areas of high vegetation aggregation experienced the greatest severity, but the lowest risk. Finally, due to significantly high wildfire risk, the Castaic, Acton/Agua Dulce, and Leona Valley areas were identified as being ideal candidates for fire prevention programs focused on resident education and awareness. Given continued urban growth in Los Angeles County and the spread of urban development into wildland territory, this information will be critical to future decisions in urban planning and land management as well as to the direction of fire prevention resources.

In 2002 much of the Front Range of the Rocky Mountains in Colorado was rich in dry vegetation as a result of fire exclusion and the droughty conditions that prevailed in recent years. These dry and heavy fuel loadings were continuous along the South Platte River corridor located between Denver and Colorado Springs on the Front Range. These topographic and fuel conditions combined with a dry and windy weather system centered over eastern Washington to produce ideal burning conditions. The start of the Hayman Fire was timed and located perfectly to take advantage of these conditions resulting in a wildfire run in 1 day of over 60,000 acres and finally impacting over 138,000 acres. The Hayman Fire Case Study, involving more than 60 scientists and professionals from throughout the United States, examined how the fire behaved, the effects of fuel treatments on burn severity, the emissions produced, the ecological (for example, soil, vegetation, animals) effects, the home destruction, postfire rehabilitation activities, and the social and economic issues surrounding the Hayman Fire. The Hayman Fire Case Study revealed much about wildfires and their interactions with both the social and natural environments. As the largest fire in Colorado history it had a profound impact both locally and nationally. The findings of this study will inform both private and public decisions on the management of natural resources and how individuals, communities, and organizations can prepare for wildfire events.

Urban encroachment into chaparral areas has accelerated the fire-flood-erosion cycle. Preventive maintenance measures can help reduce the damage from fire and flood. This report describes the chaparral environment; how to cope with problems in watershed management, how to landscape for fire and soil erosion control, how to plan for home safety from fire, how to treat newly burned chaparral slopes, how to clear brush around homes; and what to do when caught in a wildfire. The information reported is addressed to homeowners, buyers, and developers; and architects, planners, and other officials in muncipalities and agencies.