Evaluating dynamic wildfire evacuation trigger buffers using the 2003 Cedar Fire

Despite threats posed to communities from wildfire, few tools exist to aid emergency managers in recommending evacuations. An evacuation trigger buffer is a pre-established boundary encompassing a community or asset that triggers an evacuation recommendation should a fire cross the edge of the buffer. The Wildland–Urban Interface Evacuation model (WUIVAC) delineates evacuation trigger buffers based on modeled fire-spread rates and estimated evacuation times. A point along the edge of a WUIVAC-generated trigger buffer represents the modeled shortest time required for a fire to travel to a community. The objective of this research is to use data from the 2003 Cedar Fire in southern California to evaluate the temporal and spatial differences between evacuation trigger buffers as generated by WUIVAC and the perimeter and spread of a historical fire. Three trigger buffers surrounding a test community were created for hourly increments and analyzed in conjunction with the equivalent hourly locations of the leading edge of the Cedar Fire. The novel use of forecast winds yielded dynamic trigger buffers that varied with changes in wind speed and direction. The modeled trigger buffers exceeded the actual fire front by as much as 126 m for the 1-h buffer and 1400 m for the 3-h buffer, which implies that evacuees would have had slightly more time for evacuation than indicated by the trigger buffers. Had WUIVAC been used operationally during this event in the manner presented in this paper, it would have likely been successful in triggering an evacuation with enough time for the community to safely evacuate. This research represents a first step towards validating WUIVAC-modeled evacuation trigger buffers.