The Esperanza Fire: Comparison of coupled atmosphere-fire model simulation and FireMapper thermal imaging data

The ignition of the Esperanza Fire was reported on October 26,2006, at the base of a drainage near Cabazon, CA, during a strong Santa Ana wind event. The next morning, five wildland firefighters were overrun by the fire's run up the steep drainage below their position. The authors of the incident fatality report hypothesize that at the time of the burnover, a rapid, sudden run of the fire occurred due to a complex alignment of meteorological, terrain, and fuel factors.

In this work, we use a coupled atmosphere-fire model initialized with a MM5 mesoscale simulation of the region to examine the meteorological flow in the vicinity of the fire, model the fire growth and interaction with the atmospheric flow, and compare with measurements collected during the first few days of the fire. This verification data includes remote sensing data from FireMapper, an infrared imaging spectrometer on board the PSW Airborne Sciences Aircraft which produced imagery from numerous passes in the early period of the fire. FireMapper measures the radiance in a segment of the thermal band, which penetrates through smoke.

The results to date, firstly, show many aspects in agreement between the modeled fire behavior and that shown in the thermal data, including rapid spread downwind, and rough agreement in area, shape, and direction of spread at periods for which fire location data is available. Secondly, results show that the atmospheric flow evolves from complex atmospheric dynamics leading to an acceleration of the winds near the surface. Although the winds vary in space, in the vicinity of the fire, the model suggests they are easterly, not aligned with the drainage, near the surface and back towards northeasterly, in alignment with the drainage, with height. The overall flow pattern shows an acceleration in the location of the fatality, but the energetics contributing to this and whether the alleged inversion contributed to this through the capping/squeezing mechanism suggested in the report require further investigation, as well as the feedback from the fire to the flow. Thirdly, the fire plume penetration through the apparent inversion is the result, rather than the cause, of rapid fire growth up the drainage.