The Impact of Urban Landscape Layouts on Firebrand Spotting

The spotting phenomenon, which involves the transport and deposition of flying burning debris (called firebrands or embers), is a major mechanism associated with the propagation of wildfires. Once generated, firebrands are transported by the local wind and away from the main fire and can ignite secondary fires upon landing. Their trajectory, specially in long-range transports, is mainly controlled by their interactions with the turbulent atmospheric background flow and topography-induced flows. Spotting can be particularly damaging in Wildland-Urban Interface (WUI) regions, where the presence of urban topography modifies the local wind flow. In this work, the effect of urban topography-induced turbulence on the spotting behavior is investigated. Large Eddy Simulations (LES) are used to simulate the turbulent flow over different idealized urban regions. Firebrand particles with time-varying mass, size, and temperature are tracked in the LES flows using a Lagrangian transport model. Differences in their dispersion and deposition statistics are evaluated between the cases in order to assess variations in the spotting risk. The findings of this study can contribute to the improvements of fire risk assessments and management practices in WUI areas.