Simulations of firebrand-driven fire spread in landscape-scale Wildland-Urban-Interface (WUI) and urban conflagration models

This study presents an application of a recently developed firebrand model to the case of fire spread in WUI and urban communities using a landscape-scale formulation. The study considers a benchmark configuration corresponding to an array of identical, equally-spaced, square structures; the array is characterized by two length scales: the structure size (SS) and structure separation distance (SSD). Simulations are performed both in one-dimension using MATLAB and in two-dimension using an established landscape-scale fire spread simulator called ELMFIRE. The firebrand model features descriptions of generation, transport and ignition: these were recently introduced for wildland fire applications and are here adapted to the case of WUI/urban fires. Simulations provide an evaluation of the critical conditions that lead to structure-to-structure fire spread, in terms of SSD, wind velocity and firebrand generation rates. The study also includes an evaluation of the model sensitivity to changes in spatial resolution. The model is found to be sensitive to changes in spatial resolution and requires a resolution of less than SS and SSD for grid convergence. These results can be explained by the dominant role of SS and SSD in the WUI/urban fire problem: both length scales need to be captured by the computational grid. • A framework to model firebrand-driven conflagrations in urban areas is presented. • The firebrand model is integrated into a landscape-scale fire spread simulator. • The model features descriptions of firebrand generation, transport and ignition. • The model sensitivity to changes in spatial resolution is evaluated. • It is found that grid convergence requires a spatial resolution of less than 10-m.