The ignition index based on flammability of vegetation improves planning in the wildland-urban interface: A case study in Southern Spain

Forest fires in the wildland urban interface (WUI) are a widespread and growing problem due to changes in land use and climate. The impacts of WUI fire depend on the exposure of homes to dense vegetation (both natural and ornamental), as well as fire intensity, which is determined by meteorological, topographical, and vegetation conditions. In this study, our goal was to identify the ignition index in one risky Mediterranean WUI based on the potential flammability of the main intermix species at the particle level. The flammability of 18 species (natural and ornamental) commonly found in southern Spain was analyzed at the particle level. Flammability experiments ranked the flammability of the different species from moderately flammable to extremely flammable. Flaming duration (a variable related to fire suppression difficulty) and the ignition coefficient of the surrounding vegetation helped to complete the ignition risk for each vegetation aggregation. Thuja orientalis and Ligustrum vulgare showed the greatest individual potential to mitigate fire spread, and are recommended for planting and use as landscaping hedges in the Mediterranean WUI. We concluded that this methodological procedure is a useful tool for prioritization and budget allocation of fire risk reduction treatments. Furthermore, the development of technical guidelines for public urban landscaping as well as landscaping on private residences is required to adequately address and mitigate fire impacts both on homes and the surrounding landscapes.