Defining and mapping the wildland-urban interface in Portugal

Abstract

Wildfires in Portugal often threaten urban areas, from small rural villages to the edges of large cities. Regional variations in land use and human settlement patterns originate diverse types of wildland-urban interface (WUI), which need to be mapped to aid decisions concerning landscape-scale fire prevention and suppression. We propose a novel definition of the WUI as the set of line segments where urban areas are in immediate physical contact with flammable vegetation (direct interface), or are less than a pre-specified distance away from flammable vegetation (indirect interface). We also develop a methodology to map it in detail over large areas, based on spatial analysis of the vertices of urban and wildland polygons derived from reclassifying a land cover map. Our approach to WUI delineation mapped 29977 km of direct WUI and 11192 km of indirect WUI in Portugal, and identified substantial regional variations in the length and density of both kinds of WUI, reflecting differences in degree of urbanization and extent of wildlands, and indicating different levels of urban area exposure to wildfires. Addition of fire incidence data to the results of our analysis will permit the development of a WUI typology integrating urban area exposure to wildfires with wildfire threat magnitude, useful for fire management planning at the national level.