Refining Wildland-urban interface delineation: A building-level exposure assessment framework

Conventional wildland-urban interface (WUI) delineation commonly relies on fixed thresholds for building density, vegetation cover and distance, which may not fully represent building-level differences in fuel-related exposure across heterogeneous landscapes. Here, we propose a method to delineate the WUI based on building-level wildfire exposure. We developed two random forest models to quantify both the exposure status and exposure intensity of structures. Key predictors and thresholds were identified using Shapley Additive Explanations (SHAP) and partial dependence plots (PDPs) to identify buildings with high exposure potential and their surrounding vegetation. Building density and the Vegetation Fire Spread Index (VFS) were primarily associated with exposure status, whereas vegetation density was mainly associated with relative exposure intensity. Historical burned areas accounted for 5.25% of the resulting WUI area, compared with 2.42% under the Federal Register-based framework. Historically exposed buildings represented 24.48% of buildings within the resulting WUI, compared with 18.65% under the Federal Register-based framework. By linking building selection with surrounding wildland fuels, this framework provides a spatial basis for local building-exposure screening and differentiated wildfire mitigation.