Evaluating building-level tree cover change in Southern California wildland-urban interface using high-resolution satellite imagery.

Abstract

Wildfire risks are increasing in wildland-urban interface (WUI) areas due to climate change, fuel accumulation, and human settlement development patterns. Building proximity to tree cover is a major factor in igniting buildings and the specific spatial patterns of buildings further influence fire behavior. While tree cover reduction is one approach to mitigating this risk, our understanding about how tree cover specifically changes around individual buildings remains limited, particularly in the complex social dynamic of urbanization, landscaping practices, and new construction. In this study, coupling high-resolution NAIP imagery with Microsoft building footprints, we examined tree cover change within a 10m buffer around buildings from 2010 to 2022 in Southern California's WUI. Our analysis focused on how these changes differed across building types, categorized by their spatial arrangement, and the impact of new construction on existing buildings. Our findings indicate that 69 % of buildings showed an increase in tree cover within the 10 m buffer, with an average increase of 5.69 %. Notably, very dense and dense clustered buildings, which dominated the study area, exhibited the highest level of tree cover increase. Furthermore, old buildings in proximity to new construction demonstrated a greater increase in tree cover compared to those not near new development. Given the increasing wildfire risk in this area, these findings highlight the importance of community-wide vegetation management to prevent structure-to-structure wildfire spread, and new development policies should consider the possible impact that new construction may have on existing patterns of tree cover and wildfire risk.