The rising threats of global wildland-human interface revealed by a scale-adaptive approach

The Wildland-Human Interface (WHI), where human infrastructure and activities meet or intermingle with wildland vegetation, represents a critical zone of human-environmental conflict. Here, we present the first global map to explicitly differentiate the WHI into its Wildland-Urban Interface (WUI) and Wildland-Agriculture Interface (WAI) components between 2000 and 2020, using a scale-adaptive HEALpix Quadtree algorithm. We show that the global WHI covered 4.87% of terrestrial area in 2020, with the WAI (4.68%) being significantly more extensive than the WUI (0.19%). Over the two decades, the global WUI area expanded dramatically by 59.76%, whereas the WAI area experienced a net decrease of 3.26%. This marginal net change in WAI masks high spatial turnover. Major losses of original WAI due to agricultural expansion were largely compensated by gains in new WAI elsewhere. Notably, 5.03% of the world's key protected areas were affected by WHI encroachment over this period. Our analysis reveals that the type of WHI has distinctly shaped both wildfire regimes and biodiversity gradients. These findings underscore the critical need for establishing a global WHI monitoring network to mitigate rising threats to ecosystems and human security.