Pervious surface fraction threshold and quantile-based optimization: A novel framework for heat mitigation in high-density urban areas

Urban heat islands significantly exacerbate thermal discomfort, energy consumption, and public health risks in dense urban cores with limited green space. While landscape optimization is a recognized mitigation strategy, practical and quantifiable approaches for highly urbanized areas remain scarce. This study reconceptualizes the city as a continuous mosaic of intertwined grey (built) and green (vegetated) spaces. We apply a “downscale–classify–attribute” framework to analyze Urban Functional Zones along a grey-to-green continuum. Focusing on Beijing’s Fifth Ring Road area, we analyzed 11 landscape metrics across socioeconomic functional zones with Pervious Surface Fraction (PSF) segments (0–1 at 0.05 intervals). Results identified PSF = 0.5 as a critical threshold distinguishing two thermal regulation regimes. Below this value, building patterns (e.g., coverage ratio, height, sky view factor) dominate temperature regulation. In these low-PSF zones (<0.5), a quantile-based optimization framework showed that stringent adjustments (90th/10th percentiles) yielded optimal cooling (up to 2.3 °C reduction) with broader spatial coverage, outperforming moderate and neutral approaches. Above PSF = 0.5, vegetation health (NDVI) becomes the primary regulator. For these areas, maintaining healthy vegetation is the priority. This study provides scientifically-grounded, fine-grained solutions tailored to mixed urban landscapes. Our dual-focused framework—architectural optimization for dense zones and vegetation standards for greener areas—offers a transferable strategy to resolve the urban density–thermal comfort paradox.