Multiscale moderation of shade cooling from neighborhood to street: UAV evidence on pedestrian thermal burden in Incheon, South Korea

Abstract

Shade is widely used to reduce pedestrian heat stress, but its thermal relevance varies across built-environment settings. This study examines shade cooling efficacy as a multiscale context-dependent association between shadow exposure and pedestrian thermal burden. We integrated UAV-derived land surface temperature, ray-casting shadow simulations, and in-situ microclimate observations to estimate thermal burden as the COMFA energy budget (EB) for 1580 street-level cells in Incheon, South Korea. Two shadow metrics were examined: instantaneous (ISSCR) and cumulative (CSSCR) street shadow coverage ratios. Hierarchical linear models (HLM) and generalized additive models (GAM) assessed neighborhood-level variation and street-level nonlinear conditioning. Spatial analyses identified structured mismatch zones — 324 cells with high shadow yet high EB, 187 with low shadow yet low EB — so shadow quantity alone does not ensure lower burden. Random-slope HLMs showed that the shadow–EB relationship varied systematically across five Local Climate Zone (LCZ)-informed neighborhood clusters (ISSCR slopes from −29.128 to −54.851 W/m²), suggesting neighborhood-level contextual moderation. GAM results indicated nonlinear conditioning by vegetation, sky openness, and built form, with the largest modeled EB reductions in vegetation-rich, relatively enclosed streets. ISSCR better captured short-term variation, whereas CSSCR reflected accumulated shading at the neighborhood level. Both shadow metrics were negatively associated with EB overall (ISSCR −47.74 W/m², CSSCR −7.57 W/m²; both p < 0.001), and average EB across the five neighborhood clusters ranged from 119.32 W/m² in Dense Trees to 163.50 W/m² in Open Paved. These findings support place-specific shade strategies for pedestrian heat mitigation and climate-sensitive urban design.