Urban Heat Island Mitigation Through Green Infrastructure: A Comparative City Analysis
DOI:
https://doi.org/10.5281/zenodo.22793605Keywords:
urban heat island, green infrastructure, land surface temperature, tree canopy cover, green roofs, urban parks, local climate zones, Landsat thermal remote sensing, comparative city analysisAbstract
Urban heat island (UHI) mitigation is increasingly pursued through green infrastructure, yet evidence on how much
cooling different interventions actually deliver, and whether that cooling generalises across climates, remains
fragmented across single-city case studies that use inconsistent metrics. We compiled a harmonised comparative
dataset for eight cities spanning five Koppen climate classes (Phoenix, Ahmedabad, Barcelona, Melbourne,
Toronto, Berlin, Seoul, and Singapore), combining five summers (2018-2022) of Landsat 8/9 land surface
temperature (LST) retrievals classified by local climate zone with municipal inventories of tree canopy cover, green
roof area, and park geometry, and validated a subset of remote-sensing-derived cooling estimates against
pedestrian-height mobile transects in three cities. A linear mixed-effects model with city as a random effect
estimated that each 10-percentage-point increase in tree canopy cover was associated with a 0.9 degrees C (95%
CI: 0.7-1.1) reduction in mean summer daytime LST, with the effect roughly 60% stronger in hot-arid Phoenix and
Ahmedabad than in temperate-oceanic Berlin, and displaying clear diminishing returns above approximately 40%
canopy cover. Parks larger than 5 hectares produced a measurable park cool island, averaging 2.8 degrees C at
the park boundary and decaying to background temperature within 300-400 m, with cooling magnitude scaling with
both park area and internal vegetation density rather than park area alone. Green roofs cooled roof-surface
temperature substantially (mean 4.1 degrees C) but had negligible, statistically indistinguishable-from-zero effect on
pedestrian-height air temperature at the block scale unless coverage exceeded roughly 30% of rooftop area within a
neighbourhood. Reflective and permeable pavements produced modest daytime LST reductions but measurable
nighttime benefits associated with reduced heat storage release. These results indicate that tree canopy and large,
vegetation-dense parks are the most reliably transferable cooling interventions across climates, that green roofs
mitigate roof rather than pedestrian heat except at high density, and that mitigation strategies calibrated in one
climate should not be assumed to transfer quantitatively to another without local recalibration.
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