A city-scale mapping tool for assessing effects of urban greenery and morphologies on thermal comfort: A case study in Singapore

Given increasing urban heat risks, city-scale thermal comfort mapping is significant for identifying hotspots and assessing residents' thermal responses. However, many existing thermal comfort studies remain limited to microscale analyses, short-term durations, or limited scenarios. To address these gaps, we developed a city-scale mapping tool by integrating a new GIS-based processing scheme of urban morphologies, an urban meteorological observation network, and a mechanistic urban canopy model, Urban Tethys-Chloris (UT&C). The tool enables year-round, hourly calculations of the city-scale Universal Thermal Climate Index (UTCI) at 200 m resolution with high computational efficiency. The key findings are as follows: (1) Model validation using on-site measurements at three sites and comparison against meso‑scale modelling demonstrate strong performance, with RMSE for UTCI and air temperature (T_a) below 1.5 °C and 0.9 °C, respectively; (2) Temporal analysis reveals that May and early afternoon hours are periods of peak thermal burden, with over 90 % of grids exceeding the Strong Heat Stress threshold; (3) Morphological analysis identifies built-up fraction (f_built), wall surface fraction (λ_wall), and tree coverage (f_tree) as key drivers of thermal exposure. Interaction regressions reveal that high λ_wall suppresses trees’ cooling, with the cooling potential of f_tree declining from –10.98 °C to –1.20 °C when increasing λ_wall; (4) Spatial clustering identifies five hotspot zones, each shaped by distinct morphological and greening constraints. The findings support differentiated intervention strategies, where low-enclosure areas benefit from greening enhancement, and high-enclosure districts require morphological openness. This tool offers planners a diagnostic and efficient approach for designing targeted urban heat mitigation strategies.