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

City-scale thermal comfort mapping is essential for identifying urban heat hotspots and assessing residents' thermal responses, especially when integrated with socio-economic data such as population density. However, many existing thermal comfort studies are confined to microscale analyses, short-term durations, or limited scenarios. To address these gaps, we developed a city-scale mapping tool (Fig.1) by integrating a new GIS-based processing scheme of urban morphologies, a high-resolution Digital Surface Model, an urban meteorological observation network, and a mechanistic urban canopy model Urban Tethys-Chloris (UT&C). This tool can rapidly calculate long-term Universal Thermal Climate Index (UTCI) maps for Singapore within a few hours. Model validation against field measurements from three urban precincts and comparisons with mesoscale Weather Research and Forecasting (WRF) simulations demonstrated robust performance. Parametric studies were conducted to investigate the integrated effects of urban features on thermal comfort, including monsoon seasonal variability, greenery coverage changes, and urban gross plot ratio (GPR) adjustments. The key findings are as follows: (1) The calculated results exhibited good performance in both simple street and complex non-street configurations; (2) Incident radiation and air temperature were the dominant background meteorological factors influencing mapping distributions, particularly in Singapore's cloud-prone environment; (3) Analysis at seven representative precincts indicated that high-rise buildings and extensive greenery effectively improved thermal comfort, with a maximum UTCI reduction of 4.0°C; (4) Increasing greenery coverage by 60% resulted in an average UTCI reduction of 0.7°C for the whole Singapore, mitigating extreme heat risk for approximately 10% of built-up areas. The cooling (up to 2.5°C) was most pronounced in low-rise western and eastern regions; (5) Increasing GPR improved thermal comfort citywide but diminished greenery's cooling efficacy and reduced urban ventilation. Our study provides valuable insights into evidence-based greenery planting strategies for urban planning and design, contributing to sustainable urban environments.

Fig.1 Research workflow.