Step outside in Singapore on a sunny afternoon, and the heat can be oppressive. Even after sunset, urban areas often remain uncomfortably warm, as heat absorbed by concrete pavement, asphalt roads, and high-rise facades during the day is slowly released back into the night air, resulting in slower nocturnal cooling in urban areas than in rural environments, an effect known as the Urban Heat Island (UHI) effect. Despite being famed for its greenery, residents and visitors alike will tell you that urban heat in this ‘city in a garden’ isn’t just a number – it is felt in every outdoor step, breath, and experience. City streets, like Chinatown, can feel several degrees hotter than shaded parks.

Why traditional heat maps aren’t enough

To be actionable for urban planners, thermal comfort modelling must reflect the microclimatic consequences of planning decisions rather than describe thermal conditions in isolation. Furthermore, many existing thermal comfort modelling studies are constrained by experimental and computational costs and therefore tend to focus on small-scale areas and localised interventions. This means they provide accurate local thermal information, but falls short when it comes to citywide planning. Urban planners need a more planning-centric, scalable, and time-resolved view of thermal comfort across the entire city.

A city-scale thermal comfort model, built for planners

Now, a PhD student, Mr Chen Taihan, with his advisor, Associate Professor Yuan Chao, has developed a city-scale thermal comfort mapping tool that simulates the impact of buildings and trees on the thermal environment, rather than the thermal environment itself. At its core is the Urban Tethys-Chloris (UT&C) model – a physics-based urban canopy model that streamlines input requirements while still producing robust outputs.

Publicly available through the open-access Microclimate Digital Platform (MDP), the tool enables hourly, year-long thermal comfort results at the city scale without relying on computationally intensive techniques such as Computational Fluid Dynamics (CFD). This enables rapid and repeatable evaluations of urban heat exposure to support urban planning and scenario assessment. Importantly, the model preserves the full underlying physical processes, including the drag force of urban greenery on airflow, ensuring that computational efficiency is achieved without compromising scientific rigour.

Understanding Singapore’s heat situation

Using the mapping tool, the team identified pronounced seasonal and daily patterns in thermal comfort despite Singapore’s relatively stable air temperatures. For example, 90% of built-up areas are classified above the Very Strong Heat Stress category at midday in May, while this proportion was only 8.6% in January. Beyond temporal contrasts, the mapping results also reveal substantial spatial heterogeneity in heat stress across Singapore, enabling the identification of several urban heat-stress hotspots. These results highlight the robustness of the tool and underscore the limitations of traditional heat maps.

The researchers showed that building and greenery configurations play an important role in shaping thermal comfort, alongside background meteorological conditions. The results highlight the importance of urban context when designing cooling strategies. In high-density districts, where buildings dominate the microclimate, tree-planning strategies must be tailored to the urban context rather than applied uniformly. Simply adding greenery does not guarantee greater cooling benefits. Instead, trees are most effective with controlled building coverage, where tree shading improves outdoor thermal comfort, and wind permeability among buildings helps alleviate humidity-related discomfort.

To facilitate translation of research findings into policy, this study is supported by public-sector agencies. The MDP is also being adopted by a wide range of stakeholders, spanning government bodies, the World Bank, and universities, and has been applied in urban cities such as Bangkok, Copenhagen, Hong Kong, and Zurich.

Toward human-centric heat resilience

Given increasing urban heat risks, the developed city-scale mapping tool provides planners with an efficient way to design targeted heat-mitigation strategies. The team is also collaborating with Prof Jason Lee from the Heat Resilience and Performance Centre to integrate human-centric data, such as land use, pedestrian volume, and vulnerable populations, to build a more holistic understanding of heat risk and support public-health adaptation.