[Article] Human Interaction with Urban Morphology under the Influence of Urban Heat Island: A Systematic Review

What if one of the most powerful tools for protecting people from extreme heat is already embedded in the shape of our streets?

Urban heat is not determined by temperature alone. It is also shaped by the height and spacing of buildings, street orientation, access to shade, surface materials, vegetation, water, wind, and, most importantly, the people using these spaces.

Our systematic review, published in the Journal of Daylighting, examines how urban morphology influences microclimates and pedestrian thermal comfort under the urban heat island effect. Starting from 1,901 scientific records, we systematically screened the literature and synthesized evidence from 186 studies published between 2015 and 2025.

The findings reveal a fundamental message: urban form is climate infrastructure.

• Dense urban areas can provide valuable shade during the day, but they may also restrict ventilation and retain heat after sunset. Studies report that urban canyons and impermeable surfaces can raise nighttime temperatures by 2 to 5°C.

• Street orientation matters. East-west streets often experience greater heat exposure because of prolonged solar radiation, while diagonal orientations can distribute solar gains more evenly.

• High-albedo materials can reduce surface heating, with some studies reporting surface-temperature reductions of up to 5°C. However, reflective materials may also increase radiant heat at pedestrian level if they are introduced without adequate shade.

• Trees are among the most effective cooling measures. Evidence from the reviewed studies shows that shade trees can reduce surface temperatures by around 3.1°C, while dense planting in hot-arid conditions reduced Physiological Equivalent Temperature by as much as 16.9°C.

• In Cairo, increasing tree-canopy coverage to 35 to 50% reduced afternoon PET by more than 5°C, while efficient irrigation lowered water use by 85%.

• Urban water bodies can reduce nearby air temperatures by up to 3°C during peak heat, but their effectiveness depends on climate, humidity, size, depth, location, and connection to prevailing winds.

Yet the central lesson goes beyond geometry and temperature. A thermally comfortable city cannot be designed for a standardized, imaginary pedestrian.

Age, gender, health, clothing, activity, culture, thermal history, expectations, and the ability to seek shade all influence how heat is perceived. Two people can walk through the same street under the same measured conditions and experience very different levels of thermal stress.

This is why outdoor thermal comfort is not simply an engineering metric. It is a question of public health, social inclusion, and climate justice. Children, older adults, outdoor workers, people with health conditions, and those who cannot change when or where they travel may face much greater exposure.

To translate this knowledge into practice, we developed a five-layer parametric Design Tool connecting:

• urban density, street geometry, orientation, and materials;

• temperature, wind, humidity, and solar radiation;

• thermal-comfort indicators such as PET, UTCI, and PMV;

• physiological and psychological differences; and

• behavioral, personal, social, and cultural adaptation.

The framework allows designers and planners to explore alternative urban configurations, anticipate their microclimatic consequences, and evaluate how different groups may experience the resulting spaces.

The practical implication is clear: there is no universally “cool” urban form. A narrow canyon may offer essential shade in a hot, dry climate but restrict airflow in a humid one. Trees may provide strong summer benefits but reduce desirable solar access during cold seasons. Water can cool the surrounding air but increase humidity. Reflective surfaces can reduce stored heat while increasing pedestrian radiant exposure.

Climate-responsive urban design therefore requires combinations of measures that are adapted to local climate, season, time of day, urban activity, and population.

As heatwaves intensify, we should no longer ask only, “How can we reduce urban temperatures?” We must also ask:

Who uses this space, when are they exposed, and will the city’s form protect them when extreme heat arrives?

Congratulations to Fataneh Shoghi, Seyed Morteza Hosseini, Shahin Heidari, Julian Wang, Mohammadjavad Mahdavinejad, and all collaborators involved in this work.

📘 Full article: https://doi.org/10.15627/jd.2025.28

📚 Learn more about our research: https://www.sbd.uliege.be/

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