As temperatures in cities rise due to climate change, city developers and designers must develop effective ways to reduce urban heat. A recent study headed by UCL (University College London) academics, released in the journal Geophysical Research Letters, sheds fresh light on how various urban heat management systems affect city temperatures. The study emphasizes the large cooling advantages of cool roofs over other alternatives such as rooftop gardens, street-level greenery, solar energy panels, and air conditioning systems.

Study Summary:

The study used a 3-D urban climate simulation for Greater London to assess the thermal impacts of different active as well as passive heat management methods. The investigation concentrated on the two warmest days of the 2018 summer, which were the hottest on record, to evaluate each method’s full potential. The methods evaluated included:

  • Painted cool roofs
  • Rooftop solar energy panels
  • Rooftop Gardens
  • Street-level tree vegetation
  • Air conditioning


The key outcomes of the study are:

Painted Cool Roofs:

The study discovered that cool roofs, typically either painted white or coated with a reflecting coating, are among the most effective techniques for urban living. If broadly adopted across London, cool roofs have the potential to reduce outdoor temperatures by an average of 1.2 Celsius degrees, with decreases of up to 2 degrees Celsius possible in select areas. Cool roofs have the dual benefit of reflecting heat rather than absorbing it, which cools down both the exterior environment and the interior of structures.

Rooftop Gardens and Street-level Vegetation:

While green roofs provide advantages such as water retention and wildlife habitats, they have been shown to have a minor net cooling impact on the city. The study found that the cooling impact of green roofs varies throughout the day. During the hottest months, green roofs can reduce metropolitan temperatures by approximately of 0.5 Celsius degrees. However, this cooling impact was negated overnight since the heated mass of the roofs held daytime heat, expelling it when the sun went down while increasing the temperature at night by almost the same amount.

Street-level vegetation, notably the change of urban greenery from grassland to deciduous trees, was discovered to have varied effects. Trees could reduce temperatures overnight, but they would most certainly raise temperatures during the day and air humidity, hurting people’s thermal comfort.

Solar Energy Panel and Air Conditioning:

Solar panels had a modest net cooling influence of roughly 0.3 Celsius degrees on average in London. They do, however, provide additional environmental advantages, such as the creation of renewable energy.  

In contrast, air conditioning has been shown to cozy up the outdoor atmosphere. While it cools building the interior, it also transmits heat to the outside, raising outdoor temperatures by roughly 0.15 degrees Celsius generally and by up to 1 degree Celsius in densely populated places.

Research Methodology:

To assess each method’s entire potential impact, the research team simulated its widespread adoption across Greater London’s residences, commercial, and industrial buildings. This comprehensive strategy enabled the researchers to examine the efficacy of several heat reduction techniques under identical settings.

Lead author Dr. Oscar Brousse of UCL’s Bartlett School of Environment, Energy, and Resources explained, “We thoroughly tested various techniques that major cities like London could employ to adapt to and mitigate rising temperatures, and discovered that cool roofs seemed the most effective way to keep temperatures lower during extremely scorching summer days. Other approaches provided other important side effects, but none succeeded in lowering outdoor urban temperatures to quite the same extent.”

Impacts of Urban Planning:

As cities grow and environmental conditions change, urban areas become particularly susceptible to the Urban Heat Island (UHI) impact, in which cities trap heat, resulting in increased discomfort and fatality rates during heat waves. This study provides useful information for urban designers and planners looking for effective solutions to adapt to and manage rising temperatures.

The data indicate that focusing on cool roofs is a highly effective technique for lowering urban temperatures. Other alternatives, including green roofs and plants, provide additional ecological and aesthetic benefits, but their impact on lowering city heat is less significant.

Prospective Studies:

Additional research is required to investigate the long-term effects and practicality of implementing these tactics on a large scale. The study’s findings rely on modeling and simulations, therefore real-world applications may provide new issues and variables. Continued collaboration among researchers, municipal developers, and legislators will be critical to creating and improving successful urban heat management technologies.

Further Insights:

The study also shed light on the potential tradeoffs and combined consequences of various heat control technologies. For example, while air conditioning may greatly chill indoor spaces, its widespread use may increase outdoor heat. However, the researchers discovered that the additional energy consumption from air conditioning equipment might be wholly supported by renewable solar panels if fully installed, potentially countering some of the negative effects.

The study emphasizes the importance of taking an extensive approach to city heat administration, taking into account not only temperature lowering but also issues such as energy usage, humidity, and total environmental impact. The study provides towns with a path for adapting to and mitigating the effects of Climate Change.


The study was funded by Wellcome and the Natural Environment Research Council (NERC), emphasizing the necessity of multidisciplinary approaches to tackle complex climate concerns.


The UCL-led study emphasizes the need to select appropriate heat management technologies to effectively counteract urban warming. Cool roofs appear as an exceptionally effective approach for cooling cities such as London, providing large temperature decreases and multiple advantages for both outdoor and indoor settings. While other solutions have their advantages, cool roofs are the greatest alternative for regulating urban temperatures during severe heat events.