The urban heat island (UHI) effect, where cities experience significantly higher temperatures than rural areas, has become a pressing issue. The UHI results from the extensive use of heat-retaining materials like asphalt and concrete, combined with limited vegetation and shading. The UHI effect drives up energy consumption, worsens air quality, and can impact health. By examining five common passive cooling methods and their impact on the local microclimate, urban planners and architects can make informed choices to improve comfort in public spaces.
Using ENVI-met’s simulation data, this article explains how certain surfaces affect city temperatures. ENVI-met from One Click LCA is a microclimate simulation software that helps urban planners and architects analyze these effects by modeling how different materials impact temperature, shading, and air movement. By using ENVI-met, professionals can assess the thermal behavior of various materials in real-world scenarios, allowing them to make informed decisions to improve urban comfort and sustainability.
Learn more about the five passive cooling methods and their impact on urban comfort below.
Asphalt and concrete are widespread in city infrastructure — used in roads, parking lots, and sidewalks. Pavements made from concrete or asphalt absorb and store up to 95% of solar radiation due to their dark colors and dense composition. ENVI-met simulations demonstrate that these surfaces heat up quickly and stay warm for longer periods, even after sunset. This retained heat is slowly released into the air, mitigating nighttime cooling.
The materials chosen for roofs, including the insulation layers, play a critical role in determining how much heat a building absorbs at its most exposed surfaces. ENVI-met data indicates that roofs with darker, dense materials such as concrete retain more heat, raising the air temperature in surrounding areas. In contrast, less dense and lighter materials, such as terra cotta, absorb less heat, resulting in a smaller impact on air temperatures. Modern cool roof coatings, which reflect most incoming radiation, show an even lower influence on air temperatures, further mitigating the localized heating effect. Next to the artificial solutions, nature-based roof systems such as green roofs can also be beneficial for local climate conditions. The case study from Kolkata supports these findings, highlighting how roof greening can further reduce heat stress.
Adding vegetation to building walls can substantially reduce temperatures. ENVI-met simulations highlight how green façades can reduce outside wall temperatures by as much as 20 degrees, compared to walls made of concrete or other exposed materials. The cooling effects come from a combination of shading and transpiration cooling provided by plants, which improves both thermal comfort for humans and the energy efficiency of buildings. Similarly, adding parks and small green spaces can significantly enhance cooling, as emphasized in the article on the role of urban design in reducing city temperatures.
Urban planners increasingly use water features like fountains or misting systems to cool down public spaces. ENVI-met’s analysis shows that water features help lower the air temperature by converting heat into moisture through vapourization. This process creates a cooling effect that can be felt in the immediate vicinity. Adding well-placed water features in high-traffic areas can significantly enhance outdoor comfort. However, this solution has a limited impact in regions with high air humidity. This example highlights the necessity of tailoring solutions to address local conditions, given the diversity and complexity of urban environments and heat mitigation strategies. ENVI-met meets this need by allowing the application and assessment of site-specific strategies that adapt to each unique characteristic.
Designing spaces that allow for air movement can make a notable difference in thermal comfort. ENVI-met studies indicate that when ventilation channels are included, the heat can be reduced faster. Combined with lighter pavements and other cooling materials, this approach can help alleviate the intense heat often experienced in enclosed urban areas like courtyards.
The urban heat island effect poses challenges for energy consumption, environmental sustainability, and public health. Passive cooling strategies — such as selecting appropriate materials, incorporating vegetation, and optimizing urban airflow — offer effective ways to reduce urban overheating.
ENVI-met simulations provide valuable insights into how different materials and design choices influence urban microclimates. By leveraging such data, urban planners and architects can develop targeted solutions that improve thermal comfort, reduce energy demand, and create resilient, climate-adaptive cities. Implementing these strategies can lead to healthier, more sustainable urban environments.