accumulate more solar heat than the surrounding countryside, producing temperatures that are up to 22℉ (12℃) warmer in the city than in its surrounding rural areas. According to the U.S. Environmental Protection Agency, a city with a population of at least 1 million people is, on average, 1.8-5.4℉ (1-3 ℃) warmer than nearby rural areas¹. The heat island effect in cities occurs because of large areas in cities (approximately 30-45% of the total land cover in cities) are covered in pavement structures and soak up a great deal of solar heat each day².
This heat island in cities increases the demand for energy to cool buildings, increases energy costs, increases pollution, increases the production of greenhouse gases, increases the incidences of heat-caused illnesses and death, and negatively impacts water quality¹.
Methods Used to Reduce the Heat Island Effect in Cities
The following are four primary methods that are used to reduce the heat island effect in cities. Using a combination of these techniques will increase the overall effectiveness of mitigating the heat island effect in a particular city.
- Increase green spaces and trees
The shading of buildings by vegetation decreases the demand for energy used for air conditioning, reducing air pollution and producing fewer greenhouse gas emissions³.
- Green Roofs
Green roofs help to cool the air in cities by providing shade, removing the heat from the air as the vegetation undergoes evapotranspiration, and reducing the surface temperature of the roof itself. Green roof temperatures can be cooler than the surrounding air, compared to the surface temperature of a conventional roof, which can be as high as 90℉ (50℃) warmer than the surrounding air⁴.
Green roofs serve as insulators for buildings, thereby reducing the energy that is needed to heat and cool them. This reduced energy use results in a reduction in air pollution and greenhouse gas emissions. Because the green roofs provides insulation for a building, its occupants will be more comfortable and less likely to experiencing heat stress in the summer⁴.
- Cool Roofs
Because cool roofs absorb less heat, the building below the roof stays cooler, reducing energy demand for air conditioning in the summer, lowering energy use and the associated air pollution and greenhouse gases from energy production, and maintaining greater comfort in the buildings during hot days⁵.
- Cool Pavements
Cool pavements can be made from asphalt and concrete and also by using special coatings and grass paving².