The Urban Heat Island (UHI) effect causes the air temperature to be higher in city centers than in surrounding rural areas. In some cases, the temperature difference can be extreme. As an example: a city of one million people can have a temperature that is as much as 5.4 degrees warmer than the surrounding rural zones.
Several different factors contribute to this problem, but asphalt is a significant heat source in urban areas. Asphalt surfaces, on roads and roofs, absorb warmth and create a radiating effect that releases it back into the surrounding areas, increasing the ambient temperature.
Urban and suburban areas continue to grow, necessitating more roads and roofs. This expanding heat island leads to more energy consumption as people try to cool their homes and buildings. The reliance on air conditioning can strain the energy grid and increase carbon output, which causes global warming.
As cities and suburbs develop, UHI problems grow as well. However, home and business owners can take steps to overcome this human-made issue.
1. Light-Colored Building Materials
One of the primary causes of the urban heat island is the absorption of heat by dark asphalt surfaces. Lighter-colored materials do not absorb heat in the same manner. Instead, they reflect sunlight. Therefore, lighter surfaces do not create the same radiating effect as darker surfaces.
Studies have shown that white-colored materials absorb the least heat, and lighter-colored non-white materials follow close behind. Cement and bricks have a higher thermal mass. They do absorb heat but release it very slowly. Therefore, they remain relatively cool compared to other materials, such as dark-colored asphalt.
2. Green Roofs
A green roof contains plant life. Some famous buildings, including Chicago City Hall, have foliage instead of shingles. These installations are also possible on smaller commercial and residential buildings.
Because they provide shade and do not absorb heat, green roofs are much cooler than conventional ones. According to the EPA, green roofs can be as much as 30 to 40 degrees cooler than traditional roofs.
Small commercial and residential buildings can have green roofs made from hardy plants growing in trays in two to four inches of soil. Though these roofs do not require much maintenance, you need to ensure that your structure is strong enough to support the extra weight.
3. Cool Roofs
A cool roof has reflective properties that keep it from absorbing heat. These roofs can be beneficial when it comes to combating the urban heat island effects. They can also help lower energy costs within a building.
There are different types of cool roofs. Some rely on reflective shingles to avoid heat absorption. Others use metal because of its reflective properties. Some roofers rely on reflective paint or spray-on membranes that reduce solar heat gain.
According to the US Department of Energy, cool roofs can help combat the UHI effect by avoiding the solar heat gain associated with traditional asphalt shingles. The DoE also suggests that the lower temperature on the roof itself can increase its lifespan.
While roof replacement is an option for upgrading to a cool roof, there are also options for applying a coating or glaze to the existing structure to enhance its reflective properties.
Trees, plants, and other vegetation can help combat the urban heat island effect. Trees can provide shade and keep the sun from reaching the asphalt on roads and rooftops. Additionally, this shade can decrease cooling costs for your home.
Home and business owners can plant shade-producing trees that lower the chances of solar heat gain on their roofs and driveways, but they should not ignore other types of foliage.
The process of transpiration can also reduce heat. Transpiration is when plants release water vapor back into the atmosphere through their leaves. This phenomenon is common in rural areas covered by vegetation, but less common in cities with fewer plants.
Property owners can increase the amount of foliage on their land and increase the amount of transpiration that takes place.
5. Green Pavement
According to the EPA, regular pavement can reach temperatures of up to 150 degrees during the summer. When you understand that pavement covers 30% to 45% of the land in many cities, you can see why the temperature difference between urban and rural areas can be significant.
Green pavement products are still in the early stages of development. Some studies have shown the effectiveness of reflective concrete, concrete with reflective paint or glaze, or unique porous pavement.
Though sometimes less practical, replacing pavement with gravel or grass is possible in some situations. Property owners can remove unused paved areas and replace them with vegetation or grass.
6. Energy-Efficient Appliances
Energy-efficient appliances can lower the strain on the electrical grid during hot weather. Air conditioners are the obvious candidates for efficiency upgrades, but you can also consider refrigerators and lighting fixtures.
The EPA’s Energy Star program lists appliances that meet the strictest efficiency standards.
Purchasing Energy Star appliances can reduce power consumption and utility costs. They can also help reduce the UHI effect.
Air conditioners make air cooler inside, but they increase heat output outside. Depending on their power source, the energy needed to run an air conditioning unit also generates heat. The higher the efficiency, the less heat an appliance produces directly and indirectly.
7. Reducing Air Pollution
Air pollution and urban heat island effects go hand in hand. Smog, particles, and other forms of pollution can intensify the heat and lower overall air quality.
Energy consumption and auto emissions are significant culprits when it comes to urban pollution. Driving a more fuel-efficient car, relying on public transportation, or walking and biking when possible can help reduce your contribution to your area’s pollution.
Energy-efficient appliances, such as those with Energy Star certification, can reduce the carbon footprint of your home overall by lowering the amount of energy needed to operate your home.