Last Updated: Jul 21, 2021
Summer temperatures are finally upon us, and this summer is shaping up to be one of the hotter ones on record (though with global climate change in full swing, this shouldn’t come as a surprise anymore). Heatwaves in much of the country's Southeast part have led to temperatures in the triple digits in May, foreshadowing what could be a pattern for the rest of the summer. For people who live in congested, urban areas, extreme heat can be much more dangerous, as the heat in cities tends to be much more severe.
The urban heat island effect, a well-documented phenomenon, can drastically raise summer temperatures to even more extreme levels. Mercifully, there are things that every urban homeowner can do to help reduce the heat and humidity in the city this summer.
Heat island describes urban areas that are warmer than neighboring rural areas. The Environmental Protection Agency (EPA) states that a city's annual mean air temperature with 1 million people or more can be 1.8–5.4°F (1–3°C) warmer than its surroundings. At night, the difference can be as high as 22°F (12°C). Heat islands can affect communities by increasing peak energy demand during the summer, including air conditioning costs, air pollution, greenhouse gas emissions, heat-related illness and mortality, and water quality.
Across the United States, over two-thirds of significant cities are warming during the summertime at a quicker rate than rural counterparts. Las Vegas, Albuquerque, and Denver are the three cities that most suffer from the urban heat island effect. Las Vegas routinely experiences heat over 7 degrees warmer than the surrounding desert landscape. In addition, due to the urban heat island effect, cities are at a much higher risk of suffering summer days of extreme temperatures. During the past decade, metropolitan areas across the United States experienced at least eight more days, with temperatures soaring above 90 degrees than nearby rural areas.
Urban heat islands essentially follow the path of urban sprawl. As vegetated, rural areas covered with forests, grasslands, and farmlands are cut down, torn up, and replaced with concrete and asphalt structures. The sun’s heat is absorbed, and temperatures inevitably begin to rise. All plant life (and especially trees) play an important role in temperature regulation by absorbing carbon dioxide and evaporating water into the air. On the other hand, concrete and asphalt contribute to higher temperatures by absorbing the sun’s heat instead of reflecting it into the atmosphere. In metropolitan areas, the tunnels of skyscrapers and large buildings trap the hot afternoon heat and significantly reduce wind and airflow. The emissions from hundreds of thousands of vehicles, factories, air conditioners, and other elements of our modern-day civilization contribute to the warming of the urban landscape.
The higher summer temperatures that come with the urban heat island effect have been tied to higher levels of ozone pollution, which can pose a severe health risk for people in the city. With around 80 percent of all Americans living in metropolitan areas, combined with warmer summer temperatures associated with global climate change, the urban heat island effect will only continue to worsen in many regions across the country. Finding ways to reduce the worst effects of urban heat islands is essential to making our summer temperatures bearable.
Here are a few ideas about what you and your neighbors can do to reduce rising temperatures.
Because the urban heat island effect is directly caused by eliminating trees and plants in favor of asphalt and concrete, planting more trees and plants is a simple way to reduce the heat buildup. Trees won’t only keep your home and community cooler by providing shade, absorbing carbon dioxide, and evaporating water. Still, they offer several other significant benefits, including improving urban air quality, reducing stormwater runoff, stopping erosion, and increasing your home's energy efficiency through smart landscaping strategies. Simply put, there is rarely a wrong reason to plant another tree.
Green roofs are growing in popularity across the country as an aesthetically pleasing and thermally efficient alternative to metal and shingles. Several cities across North America have created programs to incentivize homeowners and businesses to incorporate green roofs onto their properties. As an added benefit, the vegetation planted onto a green or living roof will help actively cool the surrounding air in the ways we have explained above. Green roofs add an extra thick layer of roof insulation, which can help prevent that hot summer air from penetrating your home.
Though not as effective as green roofs in reducing the urban heat island effect, cool roofs can play an essential role in keeping your home cooler during the summertime. These types of roofs are made of materials (or include surface coatings on top of an existing roof) that will reflect sunlight and heat back into the atmosphere, thus keeping your home and the surrounding area cooler. For example, EPDM (rubber membrane) roofs, typically black, can be purchased in white for no additional cost.
Though both asphalt and concrete will absorb the heat from the summer sun, a recently poured black asphalt road will feel much hotter due to the absorbent nature of darker colors. Cool pavements use several additives to allow paved surfaces such as roads and sidewalks to reflect, rather than absorb, more solar radiation back into the atmosphere. These pavements can enhance water evaporation which leads to further cooling. Similarly, permeable pavements can reduce the heat from paved surfaces by allowing certain plant life types to abound.
A more energy-efficient home is an essential contribution to fighting against urban heat islands. A more energy-efficient home can reduce the electrical grid's stress and reduce the probability of potentially dangerous power outages during heat waves. Switching to Energy Star certified household appliances is a straightforward way to reduce your energy demand and the related emissions that come with the energy your home uses. In the specific case of an air conditioner, which is often a lifesaver during extended heat waves, the HFCs emitted from an AC unit can trap thousands of times as much heat in the atmosphere as carbon dioxide. Upgrading to a more energy-efficient air conditioner and making sure that yours is operating correctly can reduce greenhouse gas emissions, which ultimately are a direct cause of the increasing heat in cities and worldwide.
People in urban areas tend to have a limited amount of yard space to plant trees and other vegetation to reduce the heat island effect. While you could attempt to “guerrilla-plant” thousands of trees alongside roads and public parks, a better strategy would be to engage with your local elected leaders and advocate for a progressive tree and landscape ordinance that prioritizes planting shade-giving trees throughout the city.
No one likes to be sweltering in the summer. Just becoming aware of the plants and hardscapes around your house—and how they affect the outdoor temperature—is a significant first step. And suppose you have to replace your roof or driveway. In that case, if you are building a patio or deck, or upgrading your landscape, choosing lighter colored materials and planting more trees will make a significant difference in your overall comfort outdoors.
Tobias runs an agroecology farm and a natural building collective in the mountains of El Salvador. He specializes in earthen construction methods and uses permaculture design methods to integrate structures into the sustainability of the landscape.