What to know about urban heat islands

Cities, environmentalists are trying to get a handle on these and the problems they cause

Stock image. Timea Kadar (Pexels)

Have you ever walked a block in the same city, and all of a sudden, you felt like it was 10 degrees warmer?

Believe it or not, it’s not your imagination. It really can feel much warmer in another part of a city, or even another portion of a city street.

Cities, especially urban ones, are often plagued by rising temperatures in the populated metro areas -- an issue most commonly referred to as urban heat islands.

So, what exactly are urban heat islands, and what are their impacts?

Here are some questions (and answers!) all about urban heat islands.

What are urban heat islands?

Heat islands are areas that have higher temperatures than their outlying areas, due to a bigger presence of structures such as buildings and roads that trap the sun’s heat more, according to HARCresearch.org.

As a result, daytime temperatures in some urban areas can be up to 15 degrees higher than temperatures in outlying areas, according to the Environmental Protection Agency.

In some cases, they might even be higher, said Vivek Shandas, a professor in the school of urban studies and planning at Portland State University.

“We’ve found temperature differences across urban neighborhoods to vary by as much as 20 degrees Fahrenheit, due in part to the forms and quality of urban development,” Shandas said. “That can make the difference between life and death for community members who are particularly sensitive to higher temperatures.”

What problems do they cause?

Some of the main issues that urban heat islands cause include the following:

  • Increased energy consumption. With pockets of cities being hotter, it requires more air conditioning in area buildings to make them cooler.
  • Increased emissions of pollutants and gasses. With more air conditioners blasting, that means more electricity is used, which then leads to an increased chance in pollutants and gasses being released from companies that supply electric.
  • Water quality issues. With higher temperatures on pavement or rooftops, stormwater runoff from those areas can, in turn, be higher. When that gets into streams, rivers, ponds or lakes, that can change the water temperature and affect the metabolism of aquatic life and their ecosystems. Such water that has increased bacteria in it can also seep into backyards, which can cause harm to household pets.
  • Enhanced risk of heat-related illness. Whether it’s heat stroke or exhaustion, urban heat islands can be a hindrance to a person’s health. “The phenomena of extreme heat kills more people than any other natural hazard annually, and in cities, we’ve built landscapes that amplify heat, making the temperatures fatal for human health,” Shandas said.

What are some solutions?

Aware of the problem urban heat islands can have on cities, officials, scientists and environmentalists feel there are some ways to combat the issue.

  • Planting trees. Having more trees in urban areas can help shade streets, and thus, keep them cooler. Shaded surfaces can be 20 to 45 degrees cooler than unshaded areas, according to the EPA.
  • Increased green spaces. Having more grass and vegetation not only keeps an area cooler, but it also absorbs rain and floodwaters better.
  • De-paving. This is where pavement, such as in parking lots or on streets, is removed.
  • New pavement coating. Cities are exploring ways to coat the streets of warmer areas with paving materials that better reflect the sun’s rays and are better with water evaporation.
  • New roof materials. Similar to coating streets with material that can lead to cooling, using roofing products that do the same has become more common. Known as a “cool roof,” these reflect sunlight and heat away from a building. Another option is what’s known as a “green roof,” which is a vegetative layer grown on a rooftop that removes heat from the air. Green roofs can be 30 to 40 degrees lower than conventional roofs, according to the EPA.

The above solutions can tend to be more long-term, but Shandas said there can be other short-term solutions, as well.

“These short-terms strategies can come in the form of distributing heat pumps — which are very efficient air conditioners — for individual residences combined with energy assistance programs, and also working with community-based organizations to open cooling centers where residents can remain cool through the day and night,” Shandas said.

Without some of these solutions, you can see below how the average temperature Is predicted to rise (in Houston, for example).


Climate Central graphic (Climate Central)
Climate Central graphic (Climate Central)
Climate Central graphic (Climate Central)
Climate Central graphic (Climate Central)
Climate Central graphic (Climate Central)
Climate Central graphic (Climate Central)

About the Authors:

Keith is a member of Graham Media Group's Digital Content Team, which produces content for all the company's news websites.

Dawn is a Digital Content Editor who has been with Graham Media Group since April 2013. She graduated from Texas State University with a degree in electronic media.