urban heat islands

What Are Urban Heat Islands and How to Prevent Them

Rachel Lark - October 12, 2023

We are reader-supported. When you buy through links on our site, we may earn affiliate commission.

Look at many metro areas from a distance on a warm day, and you’ll notice a dome-like atmospheric appearance surrounding the city. It represents more than particulate pollution — it may also indicate temperature changes. Buildings and other structures absorb and re-emit the sun’s heat more than natural landscapes, resulting in urban heat islands. 

Urban heat islands raise inner city temperatures above those in surrounding suburbs and rural areas. They affect human and animal life, creating dangerous conditions and contributing to deaths from extreme temperatures, especially among older and disabled citizens who lack the resources to flee or cool down. 

Preventing and remedying urban heat islands is an urgent environmental goal, as climate change impacts every aspect of human life. Here’s a closer look at the causes of urban heat islands and how smart city planning can address them. 

What Causes Urban Heat Islands? 

A primary cause of urban heat islands is the built environment. Many materials traditionally used in urban buildings absorb and reflect enormous heat. For example, asphalt reflects roughly twice as much heat as grass in mid-afternoon when temperatures soar. It’s hard to be homeless anywhere, but especially in places like Phoenix, AZ, where the sidewalk literally burns people, sending them to hospitals. 

Other causes of urban heat islands include: 

  • City shape: Tall buildings concentrate real estate per square foot but reduce wind speeds needed for cooling residents. Cities with a high density of tall buildings increase the heat island effect.
  • Lack of vegetation: The more built things you have per square foot of space, the less room there is for living, organic plant matter, which is necessary for absorbing carbon dioxide and releasing oxygen while cooling temperatures. 
  • Urban haze: The smog hanging over many cities creates a miniature greenhouse effect, trapping heat inside. 
  • Fossil fuels: Burning oil and coal for gasoline and heat raises temperatures. 

1. How Hot Do Urban Heat Islands Get? 

According to the EPA, urban heat islands raise temperatures by an average of 1° to 7° Fahrenheit. However, they can soar up to 15° to 20° Fahrenheit higher during the worst part of the afternoon. 

2. What’s the Effect of Urban Heat Islands on Human Health? 

Excessive heat can kill. People who live in urban heat islands run higher risks of heat-related illnesses like heat exhaustion and heat stroke. 

However, living for prolonged periods over rising temperatures can have other effects. Recent research from The Lancet shows that each 1° Celsius increase in temperature corresponds to a 2.1% increased risk of cardiovascular disease. Heart disease already kills more men and women worldwide than any other injury or illness. 

Urban heat islands may even wreak havoc on your mental health. Studies suggest increased environmental heat contributes to the following: 

  • Increased oxidative stress on the brain: This may damage mitochondria in nerve cells and the brain’s protective barrier. 
  • Increased brain inflammation: Inflammation plays a role in several mental health conditions, from anxiety to Alzheimer’s. 
  • Excitotoxicity: Occurs when your brain creates too much glutamate, which makes it difficult to relax and contributes to anxiety. 

3. Are Urban Heat Islands Reversible? 

Urban heat islands are clearly bad news. Are they reversible? The answer, fortunately, is yes, but it takes time. However, the pandemic showed that some changes work relatively quickly if people pull together and cooperate. 

4 Techniques for Preventing and Remedying Urban Heat Islands

Here are four techniques to prevent urban heat islands and remedy existing ones. City planners should consider these principles when approving projects and investing funding to make life safer and cooler for all residents. 

1. Better Roofs

Architects can design city roofs to combat urban heat islands in several ways. One such method is cool roofing, which entails a color switch and the right materials. 

However, this approach offers considerable hope. According to estimates from the Lawrence Berkeley National Laboratory, if all North American cities with populations greater than One million adopted cool roofing technologies, it would prevent 57 billion tons of carbon dioxide emissions. 

Another idea is green roofs. As the name implies, such design transforms typical rooftops into urban agricultural centers, complete with fruit trees. Farm-to-table restaurants love such strategies for getting fresh foods for their kitchens, and community gardens atop residential buildings could encourage better relations among neighbors. 

2. Increasing Green Spaces

Another method of preventing and reversing urban heat is to increase available green spaces. More parks and room for growing things aren’t only good for attracting birds and giving kiddos a place to play. Access to the outdoors is also crucial for adult mental health, and adding more such areas throughout urban design creates a win for everyone. 

Cities in China, where urban growth has hit hardest, have done a fabulous job incorporating green spaces into city planning. Areas like Hangzhou feature a maze of walking and bike paths around green places with plenty of trees and foliage. The attention to making alternative transportation feasible reduces the urban heat island effect while encouraging residents to stay healthy. 

3. Use Green Irrigation Practices

Adding more plants to cityscapes matters, but they should be the right varieties. City planners should gravitate to native species that require little irrigation to stay green. Furthermore, improvements in graywater waste management treatments can make new use of what runs down sink drains. 

Green irrigation works hand in hand with greener building practices. For example, green buildings can incorporate living walls that use a recirculating irrigation system to prevent needing water from an external source. 

4. Reduce Traffic 

Reducing traffic is an often overlooked way to reduce heat islands. Traffic concentrates in cities, and long lines of idling cars produce countless emissions, contributing to the smog that traps warmth within the dome. 

One method of reducing traffic is to make public and alternative transportation more accessible. Electric buses are great — but only if they run when and where people need to go. Light rail systems can share room with city streets to reduce passenger car traffic while facilitating downtown excursions. 

Furthermore, many urban landscapes aren’t ideal for biking, although it’s among the most sustainable transportation methods. Installing lanes complete with rumble strips or dividers keeps cyclers safe. When paired with an e-bike share program, cities can reduce emissions while encouraging residents to get moving, improving overall health. 

Preventing and Remedying Urban Heat Islands

Urban heat poses a threat to human health. They also make city life unbearable in the summer. Fortunately, taking the correct steps can remedy and prevent these issues. 

City planners should consider the approaches above to minimize heat islands. Doing so protects the health of residents, combats climate change and makes their destination more pleasant for visitors and inhabitants alike. 

Share on

Like what you read? Join other Environment.co readers!

Get the latest updates on our planet by subscribing to the Environment.co newsletter!

About the author

Rachel Lark

Rachel serves as the Assistant Editor of Environment.co. A true foodie and activist at heart, she loves covering topics ranging from veganism to off grid living.