What Causes the Heat Island Effect? 10 Things (2024) You Have to Know

Do you live in a concrete jungle?

If so, you may suffer from the Heat Island Effect.

Take a moment to think how far away the nearest piece of nature is from your home.

Do you have to drive there?

Is it expansive?

Are more neighborhoods or cities closing in and reducing the size of the natural space?

A large percentage of people live far away from nature.

Instead of open fields, forests, rivers, and lakes, we have concrete and cement.

It’s easy to see that cities don’t do the surrounding environment any good, but there’s another symptom caused by all these roads and buildings.

All that concrete and cement is heating up cities and causing real issues.

We’re going to check out what causes the Heat Island Effect, its impact on people and the environment, and what we can do to stop it.

Let’s go!

1. What is the Heat Island Effect?

The Heat Island Effect is an increase in temperatures in cities due to the infrastructure of urbanized areas absorbing heat from the sun and emitting it into the air.

If you looked through a thermal imaging camera, things like houses, roads, and cars would be glowing red, orange, and yellow as they soak up the heat of the day; however, the natural landscape would be a cool blue and green in comparison.

Big urban cities can see temperature increases up to 7 to 10°F, but there have been even more extreme cases.

In Richmond, Virginia, there was a 16°F difference between the surface temperatures downtown and the surrounding rural areas during a heat wave.

The temperature in the city was 103°F, while the natural area was 87°F.

That’s a massive discrepancy, and events like this are happening all over the country (and the world).

Before we talk about the negative impacts, let’s check out what causes the Heat Island Effect.

2. What Causes the Heat Island Effect?

What causes the heat island effect isn’t just one easily solvable thing–no, no, no!

There are many factors that are to blame, and dealing with them won’t be easy.

bulletUrban Infrastructure

Urban land cover, like parking lots, roads, and sidewalks, use brick, cement, and asphalt, which don’t reflect solar energy.

Instead, these materials soak in the sun’s energy and emit heat into the environment.

The level of waste heat emission is far higher than in natural landscapes.

bulletMinimal Natural Landscapes

Just about everything that makes up a natural landscape is designed to effectively use the sun’s energy.

Trees, for example, not only provide shade but also provide a cooling effect thanks to the sun evaporating water in the leaves.

Bodies of water also provide a cooling effect due to evaporation and have excellent heat retention.

All these factors help keep the environment from reaching dangerous temperatures.

The fewer natural spaces, the hotter the area will be.

bulletCity Layouts

When tall buildings are constructed closely together, it can make releasing heat difficult, leading to even more intense areas of concentrated heat.

Clusters of towers and skyscrapers can also prevent natural wind flow from getting to the area.

bulletHuman Activity

As you may have guessed, human activity also plays a big part in creating heat islands.

Our cars emit a lot of heat in addition to carbon dioxide.

Also, factories and other work plants contribute to a great deal of heat that gets trapped within the city.


Where a city is located plays a big role in causing the Heat Island Effect.

If the local weather is mild, calm, and sunny, the effect is more likely to occur.

If the local weather is cool, overcast, and rainy, the effect is less likely to occur.

3. What Are the Major Impacts?

A severe increase in temperature is no joke and puts people in danger.

Real issues arise in the summer when regular temperatures are already at their peak, and the Heat Island Effect is there to exacerbate it.

These issues include:

bulletIncreased Asthma and Lung Disease in Children

The United States Environmental Protection Agency (EPA) has found that the Heat Island Effect is linked to children experiencing aggravated asthma and lung diseases.

Hotter temperatures usually worsen air quality, and kids, who have smaller bodies and spend time outside playing, are directly impacted.

bulletIncreased Heat-Related Illnesses in Low-Income Communities

Low-income communities have fewer A/C units, more compact living quarters, and a higher homeless population that doesn’t have access to shelter.

All these factors lead to an increase in heat-related illnesses like heat stroke and severe dehydration.

bulletIncreased Heat-Related Illnesses for Outdoor Workers

Outdoor workers are an obvious group that gets hit hard by the Heat Island Effect.

Anyone working in an exposed environment is more susceptible to heat-related illness.

Workers who are outside exerting a lot of energy, like builders, are most at risk.

bulletDecreased Well-Being of the Elderly

When heat waves roll through cities, the elderly are more likely to stay indoors, which can impact their physical and mental health.

EPA has found evidence that older people become less mobile and more isolated, decreasing overall well-being.

bulletDecreased Health of Sick People

People who already have challenging health issues, including chronic diseases and physical disabilities, may experience worse symptoms.

Heat causes the heart to work harder, blood pressure to drop, and the body to exert more energy, which is not ideal for someone with poor health.

4. How Can We Prevent Heat Islands?

Heat islands are a big issue and an intimidating one when looking at all the factors that contribute to them.

Well, the good news is that there are things that can be done, and some cities are taking proactive steps to minimize the Heat Island Effect.

bulletPlant Trees

Trees are a wonderful source of shade that keeps the ground beneath them cool and gives people refuge from the heat.

They also have a natural cooling effect when the sun evaporates water from the leaves.

More trees, fewer problems!

bulletCreate Shaded Structures

In addition to planting more trees, cities, neighborhoods, and homeowners can create more shaded structures.

Take the street in Agueda, Portugal, for example.

The street and the pedestrians are protected from the sun by a roof made of umbrellas.

It’s a fun, creative way to fight against the Heat Island Effect.

bulletInstall Green Roofing

Green roofing isn’t just a roof painted green.

It’s actually a roof made of vegetation.

Because plants don’t emit as much heat as unnatural materials, it’s a great way to stabilize the temperatures of a concrete jungle.

An example of this can be seen at the Chicago City Hall building, which is part of EPA’s study to understand its impact.

bulletPaint Walls and Roofs White

Dark colors absorb more heat than light colors.

You’ve probably experienced this if you got stuck in a black shirt on a blazing hot day.

Painting the walls and roofs white will help decrease the amount of heat buildings absorb.

bulletRedesign City Layouts

Cities aren’t designed to encourage airflow or prevent areas of concentrated heat.

It’s unrealistic to completely redesign city layouts, but we can take small steps and keep what causes the Heat Island Effect in mind when we’re building new cities.

5. When Did Urban Heat Islands Start?

The Heat Island Effect was first detected by Luke Howard, a chemist and meteorologist, in 1810.

Howard noticed that the city of London was a few degrees warmer than the surrounding countryside nearby.

Although Howard was the first to detect the Heat Island Effect, he wasn’t the one who named it.

A German meteorologist named Albert Peppler is believed to be the first to use the term in 1929.

There’s no way to say when exactly the first heat island occurred, but we can definitely make a connection between the industrial revolution and the Heat Island Effect.

As you can imagine, cities today have many more roads, buildings, automobiles, and pollution, so it’s no surprise that the severity has increased as well.

6. Do Heat Islands Contribute to Global Warming?

Heat islands are likely contributing to global warming (or climate change as a whole), even if just by a small amount.

NASA has said that heat islands don’t contribute to global warming nearly as much as the burning of fossil fuels.

With that being said, when the temperatures of a city increase, more people use their A/C units, which requires more electricity and the burning of fossil fuels.

As you well know, when fossil fuels are burned, it results in the greenhouse gas effect.

So, heat islands are definitely not helping the issue of global warming.

7. Can Urban Heat Islands Cause Storms?

Heat islands are already vulnerable to the impact of increased temperatures, but does the effect cause storms?

Lightning storms favor hot weather–think of summers in the south, for example.

After heat waves, the air closer to the ground is warmer than the air above it, which is considered to be unstable.

As the warm air rises, it mixes with the cooler air, creating negative electrons.

The Earth has a positive charge, and when the difference between positive and negative grows strong enough, there will be an electrical release–lightning.

Lightning storms can be extremely dangerous and damage power sources.

Because heat islands aren’t known to severely impact the overall global temperature, as of now, they don’t increase the chances of natural disasters; however, as cities expand and more pop up around the world, it could be a contributing factor to dangerous natural events.

8. How Do Heat Islands Affect Water Quality?

The Heat Island Effect can have detrimental effects on local water quality.

Increased use of air conditioning leads to more air pollution, which leads to acid rain.

Acid rain is acidic, which does damage to the health of plants, animals, and humans and causes more weathering to infrastructure than normal rainfall.

The acidic water can also flow into natural bodies of water, disrupting the local ecosystem.

But that’s not all.

When rain falls onto a heat island, it warms up drastically as it runs across hot surfaces.

That hot water then flows into sewers, rivers, and streams.

The increased water temperature can cause stress to marine life that is used to cooler temperatures.

Acid rain also permeates harmful chemicals into the air, nitric and sulfuric acid, which can lead to respiratory diseases and irritation.

9. What U.S. Cities Are Affected?

Not all cities suffer from the Heat Island Effect–or at least not enough to be considered a heat island.

But the United States is home to dozens of destinations with significantly higher temperatures than outside the city limits.

Let’s take a look at the top five heat islands and what’s causing the effect.

bulletNew Orleans (8.94°F)

bulletNewark (7.71°F)

bulletNew York City (7.62°F)

bulletHouston (7.46°F)

bulletSan Francisco (7.37°F)

The primary causes of these heat islands are impermeable surfaces (concrete, cement, asphalt, etc.), building height, population density, and albedo (the solar radiation absorbed by objects).

New York City and Houston are two of the most populated cities in the country, and several other major cities are in the top 20 of the most severe heat islands.

A large percentage of people in the United States are living in heat islands, and they’re suffering the consequences even if they don’t know it.

10. How Does The Urban Heat Island Effect Affect Daytime vs. Nighttime Temperatures?

The Heat Island Effect can be felt during the day and night.

Do you think the temperature difference between the city and the surrounding area is greatest during the daytime or nighttime?

If you answered nighttime…you are correct!

The biggest difference in temperatures can usually be seen towards the evening.

It’s difficult for all the objects and materials of a city to release the absorbed heat in an environment that’s equally as hot.

Of course, temperatures will drop when the sun goes down, but there are only so many hours before the sun is up again, and the Heat Island Effect continues.

If you live near a city, you could do an experiment by driving downtown, checking the temperature, and driving out of town to compare.

Final Thoughts

The next time you’re in a big city, count how many trees you see and check if there are any green spaces nearby.

Now that you know what causes the Heat Island Effect, you’ll forever look at big, urbanized areas in a new way.

Unless cities begin installing green roofs, planting trees, and building more shaded structures, they’re just going to keep getting hotter and hotter.

As you saw with the City Hall building in Chicago, the government, on a state and federal level, is beginning to address the problem.

But, as of now, heat islands don’t appear to be on the top of the to-do list.

Luckily, you can make your own home a cool oasis on the heat island by having lots of vegetation around and shaded areas.

If you live in one of the top heat islands, stay safe and consider starting a community project!

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Erika Gokce Capital

Disclaimer: we are not lawyers, accountants or financial advisors and the information in this article is for informational purposes only. This article is based on our own research and experience and we do our best to keep it accurate and up-to-date, but it may contain errors. Please be sure to consult a legal or financial professional before making any investment decisions.


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