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The Gap Year Blog

The Urban Heat Island Effect - What Is It?

22 Nov 2017 16:45 PM

The temperature of urban areas is becoming a concern. They experience considerably warmer temperatures than surrounding areas. This is the Urban Heat Island Effect. Have you ever wondered why the biggest metropolitan cities such as London, Paris and New York are hotter during the summer?

Well it’s owed to the heat emitted from buildings, cars, busses and even the movement of people! Here we explore the implications of the Urban Heat Island Effect and why it is a concern for the busiest cities.

Why does the Urban Heat Island Effect happen?

First of all, cities are overwhelmingly populated. To be precise; they are home to 3 billion people! But what effect does this have on temperature? Well, the amount of buildings, roads and carparks in cities is forcing out vegetated areas, which act as cooling mechanisms. A city essentially replaces vegetation with buildings, unfortunately losing all cooling capabilities. Urban infrastructure absorbs a considerable amount of light and subsequently emits thermal energy (heat). Due to the fact cities are pretty much made of man-made surfaces; they heat up and hold heat in for longer. This can resemble wearing black on a hot day; black emits more heat, so you will feel hotter!

Photo Credit: Flickr | Giuseppe Carrieri

So why is it bad?

Cities and heatwaves are two things which don’t go well together. Have you ever been walking around London in the height of the summer and find it impossible to cool down? It’s not pleasant. Urban Heat Islands are becoming a modern ecological problem and noticeable in large cities. It’s basically local climate change.

When it comes to dealing with elevated temperatures, especially in the summer, there are several negative impacts that follow. One of which is increased energy consumption; when people get hot, there is demand for cooling such as air conditioning. Joseph Sailor’s research in 2002 showed that the electricity demand compensating for the heat effect increases up to 2% for every 0.6 °C temperature increase. Due to the fact electrical companies tend to rely on fossil fuelled plants, there is a knock on effect for elevated emissions and greenhouse gases, two important ingredients for Climate Change!

In terms of elevated air pollution, there can be negative effects on public health such as asthma, heat stroke and dehydration. In fact, Toronto is an example where heat related illnesses are dramatically high. Statistics show that there are approximately 120 deaths per year related to heatwaves. This is quite shocking!

Photo Credit: Flickr | Henning Klokkeråsen

When it comes to Climate Change and the Urban Heat Island Effect, there is complexity about which causes which. However, the two common explanations seem valid.  The first is that the Urban Heat Island effect is exaggerating climate change by contributing to global temperature changes. The second is that climate change is worsening it. The latter is less justified due to the fact that man-made infrastructure and lack of vegetation in cities has a bigger effect on temperature.

Where is the biggest Urban Heat Island?

New York City, or should I say ‘floating oven’, is the perfect example of a heat island. There has been much research into the temperatures of different land uses around the city to see if there are differences. As you can imagine, Manhattan, Queens and Brooklyn, areas with the most buildings, show the highest temperatures. This really does justify the capability of urban infrastructure emitting and trapping heat!

Photo Credit: Flickr | Andreas Komodromos

Can we reduce it?

A question many people wonder is: ‘how do we make cities more habitable under the Urban Heat Island Effect?’ Well, as we understand, dark, heat-generating surfaces in urban areas are the predominant cause for temperature increase, so the key is changing surface materials. A popular technique, now used in many metropolitan areas, is the concept of green roofing. Green roofs are essentially covered in different types of vegetation and soils to help regain cooling effects of a once natural environment. Stuart Gaffin, who has undertaken many temperature models for New York City, found that green and lighter coloured roofs on buildings could reduce the city’s temperature by 0.67 °C. This might not sound like a lot, but could have a massive impact for power usage, as according to Gaffin, demand for air conditioning is sensitive to tiny variations in temperature. Now you know why people feel cooler wearing light coloured clothing in the summer!

Well there you have it, everything you need to know about the Urban Heat Island effect. If you have never noticed it, next time you’re in a major city in the midst of the summer, think about how much hotter it is. It’s clear that a lot needs to be done in cities to ‘cool’ them down, and green roofs are a good starting point!

By Sophia-Harri Nicholaou - Online Journalism Intern

Frontier runs terrestrial & marine conservation, community, teaching and adventure projects in over 50 countries - join us and explore the world!