Urban Heat Island, or UHI in short, is an area is have much warmer than other areas around it. In fact, we have numberless UHI areas around the globe; many cities we know are UHI areas. The maps below show some of known cities that already became UHI areas:
Image Source: https://images.app.goo.gl/cdvULJEpSsfkZXGj6
From the maps we can see that average temperatures that are higher near the center of the cities and airport locations also suffered the UHI effects. Those places suffered by the UHI effects, always come with a higher population of industrial activities (“Urban Heat Island”). Not only cities in Europe, but most big cities in the US also have the same situation as the cities located above.
Urban areas are always concentrated with a large population; more people means more carbon dioxide output because a human’s breath consumes oxygen and produces carbon dioxide, and more people living in areas with more carbon dioxide. Carbon dioxide is one of the well-known greenhouse gases; therefore, it would make the area be impacted by the greenhouse gas effects worse than other areas. Second, urban areas have less vegetation. Plants are one of the major producers of oxygen and they are also consumers of carbon dioxide; less vegetation within the urban area could make a lower transfer rate between oxygen and carbon dioxide.
The high production rate of carbon dioxide and the lower CO2-O2 transfer rate would increase the amount of carbon dioxide in urban areas. And last, but not least, urban areas have a lot of buildings; these buildings are concentrated within the area and they would act like a wind wall. The wind flowing from outside of the city would be mostly blocked by buildings, which makes the air flowing within the urban area become slower. The concentrated greenhouse gases can’t be released outside of the city.
Let’s imagine the city as a roaster. Buildings are like a thermal barrier of a roaster; the sun is like the heat lighter of a roaster; sunshine increases the temperature within the city; and the buildings keep the rest of the heat within the city. When this situation kept going for long period of time, the different temperatures between urban areas and other places would get higher, making the urban areas have the worst influence by greenhouse gas effects.
In fact, due to a study by the United States Environment Protection Agency (USEPA), the risk of heat stroke and other heat related diseases in urban areas are higher than the countryside. Also, extreme hot summers and warmer winters often occur in urban areas (“Climate and Health Assessment”). For example, in NYC, we have already experienced a warmer winter between 2019 and 2020; we have a winter with less snow than usual from last year. If we don’t find a way to stop the UHI effects in our city, we may experience warmer winters and extreme hot summer weathers in the future.
Nova, Joanne. “So hot that we can see those Urban Heat Islands from space.” JoNova, 2020, http://joannenova.com.au/2019/08/we-can-see-the-urban-heat-islands-from-space/. Accessed 15 May 2020.
“Urban Heat Island.” National Geographic, National Geographic Society, 2020, https://www.nationalgeographic.org/encyclopedia/urban-heat-island/. Accessed 15 May 2020.
“Climate and Health Assessment.” Global Change. US Global Change Research Program, 2020, https://health2016.globalchange.gov/temperature-related-death-and-illness. Accessed 15 May 2020
Urban Heat Islands can be controlled to a degree. Utilizing green roofs, creating more vegetation, more permeable pavements, and using higher albedo materials for roofs and pavements can all work towards decreasing the heat and energy waste caused by UHI’s. Enacting some of these changes with increased work towards lower carbon emissions, in general, will continue to further reduce the carbon footprint that produces UHI’s. Some things however are always going to create UHI’s. In their nature a UHI is an area that absorbs a lot of a heat mass, buildings primarily cause this to happen. Due to the nature of cities and urban areas it is impossible to take away the mass entirely, but offsetting it is a possibility.
Green roofs help to increase vegetation of the urban area which can attribute to the recycling of carbon emissions into oxygen. While this does not get rid of the heat as well as some of the other methods described it does offset the carbon emissions caused by inefficient energy use. The absorption of the greenhouse gases not only removes them but replaces them with oxygen helping to alleviate smog-like conditions in some cities. It also cools the air around the building itself. Depending on the plants used, they may produce shade to the surrounding area too. Which can also be done by planting more vegetation where possible. Whether lining a parking lot or on sidewalks, vegetation itself, trees specifically, can create shade that will cool the area and absorb the heat instead of holding it in as the sidewalk and streets do. However, an alternative to this is to create roofs that have a high albedo, by using materials other than dark paints, or asphalt. This will help to reflect most of the sun’s radiation back out to space instead of getting trapped and then radiated out of the building itself. This can also be applied down to the street and sidewalk, and some materials can even achieve high albedo without needing to be completely reflective of the light itself. Streets themselves can also be altered to become more permeable, thus allowing water to seep in and cool down the soil that lies underneath. As most urban areas are constructed today streets are made of non-permeable low albedo materials, and water is often redirected to storm drains and sewage systems that take the hot water and push it out to rivers and lakes, further decreasing diversity of wildlife and attributing to hotter temperatures elsewhere.
As you can see, UHI’s are a big problem but they can be fixed. With the right tools and some key changes in small everyday things UHI’s effects can be reduced to the point that they aren’t as big of a problem and we can start to set right what lasting effect our urbanization has had on the environment.