Urban Heat Islands: What Are They and Can We Cool them?

The concept of urban heat islands refers to built areas that are hotter than their neighboring rural areas. The annual mean air temperature of a city with 1 million people or more, for example, can be around 1.8-5.4 degrees F (1-3 degrees C) warmer than its surroundings. In the evening, the difference can be as high as 22 degrees F (12 degrees C). As cities develop, often times horizontally and then vertically, they lose vegetation and go higher and higher, reaching warmer levels of air. Moreover, the ground starts featuring more and more buildings and utilitarian areas (as opposed to green ones). With less shade and moisture, they cannot keep themselves cool anymore.

If you wonder why a city experiences different heat levels than its nearby rural area, the explanation is simple: an urban area’s road surfaces, pavements, and buildings all contribute to keeping such environments three to four degrees hotter than surrounding non-urbanized areas (which, in turn, benefit from more vegetation). Moreover, an urban heat island effect occurs because the dense dark surfaces on roads and building materials used in cities accumulate and store heat during the day and then release it at night. If you live in a crowded city and you wait for the summer night to cool you off, you probably know by now that you do not get much relief because roads and buildings trap heat.

What Leads to the Formation of Urban Heat Islands?

The UHI effect has plenty of causes. Such metropolitan areas are very hot day and night because of an accumulation of factors:

  • The energy created by all the people, cars, buses, and trains active in such areas;
  • Dense urban populations;
  • Houses, shops, and industrial buildings were built close together;
  • Building materials that are very good insulators, trapping heat during the day and emanating it during the night;
  • Building materials’ dark colors: most construction materials are very dark in color, absorbing all wavelengths of light energy and converting them into heat.
  • Waste heat: the heat released by cars, tools, factories, industrial compounds etc.

During the day, all these factors accumulate, leading to the increase of the urban temperature. The heat is trapped in and between buildings, with no cooling relief for the dense population. Cities such as New York, London, Los Angeles or Melbourne are some of the most “suffering” urban conglomerates in the world.

In rural areas, the situation is far more acceptable. You will find there plenty of trees, crops, grasses, vegetation, and irrigation systems that make the air more breathable and definitely cooler. Moreover, besides the shadow and breeze trees and grasses offer, we have to remember that nature’s air conditioning is the plants’ transpiration effect, which makes rural areas desirable places to live.

What Are the Consequences of Urban Heat Islands?

Urban heat islands can affect communities by increasing summertime energy demands and consumption, but also air conditioning costs, air pollution and greenhouse gases emissions, heat-related illness and mortality, and water and water quality.

If we do not forget that one of the main causes leading to the creation of an urban heat island is the density of cars, means of transportation, and factories/plants, industrial compounds, it is easy to figure out that one of the first negative consequences is air pollution. Lower air quality comes as a logical follow-up of a UHI because the air contains more waste products from vehicles, industry, and people. If you remember, we reported the findings of a recent study showing that air pollution may cause fetal brain damage, so the impact of UHI on human health is a serious research topic.

As you can guess, we should all take into account other UHI consequences: increased global warming effects, endangering of animals and aquatic species, propagation of heat-loving illnesses, and more.

What Can We Do to Cool Down Urban Heat Islands?

Luckily, we have all something to do to lower the risks generated by the urban heat islands. Authorities and cities usually implement five recognized methods to limit the negative effects of UHI:

  • Trees and Vegetation Plantation – More parks, roadside trees, and urban vegetation provide shade and cooling, lowering the air temperatures and reducing stormwater runoff.
  • Green Roofs and Gardens – Garden rooftops are not a new idea, but definitely, one that gains popularity. Reducing the temperatures of the roof surface and the surrounding air and improves storm water management, shade provision and heat removal from the air.
  • Cool Roofs – Cool roofs feature materials or coatings that significantly reflect sunlight and heat away from a building. Therefore, they reduce roof temperatures; increase the comfort of occupants, and lower energy demand.
  • Cool Pavements – These unconventional pavements for sidewalks, parking lots, and streets remain cooler than traditional ones by reflecting much more solar energy and enhancing water evaporation. They can cool down the pavement surface and surrounding air, but also reduce stormwater runoff and improve nighttime visibility.
  • Smart Growth – Part of larger development and conservation strategies, smart growth can protect the natural environment and at the same time make communities more attractive, economically stronger, and healthier.

As a community, we can also get involved in reducing the negative impact of urban heat islands. Besides the fact that we can choose smarter and eco-friendlier building materials for our homes, we can also engage in building and managing community gardens. Moreover, we can all make voluntary efforts to build, travel, and live greener and increase awareness within our community and local or national authorities.

  • We can all try to plant more trees and vegetation in our neighborhoods and around our blocks and houses;
  • Use energy-efficient appliances and equipment;
  • Install cool roofs and green roofs;
  • Make sure our friends, children, the elderly, the poor, the homeless, the young, and the sick benefit from cool air or make it to cooling centers to prevent heat-related illnesses and death;
  • Make sure that pets, street animals, and birds get shadow and water during urban heat waves.

If we want to secure a better life for our families and friends and a healthier future for the next generations, we should all become more aware in the relationship with urban heat waves and the means we have to combat them. As usual, lobby, advocacy, and personal examples are the ways to go when it comes to changing the world one green action at a time.

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William E. Eubanks

I'm one of the main writers on the site; mostly dealing with environmental news and ways to live green. My goal is to educate others about this great planet, and the ways we can help to protect it.

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