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The Urban Heat Island Effect

Have you ever wondered why city centres are sometimes bleak and grey while at the same time, surrounding neighbourhoods and the countryside are covered in a stunning layer of fresh white snow? Or when you decide to visit a city while coming from a rural place, it seems hotter than before? The chances are that this is not just your imagination, but an actual phenomenon.

Your observation is known as the ‘urban heat island effect’, a direct and often unwanted result of urbanisation. An urban heat island is a place with a large surface area of ‘dark’ materials such as asphalt, pavement and roofs. A city centre, for example, then results in a higher atmospheric temperature since this place absorbs and retains heat much more than natural elements like trees and water. Furthermore, buildings experience a lower heat loss due to lower wind speeds in cities, and extra heat is produced by human activities like the heating of houses and the traffic in a city.

A graphic depiction of the temperature profile of a city, clearly demonstrating the Urban Heat Island effect. Source: Wikimedia Commons

As the name states, the urban heat island effect results in higher temperatures in built-up areas, which then impact the liveability of these urban places. Not only do mainly vulnerable people, often the elderly, experience heat stress which leads to increased mortality, the higher temperature also leads to a decreased lifespan of structures. Moreover, the heat negatively impacts the ecosystems present in cities. Thus, in order to sustain liveable urban centres, the urban heat island effect is one of the problems that should be addressed.

Fortunately, there are plenty of solutions that can be deployed to cool city centres a bit down again. Large trees do not only provide shade on otherwise sunbathing streets and squares, but they also create places that people enjoy spending time at. The municipality of Groningen, for example, is trying to implement this in the redesign of the Grote Markt. Furthermore, the creation of water-embracing features like fountains, ponds and pools offer man and nature the possibility to cool down and rehydrate. Additionally, an improvement to the tar-covered roofs in cities can be the installation of green roofs, which help to cool down cities and accidentally also assist with a regulated discharge of precipitation.

A temperature map (top) creating using infrared satellite imagery and a map of the density of vegetation (bottom) in New York City, demonstrating the correlation between cooler temperatures and higher vegetation density. Source: Wikimedia Commons.

Besides these more apparent modifications, some cities do not hesitate to implement more unorthodox implementations to their cities: Los Angeles decided to paint several streets white to limit the energy absorption of the otherwise black asphalt. But some smaller adjustments can already help; creating green parking lots and road dividers and -shoulders, for instance, can all replace concrete or asphalt structures.

Cities are marvellous structures and organisms on their own, but sometimes they should be tamed to increase their benefits for the inhabitants. “How to Sustain Liveable Urban Centers” you ask, keeping control of the urban heat island effect is undoubtedly one important part of the answer.

Thijs van Soest
Thijs van Soest
Hi, I am Thijs! Since September 2018, I have been part of Girugten, and I am the current Chairman of the Editorial Team. I am following the MSc Real Estate Studies. My main interests are infrastructure, transport planning and real estate, but I also write about other subjects.
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