Urban Heat Island Effect and How Cities Manage It
2020 was named the hottest year on record and the coming years are on track to get warmer. Compared to the countryside, cities have often taken more heat - why is that?
Illustration and Animation by Marian Femenias-Moratinos.
Anyone who has been in London during the summertime knows the unbearable mugginess and heat that the city holds. Londoners saunter from the shelter of one beer garden to another, tourists fill up the limited green spaces with cool beverages and ridiculous sun hats, and everybody is justifiably wearing half nothing as if they were in Ibiza. Unlike the coastal regions, where people can at least enjoy the occasional breeze, summertime city heat can feel claustrophobic and inescapable. With over half of the world’s population living in urban areas, and urban development growing at an alarming rate, it’s crucial to understand what exactly is causing this heat, how it effects urban populations, and what some of the green solutions are.
So, why are cities so prone to overheating? This phenomenon is called the Urban Heat Island (UHI) effect. The UHI effect is the cumulative result of cities absorbing and retaining heat – typically at a higher rate than in rural areas. There are several contributing factors. The first is obvious: there are more people in cities and therefore more activity. This means more vehicles emitting hot exhaust fumes, more energy being used for more buildings, and more crowds packed into restaurants, museums or transportation. Another factor that contributes to the UHI effect is something called the albedo level, which measures how reflective a surface is. For instance, the polar ice caps have an extremely high albedo level since their white surfaces are excellent at reflecting the sun’s radiation back into space. Hence, the ice sheets and glaciers around the world act as a cooling system for our planet. Cities, on the other hand, are typically dark concrete jungles, which have a very low albedo level. The darker roads and buildings absorb and retain heat extremely well, turning a city into an enormous sauna. The UHI effect is also created by the serious lack of vegetation in cities. Trees provide shelter from the sun, shading the ground and decreasing surface temperatures in the process. Vegetation uses the sun’s light and carbon dioxide for photosynthesis, contributing to our ecosystems. When building or expanding cities, massive amounts of forests are torn down, only to be replaced with dark concrete which absorbs heat and contributes negatively to our environment.
The consequences of the UHI effect are far reaching. Not only is it environmentally damaging, it also causes a huge health impact which disproportionately affects those in lower socio-economic groups. The many health effects of living in a city subject to the UHI effect include: increased heat stroke, exhaustion, respiratory issues, heat cramps, headaches, heat-related mortality and general discomfort. The disproportionate health effects on different social groups can be measured by recent studies. In a 2018 study examining the impacts of increased temperatures on exam performance by students in the US, the findings showed that higher temperatures led to worse results. Trying to focus on revision during heatwaves is obviously a challenge. However, the study also found that low income schools were more gravely affected by this due to a lack of access to sufficient air conditioning. The same concept can be applied to lower income households, where residents experience “elevated heat exposure”. On top of this, anyone who does manual work, such as construction, is directly exposed to these conditions and therefore more at risk of heatstroke or other related illnesses.
As a result, the UHI effect leads to an increased use of energy as city residents turn up their aircon to cope with the extreme conditions, leading to increased emissions. The EPA examined a number of studies across several countries, finding that “electricity demand for air conditioning increased approximately 1–9% for each 2°F increase in temperature.” In a world where we are trying desperately to decrease our consumption of energy, this feels like a serious step back into a vicious cycle. On top of this, the increased temperatures impact city animals who are not used to the unnatural extremes in climate. The heat leads to a decreased access to food, shelter and water for the creatures that are already working hard to adapt to an increasingly unnatural world.
On the bright side, there are many solutions to this problem - some of them extraordinarily simple. One such technique for combating the UHI effect is the simple idea of painting dark roads and buildings a lighter colour, increasing its reflectivity in the process. New York City implemented this strategy under a program called NYC CoolRoofs. The program, which was launched in 2009, coated 626 buildings with a white coating, spanning over 5.7 million square feet of rooftop. This directly helped with cooling down the metropolis, reducing cooling costs by 10-30% for the building owners. The company Guardtop, a road sealcoat producer, uses a water-based, asphalt emulsion sealcoat to make roads lighter and more reflective. This simple act can reduce surface temperatures by roughly 10-30 degrees Fahrenheit. Such a small change, which requires very little investment in the grand scheme of things, could have significant results.
Thankfully, the world view towards climate change is evolving, and cities are gradually appreciating the ecological, economic and social value of green infrastructure. Prioritising, protecting and investing in green infrastructure is an absolute must if we hope to build a sustainable world. The new “forest town” Tengah, in Singapore is currently under construction and provides a blueprint for how to firmly place nature at the core of urban areas. Its five districts are bursting with nature, from forest corridors, which join the residential areas, to farmways that encourage community gardening and farmers markets. This town will prioritise green spaces at every step of its construction. Singapore itself boasts the reputation as one of the greenest cities in the world. Roughly 46% of the land was occupied by green space in 2020, with a “tree canopy percentage of nearly 30%”. The benefits of prioritising nature in your city go way beyond tackling the UHI effect. Trees contribute to air quality by absorbing CO2, they combat noise pollution by acting as a barrier between busy streets and houses or parks, and have been shown time and time again to boost mental health. Not to mention that they provide food and shelter to wildlife, offering refuge to desperately threatened biodiversity. Adding vegetation to our cities, be it through rooftop gardens, vertical gardens, parks or lining the streets, is a sure way of creating a healthier and more beautiful city.
The final and central solution to the problem of cities overheating are its residents. Consumption on a large scale is the biggest threat to our world’s environment. Be it plastic, food waste or emissions, we are consuming too much with too little responsibility or accountability. An effective way of tackling the UHI effect and cooling city temperatures is to reduce our energy use. The aforementioned sustainable town, Tengah, is also a smart town. Smart homes allow residents to track their personal energy use, helping them to see where they can make reductions. This not only saves in lowered emissions but also saves the residents in energy costs. The other key way that we can reduce emissions in a city, and subsequently the UHI effect, is by transforming our transportation systems. Moving toward a car-free city tackles one of the biggest contributions to city emissions. And, as is typical of sustainability solutions, this has various benefits that go beyond the environment. Swapping out buses and taxis for electric alternatives, creating car-free zones, and investing into cycle lanes and pedestrian areas can significantly drop emissions levels. This contributes to improving the air quality, which aids the respiratory health of locals. City residents’ health also benefits from the encouraged use of bicycles and walking instead of driving. Some cities that have removed motor vehicles from parts of their city experienced an economic boost thereafter, finding that it significantly increased pedestrian activity. The Exeter City Council found a 30% increase in footfall between 2002 and 2010 in the shopping areas where motor vehicles were removed. In a globalised world where small businesses are struggling to compete with conglomerates like Amazon, this would be a big win for local entrepreneurs and communities.
However, as is often the case with climate change, the issue is not finding the solutions but in implementing them. The truth of the matter is that we have all the tools we need in our sustainability toolbox to make cities greener, we are simply not using them as much as we could. There are a million delightful and innovative ways of making a city greener, but it is up to individuals, local councils and governments to implement and invest in these techniques. Otherwise, they risk remaining clever ideas.
Georgie Power
Georgie Power recently completed an MSc in Climate Change in Dublin City University, studying the environmental, economic, political and social implications of climate change. In working with the Carbon Disclosure Project, helping companies around the world manage and report their carbon emissions, she learned of the role that corporations have in the transition to a sustainable and ethical economy. Now, she works as a climate change author, focusing on her passions for sharing solution-based information for environmental issues and the social, political and economic influences they have on our world.
You can find more of her work on Instagram @easy.beinggreen.