Back in April, a 15-day heatwave wreaked havoc across South-East Asia, with temperatures soaring to over 40ºC in some areas. The relentless heat forced the closure of schools, decimated agricultural yields, and compelled governments to issue urgent health warnings. This extreme weather event, known as the ‘urban heat island’ effect, primarily occurs in urban areas where temperatures are higher than in surrounding regions.
Even in a country as small as Singapore, some parts of the island can get hotter (and wetter) than others. For example, in July 2021, Singapore’s temperatures soared above 34ºC for 2 weeks, but according to reports, the eastern parts have consistently seen higher temperatures than the rest of the island. Whenever it gets hot in Singapore, the east side seems to suffer the most – as much as 4ºC hotter. This is because it has more buildings and roads than green areas (studies show that urban and green areas in Singapore can have differences of up to 7ºC)!
By understanding the causes of this intense heat, we can develop effective solutions to address it. Here are some factors causing the urban heat island effect:
Concrete buildings and pavements
In cities, heat is trapped between tall buildings and pavements, because materials such as concrete, bricks, and tiles have high thermal mass. This means they absorb and store a lot of heat – to the tune of one kilowatt per square metre! In face, concrete is capable of absorbing as much as 95% of the sun’s energy, which is then radiated back into the surrounding atmosphere. And yes, it releases the heat well into the night.
This doesn’t really bode well for Singapore – not only do we have a lot of pavements, we also have a lot of construction sites. And they all use a lot of concrete. It’s no wonder we’re feeling the heat.
Solution: While it’s not feasible to build skyscrapers with materials like wood, there are ways to reduce the reflected heat. Buildings can be painted with special pigments designed to reflect solar radiation, which can reduce surface temperatures by more than 10°C, compared to conventional paint. When it comes to concrete sidewalks, shielding them from the sun is essential: plant trees that provide shade or construct covered walkways.
Asphalt Roads
Stand next to a road on a blazing hot day and you’ll feel how hot asphalt can be. We all know that dark materials absorb light and convert it to heat – just touch your own head after a few minutes in the sun.
Asphalt surfaces can be anywhere from 4-15ºC hotter than the surrounding surfaces during the day. It’s bombarded not only with heat from the sun, but also UV rays. Asphalt’s dark colour absorbs sunlight and releases it slowly, while concrete’s lighter colour reflects it which is why we’re feeling this urban heat heat day and night.
In addition to the hot road, cars travelling on those roads also contribute to the heat. A moving car burns up fuel that’s converted into heat, either directly via the heat of the motor, or the heated exhaust gas. Not to mention there’s heat through the air friction and moving tyres. Car windows absorb a lot of heat, which means everyone turns on their aircons, which translates to more heat being produced.
Solution: Since it’s the dark colour of asphalt that’s absorbing heat, some cities are experimenting with lighter-coloured asphalt. While it’s cooled the road down by up to 8ºC, there’s no concrete evidence that it’s cooling down the ambient air temperature. The easier solution for Singapore is this: get more people to use MRTs.
Glass and steel towers
Just head to the CBD or financial district, and you’ll see soaring glass-and-steel skyscrapers everywhere you look. These glass surfaces are also sources of heat – but not so much for the occupants inside, because the glasses are specially coated to prevent heat from entering. However, the heat reflects back onto its surroundings, and the pavement below (which, as you remember, is made of concrete which absorbs a ton of heat).
Of course another reason it gets so hot in the city is because so many tall buildings are packed tightly together, it prevents airflow.
Solution: Shading the ground with manmade structures or trees would help lower the temperature, but a better solution would be to relook at the idea of fully glass-and-steel skyscrapers. Instead of tall, skinny buildings, the form could be changed to a sphere, or an octagon, which are more efficient. Another solution is to build green roofs with plants.
Solar radiation
Singapore sits near the equator, which means we – along with every tropical country – typically receive the highest solar radiation levels (welcome to the jungle!). This means that cities in the tropics will tend to be hotter not just because of solar radiation, but the evaporation is greater than on most areas on earth. The result is high humidity. So, heat + humidity = super uncomfortably hot.
Solution: Sadly, there’s nothing we can do about our geographical position on earth. However, some researchers want to cool the earth by reflecting sunlight back into space! ‘Solar radiation modification‘ could theoretically cool down the earth by reflecting sunlight back into space – one method literally injects aerosols into the stratosphere to reflect sunlight away from the planet. Only time will tell if it’ll actually come to fruition.
The best solution for every city? Planting trees. Multiple studies have shown that trees – more than grass or shrubs – can lower ambient temperature by up to 12ºC. Not only do they provide shade from the sun’s hot UV rays, it also actively cools the environment down via evapotranspiration, which uses heat from the air to evaporate water, similar to how sweating cools our skin.
As it stands, Singapore is actively working on addressing urban heat. Most of our pavements are now shaded, we have new nature parks, and more MRT stations are being built to reduce the need for cars.
