Go green to reduce city’s temperature

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  • Tuesday, 10 Mar 2015

WE ALL have probably heard the familiar lament among older urbanites that today’s generation has been spoiled by modern comforts and technologies.

For example, in the past, cars did not even come with air-conditioning yet people were still comfortable.

Unfortunately, the change we are feeling is all too real and it has been shown that urbanisation causes temperature in developed areas to increase dramatically.

As cities become larger in size, it actually creates its own microclimate. This is due to the materials that we use to build our cities such as concrete, bricks and glass, which have a higher degree of heat retention as opposed to the original natural vegetation from the forest.

You will probably notice that a brick wall will continue to radiate heat accumulated during the day well into the night.

Hence the complaints of many single-storey terrace house owners that they cannot sleep without some form of air-conditioning.

Imagine this heating process happening on a larger, city-wide scale. Imagine how much heat is released into the general atmosphere. I am sure all of you have experienced this situation before — after rainfall on a hot afternoon, you would expect the temperature to drop but when you actually get out of your house or car, it seems even hotter than before.

This is due to the tarmac or asphalt on the roads releasing heat via the rainwater, as most of the water is evaporated. The release of heat as well as the increase in humidity will actually make it hotter.

The retained heat is not the only problem with regard to the urban heat island effect. The reflectance of heat towards the atmosphere is another. Generally, all surfaces reflect heat differently and this is known as the albedo.

Albedo, simply put, is the measure of the reflectivity of the earth’s surface. When we build a city, we change the general albedo of an area and the use of glass, especially, increases the reflectance of surfaces.

In the extreme, when coupled with unfortunate design, it can be as serious as the case of the car being melted by the concave surface of the “Walkie-Talkie” shaped building in Eastcheap, London. The car owner had parked his car in the street, and when he returned about two hours later, he found that parts of his car, including the wing mirror and badge, had melted.

Of course, this is in an extreme case as we would normally feel the reflecting heat as a distinct discomfort, rather than something more serious.

According to studies done by several universities, the range of temperature differences between a tropical city like Kuala Lumpur and the forested areas of the same region can be as much as 4 to 6°C.

This is a huge difference and the impact is not just general discomfort but also the immense increase in energy needed to cool many of the buildings and vehicles in these urban areas.

We are losing millions of ringgit in energy costs and with the price of energy increasing, the cost will only get higher.

This is why government efforts and green rating tools such as the Green Building Index (GBI) all promote certain measures to reduce the urban heat island effect.

Among the most frequently mentioned measures are:

• Increasing tree and vegetative cover whenever possible. There should be more softscape rather than hardscape in the landscape of a development. Even hardscaped areas can be softened by using products such as grassed pavers, or by using low heat retention materials;

• Creating green roofs (also called “rooftop gardens” or “eco-roofs”). Green roofs are not only good for preventing the green island effect but actually helps insulate the building;

• Using cool/low thermal retention materials for everything. This applies to paving, streetscape roofs and other such elements which are exposed to solar radiation; and

• Using lighter colours whenever available. This again applies to all elements of the urbanscape from buildings to landscaping. Roofs and walls should be painted in lighter colours. This even applies to roads. By using pavements with light-coloured concrete mix or replacing asphalt with light-coloured alternatives, our cities may be able to lower average temperatures.

Of course, the best form of mitigation is prevention and planning. When we plan new communities, we need to look into planning for reduction of the heat island effect.

Tools such as the GBI township tool help to ascertain areas of emphasis that need to be looked at.

Communities and new townships need to be planned right from the start to fight the urban heat island effect as to do it in hindsight is far more costly and requires a far greater effort.

Community planning should be interspersed with areas of parks and bodies of water to ensure the local microclimate is suitably balanced.

Good city planning and heat island mitigation efforts have multiple interrelated benefits, including cleaner air, improved human health and comfort, reduced energy costs, and lower greenhouse gas emissions.

A disturbing trend nowadays is the conversion of urban parks and greenery into new developments due to the value of the land they sit on.

Local authorities need to take this consideration more seriously and prevent green areas already allocated for parks and open areas from being developed.

Local communities should rally together and create a groundswell of education and a change of mindset with regard to the environment.

Let us together try to stop the mass culling of trees in our urban greenery and conversion of previously pockets of green space in the name of progress and urban renewal.

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