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HEAT-SENSITIVE: Dr Ahmad Okeil is concerned about the urban heat island phenomenon.

Dr Ahmad Okeil, senior lecturer in the Institute of the Built Environment, the British University in Dubai, discusses what developers and contractors can doto reduce urban heat island phenomenon.

What is urban heat island phenomenon?

If you take two points, one in an urban area and one in a city, and measure the temperatures and compare them both, you will find the temperature in the urban area is higher most of the time.

There are several factors contributing to this. These include the materials used in the city, such as asphalt or roof tiles, which you find are a bit darker when compared to the countryside. These act as solar conductors, absorbing much of the heat.

Also in the city you have buildings with complex forms, within these forms are the gaps we call streets. If solar energy enters the gaps it keeps bouncing between the opposite façades and a portion is absorbed and reflected, until nothing is left.

Also in rural areas you have a lot of soil water and plants, which gives the opportunity for water to evaporate and cool the temperature.

Cities do not cool as fast because of the complex geometry, which traps air between buildings. Air flows over the top of the buildings, so these gaps have an air mass which keeps circulating and never mixes with the layers on top of them.

There are other factors, but these are the main ones.

What is the temperature difference between urban and rural areas?

It's location-specific and changes from day to day, depending on factors like weather and wind.

Differences as high as 10°C have been measured in rare cases; 5°C is not uncommon but the average for a whole year is about 2°C.

As it is very hot in the Middle East, a few degrees extra is going to make a lot of difference. People will feel a lot more discomfort outdoors and there will also be increased energy consumption to cool the buildings with air-conditioning.

Increased temperature also encourages the formation of smog.

How can developers reduce the problem?

To mitigate the effects you need to reverse everything we have talked about. Instead of using surfaces which are dark, use light ones.

Roofs are the easiest ones to change. The material type is not important, it is the albedo - the percentage of which a material deflects light - which is important.

For areas that have not been constructed and are still under design, you can put careful consideration to the air flow to make sure it flows between buildings.

For example, if you are building 100 towers, you should not have them all at the same height. You should make sure some are high-rise and some are low-rise, which will create turbulence allowing air to mix between the top of the buildings to the street level.

The activities we humans do, such as heating and cooling of buildings, cooking, artificial lighting and transport, also play a big part. They make the city act as a power station.

Any measures which makes the building more energy efficient helps. Developers can also determine the lifestyle of residents. So building a mixed-use development where people can walk to work will help reduce energy consumption.

Is enough being done in Dubai to prevent the problem?

It hasn't really been taken into consideration until now, but this will change very soon with the introduction of the proposed Leadership in Energy and Environmental Design (Leed) system for the UAE.

You can get Leed points for mitigating the urban heat phenomenon. One of them is roof-related measures and you get a point for painting the roof white or planting on it.

The other one is non-roof related, which gives you the opportunity to use landscape around the building or change the layout of the building.

Developers are taking notice because anyone who wants to build a Leed building will have to take the problem into consideration.

Can contractors play a role, too?

If they have awareness of the issue. If they get a design where all roofs are supposed to be covered with dark roof tiles they can raise the issue with the developer and the design team. But it is up to the design team whether they take any notice or not.

Will these measures add to the cost of development?

No. It is not going to cost any more, it is just the careful selection of colours. There have been some reports done from cities where cool-roof programmes have been conducted and the estimated savings in energy consumption has been in the range of hundreds of millions of dollars.

Are any new developments actively following your methods?

Not yet, but I expect HH Sheikh Mohammed's green building declaration will make authorities, developers, contractors and designers find ways of making this come through.

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