Hot in the city

Urban Heat Island Effect

You may have noticed that – like the Billy Idol song – it’s getting hot in the city.

Just in case I am showing my age and this means nothing to you here it is!

This increase in temperature is due to what is known as the Urband Heat Island Effect or UHIE.

UHIE refers to the phenomenon of built up metropolitan areas being several degrees warmer than their surroundings. This is in part due to the high levels of concrete, stone and brick, which absorb heat and then radiate it back into the atmosphere. It is also due to the increased activity of urban areas and the use of motorized vehicles and other heat emitting equipment. If you feel a concrete drive or road after a hot day you can feel the heat coming off it for a while after the sun goes down. If the wind is up then these areas cool quicker but on still days cities can stay hot a lot longer than their rural counterparts.

Not every city has experiences UHIE. This is due to design and the use of green spaces, trees creating shade and water masses that act as evaporative coolers. UHIE can also be reduced through the use of lighter coloured building materials, which reflect light and absorb less heat.

This illustration explains the effect simply.

UHIE is going to increase as the temperature does. According to the CSIRO the days are definitely going to get hotter.

Not only can this be uncomfortable but there is a safety issue. The human body doesn’t cope well in high temperatures and the more vulnerable members of our community can easily suffer from heat stress. As you will see from the diagram below we can suffer and even risk death if we over heat. Although many people have air conditioners in their work places and homes this is not necessarily the best answer. For a start they cost money to run. They may also be running on fossil fuel generated electricity, which adds to greenhouse gas emissions. They also push heat out of them and add to the heat outside of the building. Wherever possible we should try to reduce our dependence on air conditioners and try to make our spaces cooling passively. If air conditioners are the best option to keep you healthy and comfortable then we encourage households to power them with renewables, such as power you generate at home from solar, or by purchasing GreenPower through your electricity retailer.

This can be done by insulating our buildings better, to keep heat out. Read more about insulation here.

We can also keep our urban spaces cooler by planting trees for shade, using reflective roof materials, and by installing rain water tanks, downpipe diverters or raingardens to capture water.

Where possible if we can use our cars less and reduce the amount of heat generating machinery we use that will help too.

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