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Global Bioweather

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The Urban Heat Island Effect

You sit on your shaded veranda and enjoy a cool drink. The sea breeze blows gently through the large open windows and coconut trees provide shade from the sun. Dream on: you are more likely one of the million city dwellers living in a brick or concrete bunker, built to save energy during frosty winter months. An environmentalist at heart, you installed small and double-glazed windows and insulated walls and ceiling. Good on you. To beat the summer heat, you rely on air conditioning – if you can afford it and if you have the electricity to run it. Open the windows? No way, burglars are in the streets. Anyway, the air outside is either hotter than inside or laden with pollutants.

Studies showed that the majority of heat wave fatalities occur in inner-city areas. The asphalt, brick and concrete jungle absorbs heat and retains it well into the night. On average, the inner city is 5 to 8°C hotter than the surrounding countryside – the heat island effect that NASA researched in 1998. Sensors in aircraft and satellites demonstrated that artificial surfaces reach temperatures 20°C-40°C higher than natural surfaces do – Salt Lake City rooftops, for instance, were 71°C. These figures also provide the answer: cities need more natural surfaces, especially trees, to cool down.

Unventilated apartment buildings and rooms without air conditioning can reach temperatures in excess of 50°C during heat wave conditions. Even if ventilation is possible, the temperature drops to just above the outside air temperature. Since hot air rises, the top levels of apartment buildings suffer most. Insulation will keep the heat out for a day or two. But eventually the room succumbs to the environment and the insulation becomes a curse.

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