Under a Green Umbrella

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Monday, November 17th, 2014
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It’s no secret that the searingly hot summers of recent years have affected the function, liveability and health of our cities.

Irrespective of the impacts of climate change, it is anticipated that our cities will get hotter by around one degree Celsius per decade.

Why? Because our cities often seem like concrete jungles that trap summer heat and create oven-like conditions that are up to five degrees Celsius hotter than the surrounding rural areas. Melbourne City Council, for instance, has found temperature variations of up to four degrees between the city centre and outer suburbs.

We’ve created this phenomenon, known as the ‘urban heat island effect’, with our dark coloured roofs, walls, roads and even cars, and with our diminishing number of shading trees and heat-absorbing greenery.

There are steps we can take to cool our cities. The City of Sydney is trialling a lighter-coloured pavement, while BlueScope Steel’s cool roofs reflect sunlight back rather than trapping it and increasing average temperatures. However, the most obvious is to increase the number of plants and trees in our urban communities. Trees combat the urban heat island effect because they reduce air and surface temperatures – sometimes by as much as 25 degrees Celsius.

The 202020 Vision, a collaborative plan to increase the amount of green space in our urban areas by 20 per cent by 2020, has analysed the urban tree canopy across Australia, finding Hobart has the densest tree cover of our capital cities, at 59 per cent. Adelaide, on the other hand, has the lowest proportion of tree canopy, with just 27 per cent.

Researchers at CSIRO recently assessed the impact of different kinds of green areas on temperatures in residential buildings in Melbourne’s business district, finding that doubling the coverage of current vegetation would create ‘green umbrellas’ that reduce summer temperatures by half a degree. While that doesn’t sound like much, half a degree would be enough to reduce mortality in the over 75s by around 30 per cent.

The new Green Star – Design & As Built rating tool rewards projects when at least 75 per cent of the total project site area comprises building or landscaping elements that reduce the impact of the heat island effect. This includes vegetation, green roofs, roofing materials such as shading structures, water bodies and green walls.

Parks and green spaces have long been associated with better physical and mental health, reducing stress and obesity-related illness by encouraging physical activity. Measures that tackle heat island effect in our cities can connect us into a ‘virtuous circle’ that creates more livable, healthy and sustainable cities.

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