Concern on 'islands in the sun'
Photo: Craig Abraham
Melbourne's planned "activity centres" will become unpleasant during summer if action is not taken to reduce the city's urban heat island effect.
A Monash University study on high and low-density areas of Melbourne has shown that suburban activity centres - a key plank of the planning blueprint Melbourne 2030 - will be hotter than other areas as they gradually build up.
This is a concentration of the urban heat island effect. Cities, with their warmth-absorbing concrete and lack of vegetation, produce and hold heat more than country areas.
Depending on conditions, Melbourne is usually between two and three degrees hotter than regional areas. The central business district can be seven degrees hotter on extreme days.
During summer, the urban heat island can exacerbate heat waves and affect vulnerable people such as the elderly.
Monash University PhD student Andrew Coutts studied several types of suburbs and areas across Melbourne, from high density to the rural fringe. "As you develop these activity centres they will have unpleasant conditions for longer periods of the year. At the end of summer all around Melbourne it is dry and warm, but in the period leading up to summer and spring, the differences will be seen," he said.
The urban heat island effect would be intensified with global warming, Mr Coutts said.
To plan for this, Mr Coutts, from Monash's School of Geography and Environmental Science, suggested activity centres get more vegetation - which has a cooling effect - and that different building materials are used: less asphalt and different roof surfaces that reflect heat instead of absorbing it.
Fellow Monash student Cheryl Walker is also studying Melbourne's heat island effect. She found that the island has recently moved west. Using satellite data, Mrs Walker showed that grasslands to the north and west have dried off and instead of being a cooling agent, have acted like concrete during the city's prolonged drought.
"Generally the heat island sits over the CBD and you'll see a temperature drop about five kilometres out. But with my study, it extended further, about 25 to 35 kilometres to the west, and the island was a lot bigger than you would normally see," she said.
While the urban heat island is likely to shift back towards the south-east in winter, it is likely it will again move to the north and west in summer, Mrs Walker said.
"This will happen especially if it is dry, and might be a more common pattern in the future if we get less rainfall and temperatures increase," she said.