Recent landslips have shown some New Zealand cities have problems dealing with stormwater. Now green roofs, which have proved popular in Europe, are being trailed at Auckland University and could change the way we use our rooftops.
They involve planted rooftops, and are intended to catch enough rain to stop stormwater runoff.
"The rainfall falling on the system is soaked up and then evaporates, or is used by the plants, so in essence, for these small storm events, no runoff should be generated from the rooftop," Dr Elizabeth Fassman of Auckland University says.
Most of the built up surfaces in urban areas are roading related, but comprise of about 40% roofing, which could all be potentially covered in Fassman's small plants. They can handle sun, rain and wind and do not need much attention. The idea is that after the initial planting, you can just leave them to it.
"It is quite a simple system, you can put it on pitched roofs, you can put it on flat roofs, the design's a bit different, but it certainly can be done," she says.
The effects of stormwater runoff are all too obvious, and toxic chemicals from roofing materials are among the pollutants. Auckland, like other cities, is struggling to cope.
"That's quite a major problem for the Auckland region, particularly with the extra development that's happening," Paul Walbran of Auckland Regional Council says.
Green roofs are also thought to reduce smog, lower temperatures in summer, protect the buildings they are on and even insulate them.
"Over the long term you'll see significantly reduced energy costs and energy consumption," Fassman says.
