'Sponge city' urban design needed to help New Zealand survive climate change-induced increased rainfall - experts

Experts are urging a radical overhaul of urban design to help New Zealand survive the increased rainfall brought by climate change.

A report from the Helen Clark Foundation said the "sponge city" approach involves designing spaces to absorb rain rather than let it pool, like tiny urban forests and so-called "pocket parks".

"We have a major flood event in New Zealand every eight months and it's costing us absolutely billions of dollars," said report author Kali Mercier.

"So turning them into giant sponges essentially. We've been losing green space in New Zealand so we're becoming less absorbent over time."

That's because of our impermeable tarmac roads, iron roofs, and concrete footpaths.

The report said current urban design is "falling short", that our pipes and drains are "ageing" and "not coping with current requirements, much less up to the task ahead", and that our urban areas are less green and less able to absorb large amounts of rain.

"In lots of our new developments, we're seeing stormwater management that is being done. Incorporating more ecological practices, we need to see that happening a lot more and a lot faster," said Dr Tom Logan, Canterbury University civil engineering senior lecturer.

The sponge city model requires councils to plan for and provide green spaces, to retrofit neighbourhoods to be more absorbent, like by requiring new builds to have plants on roofs, and requiring new developments to have fewer sealed roads and car parks.

Another recommendation is to consider rates rebates for homeowners who make changes to their property, like replacing lawn with trees and putting in gravel-filled drains.

The benefits extend beyond flood protection.

"There's more water and more green space and that has a cooling effect on our urban areas. Also bringing in biodiversity, and that's really important," Logan said.

The report acknowledges it'll be expensive, but doing nothing will cost more.

"It's actually in the long run going to be cheaper and our cities will be more resilient," Mercier said.

In your own backyard you can shift sheds or fences out of flood paths, or direct drain spouts into the garden instead of the stormwater system.