Climate change: How sea-level rise will work invisibly - paralysing towns and cities from underground

When we think of sea-level rise, we see waves slamming into coastal areas and flooding houses.

But it will also work in an invisible way, paralysing towns and cities from underground. 

And Petone on Wellington’s harbour has just 20 years to figure out a way to stop it. 

Scientists initially thought Petone had 50 years to deal with sea-level rise but new research shows the land there is sinking - and that drastically speeds up how quickly the water will rise.  

"It's incredibly vulnerable to changes in sea level," climate scientist Richard Levy told Newshub.

"We only have 20 years, maybe less." 

It'll impact a huge number of people and businesses - not just those at the water's edge. That's because just 30cm of sea-level rise is enough to incapacitate the town’s stormwater system.

"The drainage system is designed for today but as sea level rises that drainage system stops functioning as it’s been designed to function," Levy said. "You get ponding behind the dunes, you get ponding in the streets, you get flooding that is perhaps something that most people aren't thinking about at the moment because it's out of sight, out of mind."  

Under all the concrete and asphalt is a complex gravity-based drainage system that will need to be rethought and redesigned. But are people worried? 

"Well clearly it's a worry, I am aware of the problems that we've got with climate change and rising sea levels so it's on my mind," one Petone resident told Newshub. 

"Twenty-30 years doesn't worry me so much but five-10 might, we'd hope that the Government and the council might have a plan to save us by then," another said. 

"I'm not worried, I've been in Wellington my whole life and I haven't seen these sea levels rising in all that time," said another.

Whether people believe it's happening or not, the Wellington Regional Council is planning for it - and the cost to fix the underground stormwater pipes which keep Petone running will be eyewatering.

"When it comes to infrastructure buried in the ground like that we're talking tens to hundreds of millions of dollars," said Iain Dawe, a climate change and natural hazards specialist at the Wellington Regional Council. "In all places like this where you have limited budgets, you have to start doing the cost/benefit calculations."

Work has accelerated for a network of pipes that can cope with the rising sea and identify which areas will be hotspots - or wet spots - for flooding. "But it may well be the case that we simply cannot afford to protect everywhere," Dr Dawe said.

Eventually, some people will have to leave their homes and find drier, safer places to live. 

You might be thinking, 'Well I don’t live in Petone or near the coast - so I'm fine.' But scientists say we don't get off the hook that easily. 

Even if the waves aren't lapping at your feet, they might be eroding a key piece of infrastructure near you. Eastbourne just around the Petone waterfront, for example, is relatively unscathed by sea-level rise - but the only road in and out is in big trouble. 

"You may think you're living in an area that's resilient or protected from climate change that's not going to be directly affected by sea-level… but it might be that the road that you have to use to get to your house is highly exposed to the point where you can't actually get to the shops, your home to the hospital, your home to your place of work," Levy said.

Climate change: How sea-level rise will work invisibly - paralysing towns and cities from underground
Photo credit: Newshub.

Levy and Tim Naish's new Sea Level Rise study, which Newshub first reported on Sunday, is telling us the cities we imagined for the future need to become the cities of today; re-built to absorb water, not repel it. 

"Internationally we talk about sponge cities," climate change researcher Judy Lawrence said. "These have been talked about for decades but they're now actually being built in China, in Japan, Europe. 

"The idea of a sponge city… is it takes up water. So in a city where you can plant trees and have vertical gardens on buildings, have low-lying areas like some of the big parks… opened up for vegetation… so the ground becomes the sponge."

It's an idea that could help Petone and the country's other low-lying areas adapt to sea-level rise.

However, the only way to prevent it at a catastrophic level is to stop pumping Co2 into the atmosphere.