The coast is under threat

ReadingRoom

A climate researcher on the future of coastal housing (there is no future)

I was once interviewed for television while standing on the beach not far from my home. At one point, the interviewer said to me, “So, by the end of this century, all these houses we see along the beach here will be gone?”

It was a pretty confronting moment. Most of those houses have been there for decades. Each one is someone’s home, and those people are part of my community.

I paused and took a breath, looking up and down the beach, before replying. “Yes,” I said.

Sooner or later, homes that close to the shore will either have to be moved or they will be washed away. The reality  is that, in many places, the coastlines are on the move, and we had better move with them. Some parts of the coast are rocky and fairly impervious to wave action, and other parts are actually growing as waves and currents deposit sediment. Other stretches already feature sea walls, which can be quite a good barrier and offer short-term protection, but the trouble is that all kinds of sea walls tend to get eaten away eventually. They are, at best, a temporary solution.

When a storm affects the coast, three things happen. First, the low pressure near the centre of the storm lifts the level  of the sea surface up, typically about 20 centimetres in an average storm. The lower the air pressure and the stronger the storm, the more the sea level is raised. Second, if on-shore winds are blowing, they will pile up seawater at the coast, raising the sea level even more. Finally, wind-driven waves coming in to the beach will raise the sea level again. With just 10 or 20 centimetres of sea-level rise, the sea wall that was once just high enough to keep the waves at bay will find itself over-topped. I’ve seen just this happen near where I live in the last few years.

One of the country’s real problem areas is South Dunedin, a residential suburb inland from St Kilda beach. As well as being very close to sea level, it is built on a combination of drained swamp and reclaimed land. For now, a very sturdy and tall sea wall along the nearby beach has kept storm surge and coastal erosion at bay, but that can’t do anything to help combat the real problem: the height of the water table, or the depth at which ground water sits.

These days, the water table in South Dunedin is just below ground level, and the land is sinking slowly. The main problem with this is that, when it  rains, the rainwater has nowhere  to go. The stormwater system is largely ineffective because there is so little vertical room to move. In recent storms, fire engines were brought in to pump stormwater away because  it just couldn’t drain. That kind of problem is only going to get worse. In response, the Dunedin City Council and Otago Regional Council have established the South Dunedin Future programme, which aims to “develop and deliver a climate change adaptation strategy for South Dunedin that works, is affordable, and that the community supports.” On the table in the past have been discussions about managed retreat, and building relocatable houses to take the place of the old villas that make up the neighbourhood.

The words ‘managed retreat’ roll off the tongue easily enough, but the reality is a lot harder. Lots of the buildings that might have to be abandoned have been homes where families have grown up, or may even have lived in for generations. We are attached to our homes, whatever and wherever home is.  It is not easy to just walk away, even if we know it’s necessary. Supporting whole communities to relocate because of rising seas is a tough job, and one that as a society we have not even started working on.

At least 10,000 properties across Auckland, Wellington, Christchurch and Dunedin will completely lose their insurance by 2050

After Hurricane Katrina rumbled over New Orleans in 2005 – killing 1,800 people and inundating large parts of the city – there was talk of relocating the whole city, moving it upriver and away from the coast. As well as being prone to hurricane activity, the city sits at the mouth of the Mississippi River, on subsiding land, around half of which is below sea level. So, relocation made a lot of sense. But, despite the damage and the ongoing dangers, the city did not move. It was home to many – and most wanted to keep it that way. Today, New Orleans is still located where it was pre-Katrina, but sea levels have gone up a few more centimetres, and Atlantic hurricanes are getting more intense. In response,  the city has invested in extensive engineering works such as levees and pumping systems to reduce the risk of inundation. It has also been partly redesigned to include wetlands and floodable parks, which accommodate water and reduce flood damage. It’s  possible that all this technology in the form of pumps and levees will keep the city safe – but can it last forever? Will a time come in the next century when the city really will have to pull out for good?

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In  New  Zealand, cities like Dunedin face the same questions. Things are bound to get worse in most of our coastal cities and towns this century. Problems with stormwater drainage and coastal inundation will ramp up, and at some point a decision will have to be made to retreat – from the Kāpiti shoreline, from the Napier waterfront, from Mission Bay in Auckland, from any number of coastal settlements that have been home to many generations of people. When do we start planning to retreat? How much are we prepared to spend to stay where we are?

There are changes afoot in the policy and legislative landscape that will hopefully move us forward in our response to climate change. The Resource Management Act will be carved up into several new pieces of legislation, including something focused on climate change. In August 2022, the Ministry for the Environment/Manatū Mō Te Taiao released its first national adaptation plan, and the government has a clear agenda to help all New Zealanders deal with the consequences of climate change and best protect communities from future risks.

The responses we need to make on the ground can be very hard to deal with, and the planning timescale can be long, so the sooner we get on with thinking and talking about what we’re going to do, the better. We don’t have to wait for all the properties in a coastal community to be badly affected by coastal inundation before that community starts to fall apart. If just a few houses are damaged by storm waves, if part of the esplanade along the beach gets eaten away, if the bus stops going that way because it has become too risky, people are not going to want to live in that area any more. Here in my neighbourhood in Kāpiti, I imagine that once even a handful of houses on the front line of the dunes are badly affected, and even if a short section of the coast road suffers storm damage, a lot of home owners will head for the hills, literally.

There’s one other thing that will eventually drive people away  from  oceanfront  properties, and that’s  insurance. As New Zealand Geographic reported in September 2021, some research already indicates that many homes currently deemed ‘low risk’ – which is to say, they’re estimated to flood only once a century – will nevertheless likely start losing their insurance from 2030. In a report published in December 2020, the research team at Climate Sigma, which provides scenario analysis and asset valuation on the physical risks of climate change, predicted that at least 10,000 properties across Auckland, Wellington, Christchurch and Dunedin will completely lose their insurance by 2050.

That’s something it’s hard to reckon with around climate change. It isn’t just physical damage to coastal property, or to properties and infrastructure on flood plains, that will tip things over for most of us. Once things start to go downhill in some way, and once it starts hitting the pocket, people will vote with their feet. Neighbourhoods and even whole towns may be looking at relocation or abandonment well before the waves or the floods take over.
(Note: This article was published in error for a short time two weeks ago, before the book embargo lifted, and is republished now the book has been launched).

Taken with kind permission from the excellent new climate change book Under The Weather: A future forecast for New Zealand by James Renwick  (HarperCollins, $40), available in bookstores nationwide.