Raising flood-threatened houses by a few metres could prove a cheaper option than re-building for homeowners wanting to stay put for longer, Photo / NZME
Raising flood-threatened houses by a few metres could prove a cheaper option than rebuilding for homeowners wanting to stay put for longer, new research finds.
Yet that wouldn’t solve all the problems expected to mount in our coastal communities as climate-driven impacts hit home.
In the study, coming just as the Government has made it possible for people to search 25 years of disaster-related claims, Niwa commissioned construction cost experts WT Partnership to provide cost estimates for different types of building.
They found that, for buildings of timber and pile construction, lifting them by 2m would be more cost effective than constructing new builds – but this still wouldn’t be financially viable for those of built from concrete.
The study’s leader, Niwa coastal and estuarine physical processes scientist Dr Christo Rautenbach, said raising homes could offer another option for those who lived in coastal lowlands.
“We know that the impacts of flooding have been felt by many, and the risk isn’t going away,” he said.
“Communities must adapt, but certain solutions like relocation inland can be unpopular and seen as a last resort, so it’s important to assess alternative coastal adaptation options.”
The potential scale of New Zealand’s vulnerability to climate-related impacts is vast.
Considering one estimate of the current rateable value of exposed residential property on our coasts, $17 billion worth of homes could be at risk.
Add together all private and public properties and assets lying in coastal floodplain areas - and that sum climbed to nearly $150b.
According to New Zealand’s latest risk assessment, 72,065 people live in areas exposed to that once-a-century risk, while about 675,500 people live in areas prone to flooding.
But those figures were almost certainly under-estimates, given more recently released modelling found main centres like Auckland, Wellington, Napier, Marlborough and Nelson might be facing more than half a metre of rise by mid-century – and more than a metre by 2150.
With just 30cm of rise enough to make 100-year coastal storm surge and flooding an annual occurrence, fast-sinking parts of our coastal cities could cross that threshold by 2040.
This year, another Niwa-led analysis indicated that, at present mean sea levels, some 1593sq km of area was exposed under a 10-year annual recurrence interval – or where there was a 10 per cent chance of the flooding recurring in any year.
Under a 100-year annual recurrence interval – or where there was a one per cent chance of extreme coastal flooding in a given year – the area was estimated at 1774sq km.
But another 30cm of sea level rise could greatly widen the area at risk - by another 713sq km (or 31 per cent) and 645sq km (27 per cent) under each of the intervals, respectively.
While more than 90 per cent of the exposed area was rural land, the modelling found urban spots were also at risk.
Of urban inundation areas where there were more than 10,000 people living, half were located in Bay of Plenty, Hawke’s Bay and Canterbury.
Rautenbach said his team’s latest findings indicated that some property owners may be able to stay put for longer, “even taking into account future exacerbation from climate change, albeit with extensive modifications”.
But he also cautioned that these preparations were complicated.
There were a limited number of specialised houses lifting contractors in the country and, although raised homes remained dry, surrounding land and services will still be affected.
“The study also did not include hidden expenses, such as temporary accommodation, storage costs, and the development of supporting community infrastructure such as roads, water and wastewater services.
“With storms intensifying, rainfall increasing and sea levels rising, we must get creative with how we adapt our coastal communities.
“Transformation requires developing the right tools and it will be a multifaceted approach, and this study contributes one more piece to this complex adaptation puzzle, spanning over the social, economic, environmental and cultural landscapes.”
Another obvious question hanging over flood-threatened homes was their insurability.
Researchers have also warned that homeowners living in seaside areas at risk of one-in-100-year flood events today could lose insurance within their lifetimes – and perhaps within the next 10 years.
Over the longer term, insurance retreat from some locations was seen as inevitable, and some insurers were already looking at pricing for coastal erosion risk, on top of general flooding risk.
Toka Tū Ake EQC has just posted its Natural Hazard portal. It already provides information about past insurance claims, and more is planned to come. It could turn out to be a game changer in hazard and disaster risk education! https://t.co/nn22qh58lL
— Economics of Disasters NZ (@DisasterNz) August 29, 2023
This week, Toka Tū Ake EQC launched a new portal making it easier for people find information on natural hazard risks in their communities.
That included being able to search settled EQCover claims on residential properties and land, going right back to 1997.
“Sharing information we have about natural hazards is in the public interest,” the agency’s chief resilience and research officer Dr Jo Horrocks said.
“Seeing this information can also encourage people to ask good questions about whether any damage has been properly repaired, and what they can do to manage their own risks.”
Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.