'Massive impacts': $180 billion of homes on flood-prone land – report

A major new report is warning that more than a thousand seaside homes could suffer significant damage from extreme weather by 2060.

And hundreds of thousands of homes worth an estimated $180 billion are in flood-prone areas, according to Our Marine Environment 2025 from the Ministry for the Environment and Stats NZ.

The fourth and latest stocktake draws together peer-reviewed research, government reports, mātauranga Māori and official statistics.

The report said climate change and human activity is putting increasing pressure on the oceans and coasts, affecting communities, industries and ecosystems.

Among its findings are that New Zealand's oceans are warming faster than the global average; marine heatwaves are becoming more frequent and intense; the risk of invasive species and marine disease is increasing with climate change; and wetlands, dunes and native vegetation are being degraded.

Environment Ministry chief science adviser Alison Collins told RNZ New Zealand's oceans were warming at a rate of 34% faster than the global average likely because of the country's position as a small island in the middle of the South Pacific.

"It is likely that it's to do with changes in ocean circulation and also wind patterns, and we're seeing something similar around the coast of Australia as well."

In terms of species impacts, 91% of New Zealand's seabirds and 35% of its marine mammals were threatened or at risk, she said.

Warming seas almost opened the door to invasive species with climate change creating conditions for pests, she said.

The report found that in 2023, about 219,000 homes worth $180b were in coastal inundation and inland flood zones.

An estimated 1300 homes – worth $900 million at current property prices – are set to experience greater than 20% damage in one or more extreme events between 2026 and 2060.

It gives the example of major erosion for Southland's Bluecliff residents, where between 5m and 30m of erosion occurred along the shore of the Waiau River estuarine lagoon after a storm on September 21, 2023.

It points out that thousands of kilometres of roads, water pipes, and buildings worth a combined value of $26.18b were assessed in 2019 as being vulnerable if sea levels rise by 0.6m.

Under current climate conditions, about 288 landfills may be exposed to coastal flooding, and this increases to 379 with a sea-level rise of 0.4m, the report said.

It found that over the next 20 years, New Zealanders are expected to build up to 76% more seawalls and similar coastal protection structures, to try and stop erosion and sea level rise.

"We can build some resilience for our coastal communities with seawalls, levees and other engineering options. But these options can have an environmental cost as coastal habitats and ecosystems are trapped between rising seas and built structures," the report said.

Collins said some of the most exposed areas were in Wellington and Dunedin because land subsidence, high water tables – particularly in Dunedin – and sea level rise.

Sea level rise was variable across the country, she said.

"Some parts of New Zealand are obviously rising due to land uplift which slows down sea level rise, but in other places we are seeing sinking which makes it much worse. Even without land movement sea levels are expected to rise by at least 20 to 30cm by 2050, compared to 2005 levels.

"Once sea levels reached that height, a coastal storm that used to happen perhaps only every 100 years could start happening every year."

The report found that warming seas and ocean acidification are affecting the fisheries and aquaculture industries, which contribute $1.1b to the GDP, and support more than 14,000 jobs.

New Zealand's oceans are warming 34% faster than the global average warming rate, due to changes in atmospheric circulation and ocean currents.

Marine heatwaves – which the report finds will become more frequent, intense and long-lasting with climate change – have caused substantial decreases in fish catch and large losses in farmed salmon and mussels.

The report said warmer seas change the migration of fish populations and may reduce the growth rate of flat oysters and blue cod.

While warmer seas might increase certain types of fish, such as snapper and trevally, it is also likely to increase fish and shellfish diseases – such as 'milky white flesh syndrome' in snapper.

Increasing sea-surface temperatures, and ocean acidification are likely to increase toxic algal blooms, which accumulate in shellfish and fish and can also make people seriously ill.

Collins said in the west of the North Island spent 88% of 2022 in marine heatwave conditions which was putting stress on the marine environment.

A circulation shift, or subtropical front, had moved 120km west, she said.

"And that has massive impacts, that's like a conveyor belt moving delivery of food and affecting our food webs and our ecosystems quite significantly."

The report also outlined how significant cultural and archaeological sites are vulnerable to climate change, which could affect New Zealand's cultural identity, connection to the environment and tourism industry.

It said marae and urupā (burial sites) were at risk of damage from extreme weather and that throughout the country – 191 marae are within 1km of the coast. That put cultural identity – through the passing on of knowledge and tikanga – at risk.

Nearly 2000 archaeological sites along the coastal zone are highly vulnerable to erosion from sea-level rise, and 1564 are at risk of flooding from the sea.

Over 120 public conservation sites and parts of 21 walking tracks are vulnerable to erosion, the report found. That includes four Great Walks – the Abel Tasman, Heaphy, Queen Charlotte and Rakiura tracks.

Some experiences for New Zealanders and international visitors could be lost altogether without action on climate change, the report said.

Collins said the research was about making the evidence clear, so people understood what was happening.

"Not just for government, and yes of course it will be feeding into our adaptation work thinking about what we need to be considering as part of the reform of the Resource Management Act, but it's also to inform communities, iwi, individuals so that we can all work together.

"And I know that climate change can feel huge and distant, but this report I suppose is really trying to make sure that we understand what's at risk – you know, things like the Hauraki Gulf, Kaipara, Fiordland – they're all really important things for us."

A companion report that was released alongside the technical report uses case studies to give some examples of what was possible, she said.

"For example, Kaipara Moana is reducing sediment and planting native species, Fiordland Marine Guardians are protecting biodiversity."

The report aimed to make something that seemed huge "actionable" by "connecting those global drivers to very local choices", she said.

By Ellen O'Dwyer of rnz.co.nz