Scientists are taking a sharper look at how New Zealand's coastlines are changing, in a major new project to help prepare the country for a wilder future.
The just-launched programme will also reveal the myriad risks facing those seaside communities already sitting in what Niwa's Rob Bell called a "flood sandwich".
"New Zealand's coastal communities are already exposed to occasional coastal erosion and flooding, typically associated with storm surge and waves coinciding with high spring tides," he said.
"With ongoing sea level rise, there will undoubtedly be more intense and frequent coastal erosion and flooding events, compounded by rising groundwater levels and more intense rainfall."
These ongoing changes would "fundamentally re-shape" our coastlines and continually re-define New Zealand's future coastal hazards, he said.
About 72,000 New Zealanders are already exposed to extreme coastal flooding, along with about 50,000 buildings worth $12.5b.
This risk increased markedly with sea level rise, particularly during the first metre of rise we could expect this century.
There was near certainty the sea would rise 20cm to 30cm by 2040 and, by the end of the century, depending on whether global greenhouse gas emissions were reduced, it could rise by between 50cm and 1.1m.
That put an extra 116,000 people at risk.
On top of that, some 700,000 people and 411,516 buildings worth $135b would be exposed to river flooding that could come amid extreme weather.
In our largest city, more than 43,000 Aucklanders are directly threatened by rising seas - up from 34,700 people in 2001.
In the eventual firing line of rising water will be Auckland Airport, Middlemore Hospital, much of the CBD area - and even the local Civil Defence offices.
Local Government New Zealand has urged ministers to launch a new state adaptation fund and risk agency, so they won't face the threat without the resources and expertise they desperately need.
Its own research shows as much as $14b of ratepayer-owned infrastructure is at risk of sea level rise - including about $2.7b of roading, water, and building infrastructure threatened by as little as half a metre of it.
Again, the cost ramps up sharply at each increment of sea level rise, with the data showing that $5.1b worth is at risk at 1m of sea level rise, $7.1b at risk at 1.5m and $14.1b at risk at 3m.
In one part of the programme, led by Associate Professor Mark Dickson and Dr Murray Ford of the University of Auckland, researchers would carry out the country's first ever erosion vulnerability assessment.
That involved compiling historic aerial pictures of New Zealand's shoreline - spanning right back to the 1940s - and developing new ways to use satellite imagery that have become widely available over the past decade.
"Importantly, the database will also enable us to tackle the difficult science problem of what is actually driving coastal change," Dickson said.
"We know that sea level rise is likely to increase coastal erosion rates, but many other factors are also important controls on coastal erosion, including natural variability in sediment supply to beaches, vegetation changes, and various human impacts.
"Working out the role of these different controls at different locations around the country will have a major bearing on efforts to model future erosion rates under sea level rise."
Another element, led by Professor Karin Bryan at the University of Waikato and Niwa's Dr Scott Stephens, aimed to find new methods to work out the flood hazards that rivers and estuaries posed to people.
"Many of New Zealand cities and rural communities are developed around estuaries and harbours, which are vulnerable to a 'flood sandwich' between rainfall delivered by rivers in flood and high sea levels driven by high spring tide, storm surge, waves riding on the back of a rising mean sea level," Bell said.
Using the Waihou/Piako River Estuary in the Hauraki Plains as a case study, the researchers would investigate how shifts in the shapes of estuaries, or adding seawalls and stopbanks, could change flood risk.
A third part of the programme, meanwhile, would develop planning processes that were designed to be more adaptive than reactive.
Currently, councils were limited not just by fragmented data about changes in shorelines, but adaptation practices that focused merely on recovery or "holding the line" against what was irreversible sea-level rise, Bell said.
"Decision makers in New Zealand need new nationally-consistent data and adaptive tools and planning approaches to manage and enable adaptation for changing, but uncertain coastal futures," he said.
"Much of that uncertainty for coasts relates to how quickly global emissions can be reduced to keep global temperatures below 2C before runaway polar ice sheet instabilities become entrenched."
The new programme was being supported through Resilience to Nature's Challenges, one of 11 collaborative science efforts funded by the Government.