In some parts of the country, such as areas in Auckland and Wellington, the data shows the sea level is rising twice as fast as previously thought.
This is due to the land sinking at an alarming rate.
Naish said the greatest effect sea level rise would have on Whanganui would most likely be the rates of erosion around the Whanganui river mouth, around Castlecliff and Kai Iwi cliffs, among other areas further north.
"The cliffs are already eroding because the land is rising there, and they get attacked by the westerly waves and when big storms come in," Naish said.
"With the sea level rising that just increases the rates of erosion so, yes, you'll see more cliff retreat."
South of Whanganui to around Turakina and Whangaehu it was more of an open beach without cliffs, and Naish said around that area the rivers would just back up more and the estuary would get bigger.
Whanganui Mayor Hamish McDouall said there had been highly noticeable erosion around Kai Iwi over the last 50 to 60 years.
"There's engineering you can do to prevent that erosion, but equally you don't want to mess with the natural processes," McDouall said.
"Falling cliffs will be a constant danger over the next few decades, I would imagine, and requires quite considerable attention."
Naish said Whanganui's land itself was fairly stable and would not be hugely affected by the land sinking, subsiding at an average of a millimetre per year.
"You're going to see the global average sea level rise, which is 30 centimetres by 2060, 50 to 60 centimetres by the end of the century."
"But Whanganui itself is unlikely to see more than that.
"As you go south of Whanganui the land is sinking a little bit more, but really that whole length of coastline is at the moment relatively stable."
Naish's career has had him working closely with Whanganui, as the region has one of the world's best geological archives of past global sea level changes and records of temperature - these archives are found in the land itself.
He said this was due to a unique set of geological circumstances Whanganui had, which included the land sinking, the specific water depth and a lot of sediment build-up from the erosion of the hills and the surrounding mountains.
Although the sea levels rising held importance for the Whanganui District Council, McDouall said the principal climate change threat for the Whanganui region remained increased rainfall and increased river flooding.
Naish said the Government required councils to take into account climate change and sea level rising when they made any decisions about zoning, planning and new developments.
"I'm just the scientist, and our group provides the latest information councils need," he said.
"So what I say to councils is: here's some new information that's really, really helpful, and it will help with your planning and decision-making.
"The Government is going to require you to make sensible decisions and not allow things to be built in really risky places."
McDouall said as soon as there was new evidence available, responsiveness must be increased.
"So I think the key thing is to be using this to inform plans and strategies going forward. To me that's vital.
"We'll assess the details and to see if there's any particular responses we can have to it."
Part of the plan to tackle flooding was already put in place before McDouall became mayor, putting clear prohibitions on building in flood-prone areas.
"People desperately want to build on some flood-prone areas because most of the time it's absolutely beautiful and just across the river.
"But the reality is that sea level rise will impact the lower reaches of the river."
Naish said his understanding was the Whanganui stopbanks were "pretty good" but if a sea level rise caused a rise in the river as well, the stopbanks could be a concern.
McDouall said all of New Zealand had to take into account future sea level rises.
"Whether it's happening 50 years earlier or later, it's an inevitability," he said.
"This is a nationwide thing, there really needs to be a nationwide response. It happens better when we're doing it all together."
The data is available to online at https://www.searise.nz/maps
