This story is part of Covering Climate Now, a global collaboration of more than 250 news outlets to strengthen coverage of the climate story.
The country's flood risk from climate change paints a grim picture for the future, with a call for better nationwide mapping of regions most at risk.
Rising sea levels and more storm systems are sending water surging everywhere, with flooding now considered part of our future.
It comes as a NIWA report reveals Canterbury's people and local economy could be hit the hardest from river flooding because it is home to many large river systems both in the city and rural landscape.
Christchurch City Council water planner Graham Harrington told 1 NEWS flood prevention had been a priority for some time.
But one East Christchurch resident, Mike Sinclair, has to rely on a stop bank to keep water away from his property because his home is in line with the high tide.
NIWA hazards researcher Ryan Paulik said we still need to know more, adding that there was a high number of buildings, and therefore people, on land at risk of floods.
NIWA's report shows 675,000 people nationwide, and 411,516 buildings worth $135 billion are exposed to flooding in extreme weather.
There are also 19,000 kilometres of road and 20 airports at risk of being swamped.
"What our report doesn't differentiate is over what timeframes those numbers of people and buildings are exposed," Mr Paulik said.
NIWA relies on public information to gauge the risk. That information shows New Zealand needs a national flood map, he said.
"What this will enable us to do is it will compare different flood hazards risks between regions and territories."
This story is part of week-long special coverage of climate change from 1 NEWS. Other stories in the series include a look at flooding, the situation in farming, and concerns over ocean temperature rises.