One in a 100-year floods are a thing of the past and more likely to occur every decade and be much worse.
The country's water and atmosphere science body is testing a new tool to predict them and the potential damage.
NIWA says not to utilise its flood forecasting capability would be a travesty, as climate models show flooding in the future may well be worse than the country has ever experienced.
Sam Dean is the Chief Scientist for Climate Atmosphere and Hazards. He talks to Kathryn Ryan about why the technology is vital as the country is set to receive more intense rainfall events as temperatures rise.