New Zealand has $NZ135 billion ($127 billion) of building assets at risk from river and rainfall flooding during severe weather events, according to a report described as a “first cut” at identifying the level of potential exposure.

Almost 700,000 people and 411,516 buildings are considered at risk, along with extensive road and railway infrastructure and 20 airports.

National Institute of Water and Atmospheric Research (NIWA) hazard analyst Ryan Paulik says the study, based on flood maps and data from local authorities and government organisations, highlights the urgent need for national flood maps.

“We need accurate and comprehensive information about the impact and costs of flooding today and under different climate change scenarios so everyone can plan and adapt,” he says.

Any specific event would affect only some of the exposed buildings, while potential direct and indirect economic losses are not considered by the NIWA and Deep South National Science Challenge report.

Risks for coastal areas have also been highlighted in a separate study released by the researchers that builds on previous work on rising sea levels by combining those impacts with 1-in-100-year storm tide events.

The study looks at changes in 10 centimetre increments and finds a 30 centimetre sea level rise would expose $NZ18.49 billion ($17.44 billion) of buildings to flooding, up from $NZ12.5 billion ($11.8 billion) currently, while a one metre rise would increase the exposure to $NZ39 billion ($36.78 billion)

“In the case of coastal flooding we see quite a dramatic increase in terms of the exposure elements at risk, with not a lot of sea level rise,” Mr Paulik told a seminar.

“Within that first metre of sea-level rise we are looking at doubling or tripling the current exposure of elements at risk to coastal flooding.”

NIWA says there is “near certainty” that the sea will rise 20-30 centimetres by 2040, and levels could increase by 0.5-1.1 metres by the end of the century.

“We need to put the brakes on development in coastal areas even if areas may not be impacted for a few decades,” scientist Rob Bell says.

The Insurance Council of New Zealand says improved information on potential risks is important for property buyers and councils as they look at mitigation.

“Insurers take note of any modelling that can add to or broaden their current understanding of regional flood risks,” a spokeswoman told insuranceNEWS.com.au.

“The more data like this is available, the more information property owners and prospective property owners have to inform their decision making.”