Few businesses in New Zealand's biggest city are fully prepared to deal with the impact of natural disasters, new research suggests.

Findings of a study released this morning also revealed just a small number of Auckland businesses improved emergency plans after a big storm hit the city in April.

That event brought heavy rain, flooding and cyclone-strength winds of up to 140km/h, knocking out power to thousands of homes and stopping flights in and out of the city.

Researchers working under a national science collaboration surveyed small to medium-sized businesses in Mt Albert, New Lynn, Glen Innes, Devonport, Titirangi and Glendowie to find out how the storm affected their operations.

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Of 71 businesses surveyed, three quarters or more were unable to function without key infrastructure services.

Three quarters reported not being able to function without telecommunication, 84 per cent couldn't operate without a water supply and 96 per cent without electricity.

Lead researcher Dr Alice Chang-Richards, of the Resilience to Nature's Challenges project, said the findings highlighted a "large gap" in emergency preparedness in the businesses, which were reliant on services because they didn't have back-up generators or water tanks.

The study also found that 20 per cent of businesses didn't have an emergency or business continuity plan in place.

Of those that did, many noted that they didn't practice it.

"Natural disaster events are stressful, and we often don't think clearly during them," Chang-Richards said.

"This is why practice and preparation are key, as they allow us to have a muscle-memory response to the event, rather than having to remember and comprehend the plan before being able to act on it."

Further, just a small number of the surveyed Auckland businesses reviewed and improved their business model after the storm.

"The 96 per cent of businesses who did not review and improve their business model could not foresee a way to cope with disruptions caused by natural events in the long-run, as they failed to revise their business model to adapt to unexpected changes."

Auckland Emergency Management acting director Sarah Sinclair said all businesses were encouraged to plan how they'd operate without the essentials.

"Some emergencies are short-lived, but some can last days to weeks," she said.

"Having access to supplies and having plans in place for businesses and households to talk about and practice is vital."

Auckland is vulnerable to a range of natural threats and climate change would make extreme storms like this year's a much more frequent occurence.

Under a mid-range scenario of 30cm of sea level rise over the next 50 years, a once-in-a-century flood event like the January 2011 storm that put much of the Northwestern Motorway underwater would happen once every four years, while 40cm would make it a two-year occurrence.

A 70cm rise would make it a monthly event.

A major volcanic eruption in the city could also force the evacuation of tens of thousands of people, and have an economic impact of up to $10 billion in the first year alone if one struck in Auckland's industrial heartland.