What kind of storm would it take
As infrastructure is put to the test by extreme weather events, scientists are modelling what a worst-case scenario might look like. Jonathan Killick reports.
As Auckland’s infrastructure is put to the test by extreme weather events, scientists are modelling what a worst-case scenario might look like and how the city’s buildings would stand up.
For example, take Auckland’s iconic Sky Tower. It’s rated to go ‘‘essentially undamaged’’ in winds of up to 200kph, according to SkyCity’s online fact file.
In winds of that speed, the tower would sway by a metre at the top of the concrete shaft, but would remain anchored by 2000 tonnes of reinforcing steel and foundations that go 15m beneath the earth.
That would be considered a ‘‘one-in-1000-year storm’’ according to SkyCity. It’s the highest standard that can be required in the Auckland region.
The ‘‘wind loading’’ standards are set by national building codes based on the location of a building, how tall it is and what type of material it’s made of.
The highest wind speed ever recorded by Niwa was 204kph at a weather station in Manukau Heads, while the next highest was 147kph at Auckland Airport.
During Cyclone Gabrielle, MetService recorded 152kph – also at Manukau Heads – while Auckland’s Harbour Bridge was blown by 115kph gusts.
On Friday, Finance Minister Grant Robertson told the Auckland Business Chamber that there was no point talking about ‘‘one-in-100-year events’’ any more, because the country would be dealing with them regularly.
MetService meteorologist Ashlee Parkes said cyclones were not expected to get more frequent as a result of climate change, but they were expected to get worse.
‘‘With climate change and an increase of water vapour in the atmosphere, their intensity will be greater and therefore their impacts larger.’’
She said meteorologists avoided talking about ‘‘one-in100-year storms’’, despite this being the terminology used in building regulations, because it’s ‘‘misleading’’.
‘‘Cyclone Gabrielle was a oncein-a-lifetime event given the area and intensity of impact.’’
Nick Locke, principal research engineer at consultancy WSP, said if the 152kph winds recorded at Manukau blew through the CBD, it would be ‘‘pretty gnarly’’.
‘‘It would be enough to start blowing bits off buildings and shattering glass.’’