In other parts of the world, 100-year floods had a median increase to a one-in-eight-year event over this period.
Researchers analysed tide gauge records between 1900 and 2005 and used climate simulations to identify the influence of human activity on flooding because of sea level rise at 130 sites worldwide.
For nearly half the sites, floods of the size that had a 1% chance of occurring at them in 1900 became at least 10 times more likely to happen in a year by 2005, mostly because of human activity.
However, in some locations such as Wellington, the increase in flood likelihood was many times higher.
The authors argue this is direct evidence that human-driven climate change has increased coastal flood risk, and it is crucial flood-protection planning used up-to-date flood frequency estimates.
Victoria University climate science professor James Renwick said the report showed global sea level rise because of human-induced climate change was causing changes in relative and extreme sea levels locally.
“Sea levels are not rising uniformly around the world, and local sea level changes depend on local vertical land movement and other factors. Yet, the climate change signal is now detectable worldwide and is responsible for the majority of daily extreme water level exceedances this century,” he said.
“At many locations studied, the one-in-100-year extreme sea level event is now occurring at least once per decade. Sea levels are continuing to rise so coastal inundation events will be happening even more frequently over time from here.”
Renwick said it also underlined the need for “urgent adaptation”.
“This week’s extreme wave event on the Wellington south coast reinforces the idea that we need to act now and develop response plans urgently. I trust our policymakers and politicians are listening.”
University of Waikato environmental planning research associate Dr Rob Bell said there were two factors around Wellington’s coastal storm-tide level risk.
“Wellington’s tide range is quite small and the range of New Zealand’s extreme storm-tide levels is also relatively small on a global scale, as we don’t have hurricanes or tropical cyclones. Consequently, with these small contributors to coastal flooding, even a small amount of sea-level rise (and/or land subsidence) can make rapid changes in the frequency of these events.”
– RNZ