One of the least understood risks of climate change is the hugely increased frequency of damaging extreme coastal flooding events for low lying towns like Thames and Kaiaua from just 10 cm of sea level rise.
New research from NIWA says just 10 cm of sealevel rise already locked in for the next 10-20 years will “hugely” increasing sea flooding within the lifetime of an average mortgage. “It’s not 100 years from now. It’s starting to happen already” according to lead author Dr Scott Stephens from NIWA in this Stuff article.
Stephens and a team of researchers looked back on a natural phenomenon that causes New Zealand’s sea to rise (and then fall) by approximately 10cm each year – known as the annual sea-level cycle. This gives us insight into the effect climate change will have on our coasts in the coming years.
Stephens said summer warmth gently heats the ocean waters, causing them to expand by approximately 10 cm each year. The study found floods are more likely to occur here between January and August because of the annual cycle.
“It made a surprising difference to the number of extreme sea levels we saw,” Stephens said. “What we learned from that is small sea level change makes a big difference.”
The new research, published recently in the journal Natural Hazards and Earth Science Systems, examined 120 years of oceanic records to determine how factors including the annual sea-level cycle were aligned to extremely high ocean levels.
The new research found the effects of sea level rise are only decades away, so coastal communities cannot afford to wait.
By 2040, the 10 to 20cm of climate change-caused sea level rise, on top of the 10cm of the annual sea-level cycle, combined with a spring or king tide could make sunny-day flooding – inundation without a storm – of coastal homes and roads increasingly frequent.
“Sunny-day floods… are now starting to encroach into places they didn’t before. That is going to become an increasing problem,” Stephens said.
“The very biggest events need a big tide and also need a storm at the same time. It’s the things coinciding.”
Local body politicians and planners are going to have to wise up quickly to these impacts of the climate crisis.