This map shows inundation areas in Hawke’s Bay, under a one-in-100-year annual exceedance probability and assuming 30cm of mean sea level rise. Image / Niwa

NZ - Maps reveal NZ's hot spots for extreme coastal flooding

Just-released maps have revealed which areas of the country may be hit hardest by extreme coastal flooding.

Last year, a team of researchers warned that main centres like Auckland, Wellington, Napier, Marlborough and Nelson might be facing more than half a metre of rise by mid-century – and more than a metre by 2150.

With just 30cm of rise enough to make 100-year coastal storm surge and flooding an annual occurrence, fast-sinking parts of our coastal cities could cross that threshold by 2040.

Now, maps used with a recently-published study offer a yet-closer look at how sea level rise under climate change could compound coastal flooding problems.

Again, the work found that even small amounts of sea-level rise could drive a rapid increase in cumulative flooding from increasingly frequent events across the country.

“By 2065, there could be 40cm of sea-level rise, based on the current trajectory, or sooner where the landmass is subsiding,” Niwa scientist Dr Scott Stephens said.

The maps, produced as part of the Deep South National Science Challenge, showed large swathes of our coastline were vulnerable to flooding with extreme sea levels right now.

At present mean sea levels, some 1593sq km of area was exposed under a 10-year annual recurrence interval – or where there was a 10 per cent chance of the flooding recurring in any year.

Under a 100-year annual recurrence interval – or where there was a one per cent chance of extreme coastal flooding in a given year – the area was estimated at 1774sq km.

But another 30cm of sea level rise could greatly widen the area at risk - by another 713sq km (or 31 per cent) and 645sq km (27 per cent) under each of the intervals, respectively.

While more than 90 per cent of the exposed area was rural land, the modelling found urban spots were also at risk.

Of urban inundation areas where there were more than 10,000 people living, half were located in Bay of Plenty, Hawkes’ Bay and Canterbury.

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