New maps released showing where coastal flooding could occur

Thu, May 25
Coastal erosion near Whitianga's Mercury Bay Boating Club.

New maps showing areas where extreme coastal flooding could occur aim to fill gaps for places that do not have this data available.

The maps were created by NIWA and the Deep South National Science Challenge.

They show a large storm tide along with the sea-level rise the country was expected to experience with climate change.

NIWA chief coastal scientist Dr Scott Stephens said the maps would help shape decisions on how to adapt to sea-level rise.

"Coastal flooding is a global hazard that impacts New Zealand, with rising sea levels already causing more frequent and intense flooding along many coasts.

"We have created maps that help identify the changing risk to land, property, and infrastructure from rising seas at a regional and national scale."

It was hoped the information would help councils and governments to know where to conduct detailed investigations when developing adaptation strategies to protect our coastal communities.

Coastal flooding was particularly likely when high tides, storm surges and large waves occurred simultaneously, Stephens said.

At these times, low-lying areas could be inundated when high seas overtopped or even broke barriers and caused rivers to back up inland.

This could be life-threatening, as well as destroying property and infrastructure and having severe impacts on the natural environment and ecosystems.

"With much of our major infrastructure and roughly 65% of New Zealanders living within 5km of the coast, this is an issue that will impact many of us, so we must be aware of what's coming and be prepared to adapt," Stephens said.

The maps were used in new research that examined New Zealand's increasing exposure to coastal flooding with sea-level rise.

It found small amounts of sea-level rise would drive a rapid increase in cumulative flooding from increasingly frequent coastal-flood events nationally, and 30% more land area would be regularly flooded after 0.3m relative sea-level rise.

"By 2065, there could be 0.4m of sea-level rise based on the current trajectory, or sooner where the landmass is subsiding."

Stephens said the maps were not designed for assessing exposure to individual properties as many councils already had detailed maps for that purpose.

"The advantage is that they fill in gaps for areas of the country that don't currently have this data available, they provide nationwide information, and they include many scenarios of sea-level rise."

The maps were also intended to help the financial industry, infrastructure, and service providers assess risk.