7000 buildings at risk for every 10cm sea level rise

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A new report puts the risks of sea level rise in stark terms: numbers of people, roads, buildings, electric wires and water pipes exposed after every 10cm. Hundreds of thousands of New Zealanders may already be living in areas that could be at risk of flooding — and they’re not necessarily on the coastline.
Every 10cm of sea level rise puts several thousand more New Zealanders in a position they might rather avoid: living in an area that could be flooded by an extreme storm.
Modelling has found that each added 10cm puts at risk another 7,000 New Zealand buildings, worth an estimated $2.48b to replace, 133km of roads and 10km of railway line.
To put this in context, seas have already risen almost 20cm globally since pre-industrial times and 1m of sea level rise is considered a middling projection for 2100.
NIWA’s Ryan Paulik and Rob Bell have finished a two-year project for the Deep South National Science Challenge, where they added varying amounts of sea level rise to today’s worst-case scenarios for coastal flooding and laid that over maps of people, buildings, roads, electrical wire, airports and water pipes to see what would potentially be exposed.
The coastal floods they modelled were the worst-case scenario, like the one that hit the coast of the Firth of Thames in 2018, the kind that happens when a storm surge coincides with a big tide, waves and other factors to cause extreme damage.
Any particular area of New Zealand might expect to see a flood that big only once a century, but planners and governments are required to prepare for them: the researchers noted the New Zealand Coastal Policy Statement requires councils to plan ahead for coastal hazards for the next 100 years.
It is not only roads and buildings that might be more exposed to extreme storms as the sea creeps inland.
After 0.8m of sea level rise – a reasonably likely outcome by the end of the century — almost 150,000 people living near New Zealand’s coasts could find themselves living in areas that could be inundated by an extreme storm flood. That’s double the number of people in the risk zone from the same-sized flood today, Bell and Paulik’s modelling shows.
The researchers added increments of 10cm at a time of sea level rise to today’s worst-case flooding until they reached 3m higher seas, to see how much worse the damage could be.
The latest exposure numbers are much larger than the 2015 ones the former Parliamentary Commissioner for the Environment calculated. That’s because Jan Wright’s report took the normal high tide-line and added sea level rise, without looking at what would happen in an extreme storm flood.
As of today, just under 50,000 buildings worth $12.5b could be potentially exposed to an extreme coastal flood — even without any further sea level rise, Bell and Paulik found.
Up to 72,065 people live in these exposed areas — based on the 2013 census — and that number would more than double after 80cm of sea level rise, they discovered.
That’s a population bigger than Nelson whose risks from the sea could change within 60cm.
SOURCE: Newsroom
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