Danger for New York: The risk of storm surges like Hurricane Sandy is already three times higher for New York than it was 200 years ago. By the year 2100, such floods could become several times more frequent, as climate researchers have determined. The rising sea level alone is making the metropolis more susceptible to storm surges, they report in the specialist journal “Proceedings of the National Academy of Sciences”.
The record storm “Sandy” is still considered to be one of the greatest weather disasters in US history. In the fall of 2012, this hurricane moved up the US east coast and triggered violent storm surges. Large parts of New York also sank in the floods. Sandy left $ 71 billion in damage and killed 157 people. For New York, such a storm surge with levels of up to 2.80 meters above normal was previously an absolute exception.
But what about the future? Ning Lin of Princeton University and his colleagues have now examined the current and future risk of storm surges in New York in more detail. For their study, they evaluated data on past and future sea level rise and combined this with forecasts of various climate models on the frequency of storm surges.
Risk tripled now
The result: In 1800 flood heights like Sandy were still a real “millennium event” for New York: they only occurred on average every 1,200 years, as the researchers report. By the year 2000, however, the risk of such storm surges had already tripled – and that was solely due to the rise in sea levels. A change in the frequency of storms was not yet taken into account here.
Flooded Manhattan road tunnel after Hurricane Sandy © Metropolitan Transportation Authority of the State of New York
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According to Lin and his colleagues, sea levels in the New York area rose by around 50 centimeters from 1800 to 2000 – far more than the global average of around 15 centimeters. This is due, among other things, to changes in glacier ice in the Arctic, but also to ocean currents and local effects.
“The situation will get worse”
But it looks even worse for the future: “The situation will get even worse by 2100,” says co-author Benjamin Horton of Rutgers University. “Even if nothing changes during the hurricanes, storm surges like Sandy will become more frequent just because of the rise in sea level.”
As the simulations showed, the flood risk increased by a factor of 4.4 by 2011 compared to today. Exceptional floods of 2.80 meters above normal then occur on average every 90 years. “Sandy” will then no longer even turn from a “millennium event” into a “storm surge of the century”.
New York subway tunnel in December 2012 – it took months to repair the flood damage. © Metropolitan Transportation Authority of the State of New York
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More hurricanes in the north
The situation could become much more dramatic if the strength, frequency and trajectory of hurricanes change in the future. In fact, climate models indicate that tropical cyclones could migrate to higher latitudes more frequently in the future. At the same time, the total number of hurricanes is not supposed to increase, but their intensity is.
If the researchers factored in these prognoses, New York’s risk of Sandy-like storm surges increased by a factor of three to 17. “According to this, severe storm surges will likely become more frequent in the future,” says Lin. However, there is still great uncertainty about how strong this change will be.
Help for future flood protection
The results should help authorities and civil protection experts to assess the specific risk and the necessary protective measures for New York. The US Department of Urban Development is already planning to protect Manhattan from future storm surges with additional walls and buffer zones.
“To prepare effectively for future hurricanes, we need to know what is in store for coastal cities in the decades to come,” says Lin. “You need concrete figures to plan and our analysis provides a quantitative basis for the effects of sea level rise and storm surge climatology.” (Proceedings of the National Academy of Sciences, 2016; doi: 10.1073/pnas.1604386113)
(Princeton University/ PNAS, 11.10.2016 – NPO)
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