Rising sea levels will boost moderate floods in some areas, severe floods in others

Rising sea levels will boost moderate floods in some areas, severe floods in others
Researchers at Princeton and Rutgers universities found that sea-level rise will boost the number of moderate and severe coastal floods by different amounts based on the location around the country. In the image, which predicts flooding levels 50 years from now under a scenario with no serious reductions in greenhouse gas emissions, the beige and yellow colors mean little amplification of existing flooding episodes, while blue and purple colors mean hundreds to thousands of times more floods. The southeastern city of Charleston, South Carolina, which is subject to more frequent and severe floods than the northwest, will see an increase in the number of moderate floods as shown in the left panel by the green dot, but a smaller increase in the number of severe floods as shown in the right panel by the yellow dot. The northwestern city of Seattle, which currently experiences few severe floods, will experience little amplification of moderate floods as shown in the left panel by the yellow dot, but a larger amplification in severe floods, as shown in the right panel by the green dot. Credit: Maya Buchanan, Princeton University

Rising seas are making flooding more common in coastal areas around the country. Now, a new study finds that sea-level rise will boost the occurrence of moderate rather than severe flooding in some regions of the United States, while in other areas the reverse is true.

The study by researchers at Princeton and Rutgers universities found that along the southeastern coast, where severe flooding due to hurricanes is relatively frequent, cities such as Charleston, South Carolina, will see a disproportionate increase in moderate flooding. However, areas that have little history of severe flooding, such as Seattle, are likely to experience a greater uptick in the number of severe, or even historically unprecedented, floods.

The study, published June 7 in the journal Environmental Research Letters, looked at how climate-driven rise is likely to amplify coastal flooding—which already costs municipalities along the East and Gulf coasts $27 billion annually—over the next 50 to 100 years.

Improving the accuracy of flooding estimates is important as coastal cities and states take actions to protect themselves against future storms, according to Michael Oppenheimer, Princeton's Albert G. Milbank Professor of Geosciences and International Affairs. "To make these decisions, local governments need an understanding of the frequency with which extreme floods will return in the future," Oppenheimer said. "A key element is getting the science right, and that was our main objective in this study."

The researchers sought to improve the accuracy of a set of predictions included in a 2013 Intergovernmental Panel on Climate Change (IPCC) report. That analysis did not consider the possibility that sea-level rise might amplify some levels of flooding more than others.

"Treating the change in flood risk due to sea-level rise as the same at all levels of flooding oversimplifies the flood hazard characterization and could lead to costly policy missteps," said Maya Buchanan, the first author on the study and a doctoral student in Princeton's Woodrow Wilson School of Public and International Affairs.

The new study combined historical data on flood-heights collected at tide gauges with estimates of local sea-level changes developed previously by study co-author Robert Kopp, professor of earth and planetary science at Rutgers, and other colleagues.

Sea level is an important factor in the frequency and amount of because even modest increases can cause floods to inundate larger areas of land, or submerge areas more deeply. "For example, to produce a six-foot flood," Kopp said, "if the ocean is a foot higher, you only need as much storm surge as you would have previously needed to produce a five-foot flood."

The researchers calculated the "amplification factor"—the amount by which a given rise in sea level drives the increase in the number of floods—for numerous locations around the country. "The amount of sea-level rise that occurs will change the number of both moderate and severe floods," Buchanan said. "Climate change-driven sea-level is usually thought of as slow and steady, but actually a relatively small amount of increase in sea level can amplify the flood level significantly."

The study suggests that cities like Seattle will need to prepare for largely unprecedented, severe flooding, while other areas may need to prepare especially for more common but less severe events. For example, if current carbon emissions continue, by 2050 a moderate flood—of the size that historically has occurred approximately every ten years—would recur 173 times more often in Charleston but only 36 times more often in Seattle. A severe flood, defined as occurring about once every 500 years, would happen six times as often in Charleston but 273 times as often in Seattle.

"We hope that this study provides additional information that cities and municipalities can use to start planning the defense against and ," said Oppenheimer, who serves as an adviser on the New York City Panel on Climate Change. "This is especially important as federal programs for planning for climate adaptation are on the chopping block." Oppenheimer and Kopp were also authors of the most recent report of the IPCC.


Explore further

Rising seas set to double coastal flooding by 2050: study

More information: Maya K Buchanan et al, Amplification of flood frequencies with local sea level rise and emerging flood regimes, Environmental Research Letters (2017). DOI: 10.1088/1748-9326/aa6cb3
Journal information: Environmental Research Letters

Citation: Rising sea levels will boost moderate floods in some areas, severe floods in others (2017, June 7) retrieved 19 June 2019 from https://phys.org/news/2017-06-sea-boost-moderate-areas-severe.html
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Jun 07, 2017
Weird, I thought our coastlines were supposed to already be several feet underwater. It's weird that all these eco-disaster predictions turn up false and are then memory-holed just in time for a new prediction.

Jun 07, 2017
The vast majority of damaging floods occurs INLAND, not along the coast.

How many coastal areas do any of you know that are going to be flooded because of, for example, a 2 inch rise in the ocean level? Personally, I know of none.


Jun 07, 2017
Weird, I thought our coastlines were supposed to already be several feet underwater. It's weird that all these eco-disaster predictions turn up false and are then memory-holed just in time for a new prediction.

Yes, I agree. They predicted by 2010 the Maldive island chain would be underwater. I will believe it when their predictions come true more than at least 60% of the time and on time without constantly re-tweaking the computer forecaster.

Jun 07, 2017
Who knew that Chicken Little would be the head of a 2.5 billion dollar per year organized science fraud ring.

Jun 07, 2017
I ask you, just how many climate scientists does the world need? I appears that we have way too many doing useless research. The US educational system should be held accountable for this hoax.

Jun 08, 2017
Generally speaking, the coastline is defined as the boundary between the water and the land. How can part of it "be under water"? I can see perhaps that at low tide for example, more land is exposed, and visa vs for high tide, but the comment is clearly meaningless when taken in context.

I am astonished that people do not understand that tidal surges caused by a combination of tides and rising sea levels do not have to be planned for, else they cause enormous damage. The storm surge damage caused by hurricane Sandy in NYC is still being paid for.

Making predictions is fraught with difficulties when trying to predict exact numbers. However in this case, scientists are predicting relative dangers rather than exact ones. Showing the Seattle for example is in much larger danger from surges is quite valuable, because the lack of hurricanes in that area means that many of the seawalls and other protections where those types of storms occur are not present.

Jun 08, 2017
@Bart_A - as a rough guide, on the average every inch of sea level rise results in the horizontal spread of 100 inches laterally. Some places of course this spread is 0 (when blocked by a vertical rise for example), other places its much more, this is considered an average.

But the effects of sea level rises are not usually noticed except during storms. At that time the effects of a few inches are magnified.

Jun 08, 2017
Sorry but the effects of rising seas are pretty much masked by coastal storms. The people in these areas are made well aware of their situation multiple times of year. They don't need a computer model t tell them that their roads flood and their basements are under water. Pretty much everyone on the east coast knew that Sandy was just of matter of when and not if.

Jun 08, 2017
How many coastal areas do any of you know that are going to be flooded because of, for example, a 2 inch rise in the ocean level? Personally, I know of none.

The article is about sea level rise in 50 - 100 years from now, so they're talking about feet, not inches.

As far as a 2 inch rise causing flooding, anyplace that's having problems right now would have much more severe problems with an additional 2 inches. Some areas of the US already need to deal with sea level rise, like Atlantic City and south Florida (https://www.thegu...vel-rise ). Combined with the observed increase in hurricane strength, the current sea level rise is already a problem and costs hundreds of millions of dollars (on a losing cause, I think). And that's just the US.

All of this has been extensively in the news, so if you're not aware of it perhaps you should stop avoiding reality and join life.

Jun 08, 2017
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Jun 08, 2017
Only part of the continent rises, Dingbat.

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