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Planning for Changing Sea Levels

 
   
 

New Jersey: The simple tool has two steps. First, identify the Base Flood Elevation (BFE) or best available elevation for your location using the FEMA web site. Second, go to the table for New Jersey and enter the BFE/best available elevation. The BFE/best available elevation will be added to the potential future sea levels calculated by NOAA to obtain elevations for consideration in your recovery effort.

New York: Bronx, Brooklyn, Manhattan, Queens, Staten Island: The simple tool has two steps. First, identify the best available elevation for your location using the FEMA web site. Second, go to the table for New York City and enter the best available elevation. The best available elevation will be added to the potential future sea levels calculated by the New York City Panel on Climate Change (NPCC) to obtain elevations for consideration in your recovery effort. The sea level rise projections shown for New York City are based on work of the New York City Panel on Climate Change (NPCC, 20131). These are regionalized projections based on thermal expansion of the ocean, dynamical changes in ocean height, land subsidence, land-water storage, land-based ice loss, and regional responses to land-based ice loss. The projections are for the 2020s and 2050s, relative to the 2000-2004 base period.

New York - Westchester County: The simple tool has two steps. First, identify the BFE/best available elevation for your location using the FEMA web site. Second, go to the table for New York – Westchester County and enter the BFE/best available elevation. The BFE/best available elevation will be added to the potential future sea levels calculated by NOAA to obtain elevations for consideration in your recovery effort.

How Do I Use This Information?

Let’s assume you have selected New Jersey, 1% BFE/best available elevation is 11 ft.  Your simple table looks like the one below.

Graphic of Simple Table

Your first question might be “Why are there four curves to choose from? Why can’t you just give me a number?”

The detailed answer to that question can be found in the NOAA report. But that’s a very long and detailed science report, and not everyone will have the time or knowledge to read and interpret the report.

Even if you simply look at the Executive Summary (pdf), you will see the following statement:

“We have very high confidence (>9 in 10 chance) that global mean sea level will rise at least 0.2 meters (8 inches) and no more than 2.0 meters (6.6 feet) by 2100.”

What the report basically says is that it is not possible to accurately project future sea levels and their associated tides and surges.

Looking at the numbers in the table, you can see that the elevations for the Low to High curves are closer together in the near future, but then get farther apart the farther out in time you look.

Different people might consider different time periods, depending on their personal investments and how much risk they are willing to take. So looking at the results from the different curves can help you make decisions, even if you don’t simply have one number to evaluate.

For example, let’s also assume that your community is going to be moving to BFE/best available elevation plus freeboard of 2 ft. In this case, you’d be looking at elevating or floodproofing to elevation 13 ft (or higher).

The way to evaluate the table results is to look for where the values in the table are less than or equal to 13 ft. These are marked with red circles on the table below. 

Graphic of Simple Table with illustrations

If you then look across from the red circles to the dates, you’ll see an expected date at which the combined effects of the processes that drive the BFE/best available elevation and changing sea levels may result in flooding.

So this tells us that if changing sea levels approximately follow the Intermediate-Low curve, elevating or floodproofing to elevation 13 ft will be robust to about 2090.

If sea levels rise faster, more like the Intermediate-High curve, elevating or floodproofing to elevation 13 ft will be robust to about 2060.

On the other hand, if sea level rise begins accelerating, to something approximating the High curve, elevating or floodproofing to elevation 13 ft will be robust to about 2045, or just a couple of years after the end of a 30-year mortgage started today.

You can make the same kind of analysis using the simple table for your location and with a few different BFE/best available elevation values (BFE/best available elevation, BFE/best available elevation plus 1 ft freeboard, BFE/best available elevation plus 2 ft freeboard) to assess for yourselves how the future risks might impact your decisions today.


1 New York City Panel on Climate Change, 2013: Climate Risk Information 2013: Observations, Climate Change Projections, and Maps. C. Rosenzweig and W. Solecki (Editors), NPCC2. Prepared for use by the City of New York Special Initiative on Rebuilding and Resiliency. New York, NY.

Photo of Long Beach Island after Hurricane Sandy

Long Beach Island

Photo of Breach at Mantoloking, NJ

Breach at Mantoloking, NJ