FEMA's New NYC Flood Maps Will Soon Be Out-of-Date

Flooding due to Hurricane Sandy on October 29, 2012. Image by David Shankbone and used under Creative Commons license.  http://www.flickr.com/photos/shankbone/8139664029/

Hurricane Sandy served as a wake-up call for New York and New Jersey -- and the nation--to become better prepared for the impacts of climate change. And, as Sandy illustrated with fearsome efficiency, flooding is among the biggest risks the nation faces from climate change. That's because as the climate warms, sea levels rise while extreme weather and storm surges make floods increasingly likely.

The Federal Emergency Management Agency (FEMA) is the agency tasked with helping evaluate the nation's vulnerability to flooding and storm surges, by providing maps that reflect the best scientific understanding of where flooding is most likely to occur. In doing this, FEMA can help people stay out of harm's way by helping homeowners make informed choices about where they live; cities to make better decisions about where they build critical infrastructure, schools and hospitals; and business owners decide where to set up shop.

But FEMA's flood maps have never accounted for the future impacts of climate change on flood risk. Given that it can take two decades or longer for FEMA to update flood maps for an area, it's important that flood maps start providing a more realistic look at both present and future risk.

In fact, doing so is now required by law. In 2012, Congress passed legislation that required FEMA to factor in future climate risks, as part of the Biggert-Waters Flood Insurance Reform Act. Given the impact of Hurricane Sandy it was hoped that new maps for New York City might be the test case for how to account for sea level rise and climate-related impacts. But when FEMA released updated maps recently, these risks were still not accounted for.

NRDC filed formal comments on the new maps with FEMA today, raising the fact that FEMA did not factor in future sea level rise and other climate factors, as it is now required to do. Our analysis also shows that the past decade or so of sea level rise (about 2-3 inches) was not accounted for in the maps, nor were the computer models calibrated against data from Sandy. Instead they were calibrated to earlier, less extensive floods. While the new maps are a big improvement over the previous ones, there are areas inundated by Sandy that still lie outside the newly mapped 100- or 500-year flood plains - and the impact of sea level rise on future flood risk isn't accounted for at all.

When Hurricane Sandy flooded parts of New York City many residents never expected to be underwater because flood maps did not show their neighbored as being in the danger zone. In the aftermath, it became all too clear how out of date FEMA's maps of flood zones were, having left communities in the dark about the risks they actually faced, as illustrated in the image below.

sandy flooding.png

Areas flooded by Sandy (red) far exceeded the flood plain delineated on FEMA's flood maps. These maps had been digitized in 2007, but the underlying data had not been updated since 1983.

We will likely find that FEMA's newly proposed maps are similarly obsolete in coming years. As sea levels continue to rise, the areas susceptible to flooding will also increase. The New York Department of State, using data from FEMA's new flood maps and storm modeling data from the National Oceanic and Atmospheric Administration, assembled an interesting set of Risk Assessment Maps that show how flood risks change in response to sea level rise. Below is a comparison between those maps and FEMA's.


The new 100-year floodplain mapped by FEMA (blue area) is significantly smaller than the area at risk of flooding assuming 3 feet of sea level rise or the surge from a category 3 hurricane (Sandy was barely a category 1 storm). FEMA is supposed to factor sea level rise and other climate impacts into its revised flood maps. Composite image based on maps from FEMA and New York Dept. of State.

As you can see, the area at risk in the future is far more extensive than FEMA's new maps indicate. We may not feel the impacts of this in the short-term, but the last maps were not updated for 30 years. If New York has to wait another 30 years, FEMA's proposed maps seriously underestimate the risk of flooding for New York City.

New York City is not alone. All across the country, river and coastal flood maps are woefully out of date. New Yorkers know firsthand the importance of making sure FEMA's updated maps reflect real flooding risks. We are counting on the agency to revisit their updated maps and give New Yorkers -- and ultimately the entire nation -- a real assessment of what's at stake, and how to better prepare for the future.


FEMA responded in January 2015 to the comments NRDC submitted on its proposed flood maps for both New York City and Sandy affected counties in New Jersey. Copies of those responses are below.