Introduction | Methods and Qualifiers | Levees and Dams | Definitions | Sources | Special Thanks | Site Credits | Legal
Sea level rise means more and higher floods.
Climate Central’s Submergence Risk Map shows areas vulnerable to flooding from combined sea level rise, storm surge, and tides, or to permanent submersion by long-term sea level rise. It incorporates the latest, high-resolution, high-accuracy lidar elevation data supplied by NOAA, displays points of interest, and contains layers displaying social vulnerability, population density, and property value. It provides the ability to search by location name or zip code.
The accompanying Risk Finder is an interactive data toolkit that provides local projections and assessments of exposure to sea level rise and coastal flooding tabulated for every zip code and municipality along with planning, legislative and other districts. Exposure assessments cover over 100 demographic, economic, infrastructure and environmental variables using data drawn mainly from federal sources, including NOAA, USGS, FEMA, DOT, DOE, DOI, EPA, FCC and the Census. The three components of the Risk Finder can be accessed via links in the upper right hand corner of this map.
This web tool was recently highlighted at the launch of The White House's Climate Data Initiative. Climate Central's original Surging Seas was featured on NBC, CBS, and PBS national news, the cover of The New York Times, in hundreds of other stories, and in testimony for the U.S. Senate. The Atlantic Cities named it the most important map of 2012. The Submergence Risk Map and the Risk Finder apply methods from the same peer-reviewed science to new and improved data. Climate Central is developing these tools for all coastal U.S. states.
Methods and Qualifiers
Map elevation data come almost exclusively from high-accuracy laser (lidar) measurements. For all areas and elevations covered by NOAA’s Sea Level Rise Viewer, Surging Seas Submergence Risk Map uses the same base data. In our tests, the two maps have a 95% or better match between 0 and 6 ft above high tide (6 ft is the max height in the Viewer). Water level means feet above the local high tide line. Water can reach any level at different times through different combinations of sea level rise, tide and storm surge.
Employing elevation relative to local high tide lines (Mean Higher High Water, or MHHW), this analysis uses near-flat water surfaces statewide to compare exposure. Actual storms create uneven flooding in limited areas.
Levees and Dams
Levees, walls, dams or other features may protect some areas, especially at lower elevations. Data limitations, such as incomplete levee data, make assessing protection difficult. For example, this may be an issue in the Boston area, where certain dams stand 6.8 ft above Mean Higher High Water (MHHW), but are shown protecting Cambridge and other areas only up to 4 ft in this mapping analysis, due to alternate pathways for flow indicated by the elevation data.
For analysis, mapped levees are assumed high and strong enough for flood protection. However, we have no data on levee height, and only 8% of monitored levees in the U.S. are rated in “Acceptable” condition (ASCE).
The main source used, the Midterm Levee Inventory (FEMA/USACE), is the best available national levees dataset, but is incomplete. However, the Surging Seas Submergence Risk Map implicitly also includes unmapped levees captured directly by elevation data.
Note: Areas displayed as Isolated Areas on the map may be connected to water via porous bedrock geology, and also may also be connected via channels the elevation data fails to pick up, due to error or limited resolution. In addition, sea level rise may cause problems in isolated low zones during rainstorms by reducing drainage and creating backups into wastewater treatment facilities.
Errors in elevation data, missing levees, and levees in poor repair may all lead to some land being misclassified among the Area categories. Furthermore, this analysis does not account for future erosion, marsh migration, or construction. As is general best practice, local detail should be verified with a site visit. Sites located in zones below water level may or may not be subject to flooding at that level. This map and analysis takes into account only the elevation of the land that structures rest upon, and not the basement or floor elevations of structures relative to the land.
For more information, visit Science Behind the Tool or read an example of one of our reports.
For more information on how Surging Seas incorporates levees and elevation data in Louisiana, view our Louisiana levees and DEMs methods PDF.
Definitions & Legend
- Water level: Height relative to the local high tide line (“Mean Higher High Water”), instead of standard elevation.
- Social vulnerability: The ability of communities to prepare and respond to hazards like flooding; based on Hazards and Vulnerability Research Institute (HVRI)’s Social Vulnerability Index. “High” and “low” indicate the 20% most and least vulnerable in coastal areas of each state.
- Income: Per capita income.
- Direct Risk Areas: Areas below water level, and connected to the ocean.
- Isolated Areas: Areas below water level, but not connected to the ocean, due to natural or built breaks such as levees. View technical notes below for more information.
- Dry Areas: Areas above water level.
- Levees: Built flood control structures.
- Elevation: National Oceanic and Atmospheric Administration (NOAA), U.S. Geological Survey (USGS)
- Tidal elevation: NOAA
- Levees: U.S. Army Corps of Engineers (USACE), Pacific Institute
- Social vulnerability: Hazards and Vulnerability Research Institute (HVRI)
- Features: U.S. Department of Transportation, U.S. Federal Rail Administration, U.S. Department of Education, U.S. Energy Information Administration, U.S. Environmental Protection Agency, U.S. Federal Communications Commission, U.S. Board of Geographic Names / U.S. Geological Survey, NJ OIT/OGIS, NJ HSIP, National Center for Education Statistics.
- Population, Ethnicitiy, Housing, Income: U.S. Census
- Property Value: U.S. Environmental Protection Agency (EPA)
- Map tiles by Stamen Design, under CC BY 3.0. Data by OpenStreetMap, under CC BY SA.
To our project partner for social vulnerability analysis, the University of South Carolina Hazards and Vulnerability Research Institute.
To NOAA’s Office for Coastal Management, which has provided high-accuracy coastal elevation data, consistent courtesy, and leadership with its Sea Level Rise Viewer and Coastal Flood Exposure Mapper – mapping tools Surging Seas strives to complement.
To officials at the Environmental Protection Agency (EPA) and the Federal Communications Commission (FCC), who provided guidance regarding their extensive public geospatial datasets.
To Climate Central’s financial supporters for this project: The Schmidt Family Foundation, The Kresge Foundation, The Rockefeller Foundation, and Island Foundation.
To Stamen, for developing the second generation Surging Seas mapping interface.
To Bocoup, for developing the Surging Seas Risk Finder data visualization interface.
Submergence risk mapping site designed and built by Stamen Design in San Francisco.
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