Introduction | Methods and Qualifiers | Data Layers | Sources | Services | Team | Special Thanks | Site Credits | Legal
Climate Central’s Surging Seas: Risk Zone map shows areas vulnerable to near-term flooding from different combinations of sea level rise, storm surge, tides, and tsunamis, or to permanent submersion by long-term sea level rise. Within the U.S., it incorporates the latest, high-resolution, high-accuracy lidar elevation data supplied by NOAA (exceptions: see Sources), displays points of interest, and contains layers displaying social vulnerability, population density, and property value. Outside the U.S., it utilizes satellite-based elevation data from NASA. It provides the ability to search by location name or postal code.
The accompanying Risk Finder is an interactive data toolkit available for some countries
that provides local projections and assessments of exposure to sea level rise and coastal flooding tabulated
for many sub-national districts, down to cities and postal codes in the U.S. Exposure assessments always
include land and population, and in the U.S. extend to 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.
This web tool was highlighted at the launch of The White House's Climate Data Initiative in March 2014. Climate Central's
original Surging Seas was
featured on NBC,
and PBS U.S. 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.
Both the Risk Zone map and the Risk Finder are grounded in peer-reviewed science.
Back to top
Methods and Qualifiers
This map is based on analysis of digital elevation models mosaicked together for near-total coverage of the
global coast. Details and sources for U.S. and international data are below. Elevations are transformed so
they are expressed relative to local high tide lines (Mean Higher High Water, or MHHW). A simple elevation
threshold-based “bathtub method” is then applied to determine areas below different water levels, relative
to MHHW. Within the U.S., areas below the selected water level but apparently not connected to the ocean at
that level are shown in a stippled green (as opposed to solid blue) on the map. Outside the U.S., due to data
quality issues and data limitations, all areas below the selected level are shown as solid blue, unless
separated from the ocean by a ridge at least 20 meters (66 feet) above MHHW, in which case they are shown
as not affected (no blue).
Elevation data used for parts of this map within the U.S. come almost entirely from ~5-meter horizontal
resolution digital elevation models curated and distributed by NOAA in
its Coastal Lidar collection,
derived from high-accuracy laser-rangefinding measurements. The same data are used in
NOAA’s Sea Level Rise Viewer.
(High-resolution elevation data for Louisiana, southeast Virginia, and limited other areas comes from
the U.S. Geological Survey (USGS)).
Elevation Warnings (Global and Alaska)
Areas of this map outside the U.S. use elevation data on a roughly 90-meter horizontal resolution grid
derived from NASA’s Shuttle
Radar Topography Mission (SRTM). SRTM provides surface elevations, not bare earth elevations, causing
it to commonly overestimate elevations, especially in areas with dense and tall buildings or vegetation.
Therefore, the map under-portrays areas that could be submerged at each water level, and exposure
is greater than shown (Kulp and Strauss, 2016). However, SRTM includes
error in both directions, so some areas showing exposure may not be at risk.
SRTM data do not cover latitudes farther north than 60 degrees or farther south than 56 degrees, meaning
that sparsely populated parts of Arctic Circle nations are not mapped here, and may show visual artifacts.
Areas of this map in Alaska use elevation data on a roughly 60-meter horizontal resolution grid supplied by
the U.S. Geological Survey (USGS).
This data is referenced to a vertical reference frame from 1929, based
on historic sea levels, and with no established conversion to modern reference frames. The data also do not
take into account subsequent land uplift and subsidence, widespread in the state. As a consequence, low
confidence should be placed in Alaska map portions.
Flood control structures (U.S.)
Levees, walls, dams or other features may protect some areas, especially at lower elevations. Levees and
other flood control structures are included in this map within but not outside of the U.S., due to poor and
missing data. Within the U.S., data limitations, such as an incomplete inventory of levees, and a lack of
levee height data, still make assessing protection difficult. For this map, levees are assumed high and
strong enough for flood protection. However, it is important to note that only 8% of monitored levees in
the U.S. are rated in “Acceptable” condition (ASCE). Also note that the map implicitly includes unmapped
levees and their heights, if broad enough to be effectively captured directly by the elevation data.
For more information on how Surging Seas incorporates levees and elevation data in Louisiana, view our
Louisiana levees and DEMs methods PDF.
For more information on how Surging Seas incorporates dams in Massachusetts, view the Surging Seas column of
the web tools comparison matrix for Massachusetts.
Errors or omissions in elevation or levee data may lead to areas being misclassified. 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 a given water level may or
may not be subject to flooding at that level, and sites shown as isolated may or may not be be so. Areas
may be connected to water via porous bedrock geology, and also may also be connected via channels, holes,
or passages for drainage that the elevation data fails to or cannot pick up. In addition, sea level rise
may cause problems even in isolated low zones during rainstorms by inhibiting drainage.
At any water height, there will be isolated, low-lying areas whose elevation falls below the water level,
but are protected from coastal flooding by either man-made flood control structures (such as levees), or
the natural topography of the surrounding land. In the U.S., elevation data is detailed enough, and levee
data complete enough, that non-connected areas can be clearly identified and treated separately in analysis
(these areas are colored green on the map).
However, outside of the U.S., elevation data is much less accurate, and noisy error often produces “speckled”
artifacts in the flood maps, commonly in areas that should show complete inundation. Removing non-connected
areas in these places could greatly underestimate the potential for flood exposure. For this reason,
outside of the U.S., the only areas removed from the map and excluded from analysis are separated from the
ocean by a ridge of at least 20 meters (66 feet) above the local high tide line, according to the data, so
coastal flooding would almost certainly be impossible (e.g., the Caspian Sea region).
Back to top
| Social Vulnerability
Water level means feet or meters above the local high tide line (“Mean Higher High Water”) instead of standard elevation. Methods described above explain how each map is generated based on a selected water level. Water can reach different levels in different time frames through combinations of sea level rise, tide and storm surge. Tide gauges shown on the map show related projections (see just below).
The highest water levels on this map (10, 20 and 30 meters) provide reference points for possible flood risk from tsunamis, in regions prone to them.
Scientists agree that climate change has been driving a rise in global sea level, and the rise will
accelerate, leading to ocean intrusion on land and aggravated coastal flood risk. Over 1,000 global
tide gauges shown on the map, illustrated by bulls-eyes, give downloadable local projections for sea level
rise through the year 2200, based on recent peer-reviewed
research (Kopp et al. 2014) building off of global
projections from the IPCC. Select tide
gauges within the U.S. where at least 30 years of hourly water level
data are available also give flood risk projections which integrate sea level rise, based on methods
described in more recent research
(Tebaldi et al. 2012; Buchanan et al. 2016).
Outside the U.S., flood risk forecasts are based upon integrating sea level projections with flood risk statistics from the Global Tide
and Surge Reanalysis (Muis et al. 2016). In
all cases, users may select from among different carbon pollution scenarios,
including “unchecked pollution” (technically, Representative Concentration Pathway
8.5, or RCP 8.5), “moderate carbon cuts” (RCP 4.5), and “extreme carbon cuts” (RCP 2.6), this last choice meaning
a peak in emissions near the year 2020 followed by a sharp decline to zero near 2070. For gauges with flood
risk projections, users may choose between viewing accrued risk (i.e. what is the multi-year risk of
flooding between the present and a future year) or annual risk (i.e. what is the single-year risk of
flooding within the indicated future year).
Below water level: Areas below water level, and connected to the ocean.
Below but isolated: Areas below water level, but not connected to the ocean, due to natural or built breaks such as levees. This type of area is separately identified only within the U.S., where higher quality elevation data and the availability of levee data allow greater confidence in the assessment of connectivity. See Methods for more detail.
Levees: Built flood control structures including dams, gates and surge barriers as well as levees.
Tide gauges: Locations with long-term water level records sufficient for making localized sea level projections and, in cases, flood risk projections.
Social Vulnerability (U.S.)
This map defines social vulnerability as the ability of communities to prepare and respond to hazards like flooding. "High" and "low" indicate the 20% most and least vulnerable in coastal areas of each state. Census tract resolution data. Data source: Hazards and Vulnerability Research Institute (HVRI)'s Social Vulnerability Index. (Map layer currently available only within the U.S.)
Census block resolution data. Data source: U.S. Census
U.S. Census definitions used. Census block resolution data. Data source: U.S. Census
Per capita income. Census tract resolution data. Data source: U.S. Census
Census block group resolution data. Based mostly on assessed values in 2008, adjusted to 2012 dollars.
Data sources: U.S. Environmental Protection Agency, Neumann et al 2011.
Data sources: U.S. Department of Transportation
, U.S. Energy Information Administration
, U.S. Board of Geographic Names / U.S. Geological Survey
, National Telecommunications and Information Administration
, National Center for Education Statistics
Back to top
See Data Layers, above, for most sources. Others follow.
- U.S. elevation data: National Oceanic and Atmospheric Administration (NOAA),
U.S. Geological Survey (USGS) (for Louisiana, southeast Virginia, Alaska, and limited other areas). Global elevation data:
- Global sea surface height data (1993-2009): Aviso.
- U.S. tidal elevation data: NOAA.
- Global tidal elevation data: courtesy of Mark Merrifield, University of Hawaii.
- Global flood risk parameters: courtesy of Sanne Muis, Vrije Universiteit Amsterdam (see Muis et al. 2016).
- Levees (U.S.): Midterm Levee Inventory (FEMA, U.S. Army Corps of Engineers), Louisiana Coastal Protection and Restoration Authority
- Map tiles by Stamen Design, under CC BY 3.0. Data by OpenStreetMap,
under CC BY SA.
Back to top
Learn about Climate Central’s custom analysis and tool-building for clients with more specialized needs.
The Climate Central sea level rise group conceived
and maintains this tool. Please consider supporting our nonprofit efforts.
To the many organizations that have financially supported Climate Central and its sea level program,
including The Schmidt Family Foundation, The Kresge Foundation,
The Rockefeller Foundation,
Map development was also supported in part by U.S. National Science Foundation
grant ARC-1203415, and by the Raising Risk Awareness (RRA) project. RRA is funded by the UK Department
for International Development (DFID) through the Climate and Development Knowledge Network (CDKN), and
by Eric and Wendy Schmidt through Climate Central, Inc. CDKN is a programme funded by DFID and the
Netherlands Directorate-General for International Cooperation (DGIS) for the benefit of developing countries.
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, a map tool Surging Seas strives to complement.
To our project partner for U.S. social vulnerability analysis, the University of South Carolina Hazards and Vulnerability Research Institute.
Back to top
Map designed and built in collaboration with Stamen Design in San Francisco.
- Hospital icon used to represent Hospitals designed by Saman Bemel-Benrud from The Noun Project.
- Badge icon used to represent Fire/EMS/Police stations designed by Edward Boatman from The Noun Project.
- School icon used to represent Schools/Colleges designed by Saman Bemel-Benrud from The Noun Project.
- Prayer icon used to represent Houses of Worship was designed by Carson Wittenberg from The Noun Project.
- Museum icon used to represent Culture/Museums/Arts designed by Unknown Designer from The Noun Project.
- Government Office icon used to represent Government/Community designed by OCHA AVMU from The Noun Project.
- Power Plant icon used to represent Powerplants designed by Iconathon with Collaboration by Chad Williamsen, Katie Williamsen, Alison Harshbarger & John Durkee from The Noun Project.
- Caution icon used to represent EPA-Listed Sites designed by Sam Ahmed from The Noun Project.
Back to top
General Disclaimer & Legal Terms
Back to top