Introduction | Methods and Qualifiers | Data Layers | Sources | Services | Team | Special Thanks | Site Credits | Legal

Introduction

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 in some locations, and Climate Central’s more accurate CoastalDEM in others (see Methods and Qualifiers). 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, CBS, 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.

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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).

Areas using lidar-based elevation data: U.S. coastal states except Alaska

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)).



Areas using CoastalDEM™ elevation data: Antigua and Barbuda, Barbados, Corn Island (Nicaragua), Dominica, Dominican Republic, Grenada, Guyana, Haiti, Jamaica, Saint Kitts and Nevis, Saint Lucia, Saint Vincent and the Grenadines, San Blas (Panama), Suriname, The Bahamas, Trinidad and Tobago.



CoastalDEM™ is a proprietary high-accuracy bare earth elevation dataset developed especially for low-lying coastal areas by Climate Central. Use our contact form to request more information.

Warning for areas using other elevation data (all other areas)

Areas of this map not listed above 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.

Error

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.

Connectivity

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 areas using lidar-based elevation data or CoastalDEM (see above), elevation data is accurate enough that non-connected areas can be clearly identified and treated separately in analysis (these areas are colored green on the map). In the U.S., levee data are complete enough to factor levees into determining connectivity as well. However, in other areas, 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, in these regions, 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).

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Data Layers

Water Level

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.

Projections

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 two recent peer-reviewed research papers (Kopp et al. 2014; Kopp et al. 2017) building off of global projections from the IPCC and, in the latter case, new research on the potential instability of Antarctic ice sheets (DeConto and Pollard 2016).

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 other 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).

Legend

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.)

Population (where shown)

Data sources vary as follows:

Census: U.S. (U.S. Census); Nassau, The Bahamas (Government of The Bahamas Department of Statistics)

WorldPop 100m resolution data:

Antigua and Barbuda

Dominican Republic

Guyana

Haiti

Jamaica

Corn Islands (Nicaragua)

San Blas Islands (Panama)

Suriname

Trinidad and Tobago

LandScan 1km resolution data:

The Bahamas

Barbados

Dominica

Grenada

St. Kitts and Nevis

St. Lucia

St. Vincent and the Grenadines

Internet Infrastructure

Count of wireless routers (WiFi sources) and cellphone towers on a 100m grid. May be considered an indicator of economic wealth or activity. Data source: Skyhook

Ethnicity (U.S.)

U.S. Census definitions used. Census block resolution data. Data source: U.S. Census

Income (U.S.)

Per capita income. Census tract resolution data. Data source: U.S. Census

Property (U.S.)

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.

Landmarks (U.S.)

Data sources: U.S. Department of Transportation

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Sources

See Data Layers, above, for most sources. Others follow.

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Services

Learn about Climate Central’s portfolio analytics, global coastal elevation data, custom analysis and tool-building for clients with more specialized needs.

Team

The Climate Central sea level rise group conceived and maintains this tool. Please consider supporting our nonprofit efforts.

Special Thanks

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, Island Foundation, and others. 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.

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Site Credits

Map designed and built in collaboration with Stamen Design in San Francisco.

Icons (U.S.)

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General Disclaimer & Legal Terms

The purpose of our web tools is to provide local regions and policy makers with the tailored local information they need to understand and respond to the risks of sea level rise and coastal flooding. Our web tools are screening/scoping tools that use consistent data sets and analyses at the national level within the U.S., and a different consistent set across all other nations outside the U.S. For information visit Disclaimer | Terms of Use

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