The Areas Vulnerable to Coastal Flooding and Sea-Level Rise data set is prepared by Climate Central. These layers are relative to local high tide lines (mean higher high water, or MHHW). Map areas below the selected water level are displayed in blue, indicating vulnerability to flooding from combined sea-level rise, storm surge, and tides, or to permanent submergence by long-term sea-level rise. Elevation data used for parts of this map within the United States come almost entirely from ~5 m horizontal resolution digital elevation models curated and distributed by the National Oceanic and Atmospheric Administration in its Coastal Lidar collection, derived from high-accuracy laser-rangefinding measurements. Areas outside the United States use elevation data on a roughly 90 m horizontal resolution grid derived from the National Aeronautics and Space Administration’s Shuttle Radar Topography Mission (SRTM). Local high tide level is determined using 2 data sources as well: the VDatum tidal model for the contiguous United States and a global tidal model supplied by Mark Merrifield of the University of Hawaii for the rest of the world.
Projections of SLR linked to Climate Scenarios
The SRTM provides surface, rather than bare-earth, elevations, causing it to commonly overestimate elevation, especially in areas with dense and tall buildings or vegetation. While the SRTM contains significant error in both directions, depending on location, the map more often underportrays areas that could be submerged at each water level, and exposure is usually greater than shown (Kulp and Strauss 2016). The SRTM does not cover latitudes above 60°N or below 56°S, meaning that sparsely populated parts of Arctic Circle nations are not assessed here. Areas of this map in Alaska use elevation data on a roughly 60 m horizontal resolution grid supplied by the U.S. Geological Survey. These data are 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. This data set does not indicate where certain areas of low-elevation land are protected from sea-level rise by local topographical features, such as being surrounded by higher land that will not allow rising seas to seep through. Similarly, these data do not indicate whether an area of land is protected from sea-level rise through built infrastructural mitigations such as levees, seawalls, or other structures. Analysis does not consider erosion, marsh migration, porous bedrock geology, channels, holes, or passages for drainage, or other connectivity features not revealed in the elevation data.
Climate Central, Surging Seas, sealevel.climatecentral.org 2018. Accessed through Resource Watch, (date). www.resourcewatch.org.
Contiguous US + Hawaii: almost entirely 5m or better horizontal resolution. ⅓ arcsec resolution (~10m) in areas where NOAA Coastal lidar is not available Alaska: Approximately 60-meter horizontal resolution Outside US: 3 arcsecond (90m)
NOAA Coastal Lidar: SRTM: 2000 VDatum: 2012 Merrifield MHHW: 2015