(File GDB and ArcGIS LYR and LYRX files, 225 MB)
Originally published by NOAA in June 2019 and modified by MassGIS
The purpose of the Sea Level Rise and Coastal Flooding Impacts Viewer is to provide coastal managers and scientists with a preliminary look at sea level rise and coastal flooding impacts.
Sea Level Inundation
These polygon data depict the potential sea level rise inundation of coastal areas resulting from a projected 1 to 10 feet rise in sea level above current Mean Higher High Water (MHHW) conditions. Although the water surface mapped represents a particular increase in sea level in feet above MHHW, the actual cell values in NOAA's original raster data represent depth in meters.
The layer name for the SLR inundation data is NOAA_SLR_MA_POLY.
Mapping Confidence Data
NOAA also published layers that depict the mapping confidence of the associated SLR inundation data, for the sea level rise amount specified (MHHW up to 10 feet). Areas that have a low degree of confidence, or high uncertainty, represent locations that may be mapped correctly (either as inundated or dry) less than 8 out of 10 times. Areas that have a high degree of confidence, or low uncertainty, represent locations that will be correctly mapped (either as inundated or dry) more than 8 out of 10 times or that there is an 80 percent degree of confidence that these areas are correctly mapped.
The NOAA Office for Coastal Management has tentatively adopted an 80 percent rank (as either inundated or not inundated) as the zone of relative confidence. The use of 80 percent has no special significance but is a commonly used rule of thumb measure to describe economic systems (Epstein and Axtell, 1996). In short, the method includes the uncertainty in the LiDAR-derived elevation data (root mean square error, or RMSE) and the uncertainty in the modeled tidal surface from the NOAA VDATUM model (RMSE). This uncertainty is combined and mapped to show that the inundation depicted in this data is not really a hard line, but rather a zone with greater and lesser chances of getting wet.
MassGIS distributes these 11 raster datasets as NOAA_MA_CONF<#>FT.
Sea Level Inundation
These data illustrate the scale of potential flooding, not the exact location, and do not account for erosion, subsidence, or future construction. Inundation is shown as it would appear during the highest high tides (excludes wind driven tides) with the sea level rise amount. These data should be used only as a screening-level tool for management decisions. As with all remotely sensed data, all features should be verified with a site visit. The dataset is provided "as is," without warranty to its performance, merchantable state, or fitness for any particular purpose. The entire risk associated with the results and performance of this dataset is assumed by the user. This dataset should be used strictly as a planning reference and not for navigation, permitting, or other legal purposes.
Mapping Confidence Data
These data should be used only as a screening-level tool for management decisions. As with all remotely sensed data, all features should be verified with a site visit. The dataset is provided as is, without warranty to its performance, merchantable state, or fitness for any particular purpose. The entire risk associated with the results and performance of this dataset is assumed by the user. This dataset should be used strictly as a planning reference and not for navigation, permitting, or other legal purposes.
he process NOAA used to produce the SLR inundation data can be described as a modified "bathtub approach" that attempts to account for both local/regional tidal variability as well as hydrological connectivity. The process uses two source datasets to derive the final inundation rasters and polygons and accompanying low-lying polygons for each iteration of sea level rise: the Digital Elevation Model (DEM) of the area and a tidal surface model that represents spatial tidal variability. The tidal model is created using the NOAA National Geodetic Survey's VDATUM datum transformation software in conjunction with spatial interpolation/extrapolation methods and represents the MHHW tidal datum in orthometric values (North American Vertical Datum of 1988).
The model used to produce these data does not account for erosion, subsidence, or any future changes in an area's hydrodynamics. It is simply a method to derive data in order to visualize the potential scale, not exact location, of inundation from sea level rise.
See NOAA's detailed methodology for producing these data.
For a detailed description of the mapping confidence level data and its computation, please see the Mapping Inundation Uncertainty document.
MassGIS downloaded all the data from https://coast.noaa.gov/slrdata/ and combined the separate inundation polygon feature classes into one feature class that contains no overlap. The processing included Dice (for faster drawing speed), Dissolve, Union, and field calculations. This combined layer, as well as the original mapping confidence rasters, were projected to the NAD 1983 Mass. State Plane Mainland Meters coordinate system.
The Sea Level Inundation polygon feature class contains the field SLR_CODE_NUM (Sea Level Rise Code), which stores a short integer (0-10) that represents the amount in feet of projected sea level rise required for that area to become inundated.
Each pixel in the Mapping Confidence raster datasets are coded as follows:
0 = Areas mapped as dry (no inundation) with a high confidence or low uncertainty
1 = Areas mapped as dry or wet with a low confidence or high uncertainty
2 = Areas mapped as wet (inundation) with a high confidence or low uncertainty
NOAA maintains the original data. MassGIS will download and process updates as necessary.
Last updated on 4/23/2021