These data were created as part of the National Oceanic and Atmospheric Administration Coastal Services Center’s efforts to create an online mapping viewer depicting potential sea level rise and its associated impacts on the nation’s coastal areas. The purpose of the mapping viewer is to provide coastal managers and scientists with a preliminary look at sea level rise (slr) and coastal flooding impacts. The viewer is a screening-level tool that uses nationally consistent data sets and analyses. Data and maps provided can be used at several scales to help gauge trends and prioritize actions for different scenarios. The Sea Level Rise and Coastal Flooding Impacts Viewer may be accessed at: http://www.csc.noaa.gov/slr.
These data depict the potential inundation extent of coastal areas resulting from National Weather Service issued Coastal Flood Advisories. The Coastal Flood Advisory areas are based on individual Weather Forecast Office (WFO) guidance thresholds at monitored tide stations and are referenced to the MLLW tidal datum. The process used to produce the data can be described as a modified bathtub approach that attempts to account for both local/regional tidal variability. The process uses either two or three source datasets depending on geographic location to derive the final inundation rasters: the Digital Elevation Model (DEM) of the area, a tidal surface model that represents spatial tidal variability, and an interpolated threshold surface if there is significant difference between flooding thresholds between varying geographic areas (Ex: Chesapeake Bay area). The tidal model is created using the NOAA National Geodetic Survey’s VDATUM datum transformation software (http://vdatum.noaa.gov) in conjunction with spatial interpolation/extrapolation methods and represents the MLLW tidal datum in orthometric values (North American Vertical Datum of 1988).The interpolated threshold surface is created using the flooding threshold values found at select NOAA tide gages used by the NWS to define flooding events.
The methods 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 and extent, not exact location, of inundation from NWS issued Coastal Flood Advisories.
These data depict the mapping confidence of the associated Sea Level Rise inundation data, for the sea level rise amount specified. 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.
Areas mapped as dry (no inundation) with a high confidence or low uncertainty are coded as 0.Areas mapped as dry or wet with a low confidence or high uncertainty are coded as 1.Areas mapped as wet (inundation) with a high confidence or low uncertainty are coded as 2.
The NOAA Coastal Services Center 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.
For a detailed description of the confidence level and its computation, please see the Mapping Inundation Uncertainty document available at: http://www.csc.noaa.gov/slr/viewer/assets/pdfs/Elevation_Mapping_Confidence_Methods.pdf
