Coastal Risk Mapping in Salem Sound
Geoscience Consultants generated time-based inundation risk map outputs of present and future (up to 2100) inundation from SLR at mean higher high water, shallow coastal flooding, category 1 hurricanes, and still-water annual storm surge in the Salem Sound Coastwatch communities of Northeast Massachusetts. The primary objective was to provide easily understandable and self-contained information for decision makers and citizens that incorporates a probabilistic handling of the uncertainties involved in documenting future coastal hazards. This work built on existing models and concepts by providing a unique and intuitive approach to mapping coastal hazard risks.
The need addressed in this project comes largely from NOAA and is clearly stated on the first page of the US National Climate Assessment report on Global Sea Level Rise Scenarios (NOAA, 2012).
“At present, coastal managers are left to identify global SLR estimates through their own interpretation of the scientific literature or the advice of experts on an ad-hoc basis.”
The lack of risk-based information for the US is a problem, and has been voiced repeatedly in the past five years. People, municipalities, states, and the federal government have a difficult time agreeing on a single (deterministic) SLR value to help define risk (NOAA, 2012). Uncertainty in SLR projections is a large factor, among other physical processes, in determining coastal hazard risks. The outputs address these issues by including the fundamental aspect of time - it’s relation to uncertainty in future Sea Level Chance (SLC) scenarios , data errors, and model ensembles. For example, the uncertainty in the 2020 SLC risk assessment is extremely small as compared to 2075; the developed risk maps honor that fundamental aspect of time.
The evolution of coastal hazard mapping has been advanced significantly in the US by both NOAA and Climate Central. Further advance in the state of the art is, however, needed as more risk is felt along the coastal regions of the US. This new risk mapping technique provides these important improvements to the existing techniques:
a. Time is a component and is risk-based in nature
b. Results are based on probabilities and allows different parties to select levels that are consistent with their own ability to handle risk, e.g., hospitals cannot tolerate the same level of risk as a private residence.
c. Maps provide a Risk % for all mapped areas – even those that are not within the present limits of inundation.
d. Maps incorporate additional risk data such as historic water levels and SLOSH data with tide levels.
e. Mapping outputs can be combined with other ancillary data to provide regional summaries or focused results.
