This tool enables users to simulate the impact of hurricanes and nor’easters, using the same models that produce Flood Insurance Rate Maps.
Purpose: Evaluate exposure to natural hazards like strong winds, waves and surge (based on topography and bathymetry at a given location) for specific user-defined scenarios.
Use Cases: (1) Emergency management during landfalling storms; (2) planning activities such as risk assessments or development of Floodplain Management Plans.
Challenge: Static visualizations of projected flood hazards, such as digital flood insurance rate maps (DFIRMs), do not allow municipalities to evaluate specific scenarios for planning and situational awareness applications; models used to create static visualizations like DFIRMs or other flood hazard maps, are themselves too complex and computationally demanding to be run by non-experts on standard desktop computers.
Response: NJcoast has developed a pair of computational models — one for nor’easters and one for hurricanes — using a technique called surrogate modeling (see inset panel). Surrogate models allow any arbitrary storm to be simulated once users select the landfall location and storm intensity (Category 1, 2, etc.) values. In minutes, these models produce a geospatial layer visualizing the expected storm surge and the extent of waves driving the water over land. The tool even allows users to project “worst case scenarios” given uncertainties in the track prior to landfall. A highly efficient wind field model also generates a second geospatial layer mapping site-specific wind speeds anticipated during the storm.
Enhancements: The surrogate model is based upon the data generated by the Army Corps of Engineers North Atlantic Coast Comprehensive Study (NACCS). This database is being enhanced with wave run-up simulations at specific locations (transects) along the New Jersey coast. This captures the interaction of the waves with the current level of coastal protection and can allow users to explore the impact of degradation or loss of this protection. The wave-run up simulations (for current levels of coastal protection) are being included for the Sandy-affected counties of Cape May, Atlantic, Middlesex, Monmouth, Essex, Hudson, Union and Ocean; additional simulations for degraded or compromised coastal protection will be available for the pilot communities of Keansburg and Berkeley. The wind model similarly evaluates land use/land cover patterns to simulate specific wind speeds based on topography for the entire state of New Jersey.
User Options: Using the NJcoast interface, users can choose a Nor’easter or hurricane simulation at a given coastal protection level (current, degraded, compromised) and also explore the impacts of elevated sea level and tides.
Active Storm Mode: During a landfalling storm, NJcoast will automatically execute the Storm Hazard Projection Tool with the properties of the latest storm track reported by the National Hurricane Center and have this result available on the user’s dashboard.
Get Started: To use the SHP Tool, you will need to request a user account.
A surrogate model is basically a highly sophisticated interpolation approach. The Army Corps of Engineers regularly conducts studies of US hurricane zones. Most relevant to New Jersey is their North Atlantic Coast Comprehensive Study (NACCS) during which the Corps ran over 1000 synthetic storm tracks and 100 historical storm tracks for hurricanes and nor’easters in this region. Their simulations used the ADCIRC model co-developed at Notre Dame to calculate the surge for each of 1100+ storm tracks, coupled with a second model called STWAVE that simulates the additional effects of waves offshore. The NACCS also considers the effects of nearly 100 random tide scenarios and a 1 m sea level rise. This results in a massive database of hurricane storm surge predictions all along the East Coast for each of these 1100+ storm tracks, under different tidal and sea level scenarios. That’s where the surrogate model comes along.
It turns out that storm tracks are easily described by a handful of common parameters, like landfall location and central pressure. These are used to calibrate a surrogate model against the Army Corps NACCS database. Once the surrogate model is tuned to the database, it can be used to simulate any arbitrary storm simply by inputting the desired values of these parameters, even if those parameters do not exactly match the properties of the 1100+ tracks in the original NACCS database. Validations against wave gauges in recent hurricanes like Sandy in New Jersey and Harvey in Texas have shown this approach to have outstanding accuracy.
Because of its efficiency, the surrogate model is even able to evaluate the uncertainty in the storm track. Since storms can shift considerably in the days and hours leading up to landfall, the surrogate model takes the user’s inputs and determines the different ways that track could deviate prior to landfall to show the user the uncertainty in the storm track and an estimate of worst-case storm surge scenario.