Cape Cod Sea Level Rise
Produced by the Cape Cod Commission
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Current High Tide

At present Cape Cod is 383 square miles with 116,031 acres of Priority Habitat. There are 728 Critical Facilities and 3,121 miles of roadway. Annual sales equal $19.7 billion and 127,412 people are employed in 14,658 businesses.

Low-lying Areas
Disconnected Roads
Critical Facilities (Filter Types)
Unaffected
Affected
SLOSH Hurricane Categories
Category 1
Category 2
Category 3
Category 4
FEMA FIRM Floodzones
Special Flood Hazard Areas
Coastal High Hazard Areas
More Information

Introduction

This web mapping application is intended as a visualization tool to illustrate the vulnerability to climate change and hazards related to significant metrological events. Shown are potential Sea Level Rise increments, Sea, Lake and Overland Surges from Hurricanes (SLOSH) as well as the Federal Emergency Management Agency (FEMA) Flood Insurance Rate Map (FIRM). Also shown are the town identified critical facilities for the entire Cape as well as roadways that might be disconnected from the network due to flooding caused by sea level rise. By clicking on the map, demographic information is provided in a popup. Statistics are provided that begin to quantify the impact of sea level rise on Cape Cod in respect to; total acres lost, priority habitat lost, number of critical facilities impacted, roadways submerged and disconnected from the network, as well as lost business and jobs.

The Sea Level Rise data was derived from classified Digital Elevation Model (DEM) data collected through Light Detection and Ranging (LiDAR) in 2011 by the USGS. The elevation data is accurate to 18 cm at a 95% confidence level with a 1 meter resolution. This elevation data was adjusted to Mean Higher High Water (MHHW) using the NOAA VDatum Software. The Sea Level Rise is shown as a simple representation of a change in elevation, commonly referred to as a “Bathtub” model. No account has been made for the effects of velocity and resulting erosion caused by wave action.

The SLOSH model is a computerized numerical model developed by the National Weather Service (NWS) to estimate storm surge heights resulting from historical, hypothetical, or predicted hurricanes by taking into account the atmospheric pressure, size, forward speed, and track data. These parameters are used to create a model of the wind field which drives the storm surge. The SLOSH model consists of a set of physics equations which are applied to a specific locale's shoreline, incorporating the unique bay and river configurations, water depths, bridges, roads, levees and other physical features. Further information can be gathered from the National Weather Service

A FIRM is an official map of a community that displays the floodplains, more explicitly Special Flood Hazard Areas (SFHA) and Coastal High Hazard Areas (CHHA), as delineated by FEMA. Both areas are subject to inundation by 1-percent-annual chance flood. Structures located within the areas have a 26-percent chance of flooding during the life of a standard 30-year mortgage. The SFHA is the area where the National Flood Insurance Program's (NFIP's) floodplain management regulations must be enforced and the area where the mandatory purchase of flood insurance applies. The CHHA is an area of special flood hazard extending from offshore to the inland limit of a primary frontal dune along an open coast and any other area subject to high velocity wave action from storms or seismic sources. The coastal high hazard area is identified as Zone V on Flood Insurance Rate Maps (FIRMs). Special floodplain management requirements apply in V Zones including the requirement that all buildings be elevated on piles or columns.

Even though the Sea Level Rise, SLOSH and FEMA FIRM datasets can be viewed simultaneously, they should not be considered directly related (as shown). Certain inferences can be made as to the vulnerability of geographic regions based on its susceptibility to flooding from each, or all, of the hazards shown in this application.

The critical facilities shown were originally designated by each town during the development of the Risk and Vulnerability Assessment Maps (RVAM). There is currently a process underway at the Cape Cod Commission to review this designation and create a more regional classification of critical facilities.

The business data used was sourced from ESRI Business Analyst and is current to September 2012. This dataset is a point feature class created by geocoding business addresses using the Navteq Address Points database.

ESRI Network Analyst was used to determine which roads are disconnected from the network at each increment of Sea Level Rise. The network was created using the 2013 Navteq road dataset and service areas generated from a facility located on a high elevation. Thus, any roadway that was seperated from this facility by a barrier caused by flooding was identified by the software and would be considered disconnected.

The Social Vulnerability dataset was sourced from ArcGIS Online. This dataset shows a simple summary of the social vulnerability of populations in the United States. Using Census 2010 information, the map answers the question “Where are the areas of relatively greater potential impact from disaster events within the U.S.?” from the perspective of social vulnerability to hazards. In other words, all areas of the U.S. are assessed relative to each other. Local and regional assessments of social vulnerability should apply the same model to their multi-county or multi-state region. More information can be obtained from the metadata.

A video has been created to help users navigate and use the application, as well as a brief outline of the technology and methodology used to create it.

Sea Level Rise on Cape Cod

Sea levels are rising globally due to the melting of glaciers and ice sheets and the thermal expansion of ocean water, both of which are driven by overall climate warming. In Massachusetts, these factors are further amplified by the local subsidence of land (Massachusetts Executive Office of Energy and Environmental Affairs, 2011). Relative sea-level rise in Massachusetts from 1921 to 2006 was 2.6 millimeters annually (0.10 inches/year), an increase of approximately 26 centimeters or 10.2 inches per century. The map below illustrates regional trends in sea level, with arrows representing the direction and magnitude of change. Click on the map to open the source from NOAA.

NOAA Sea Level Rise NOAA Sea Level Rise

Projections of future global sea-level rise by 2100 range widely depending on a number of factors, including emission scenarios, temperature scenarios (influencing thermal expansion), and rates of glacial melting and discharge. The table below (SLR-1) contains a summary of possibly ranges.

SLR Projection Table

The impacts of projected increases in the rate of sea-level rise on Cape Cod are multi-fold and will pose significant threats to coastal communities. Sea-level rise will increase the height of storm surges and associated coastal flooding frequencies, worsening shoreline erosion and causing permanent inundation of low-lying areas. The frequency of today’s 100- year flood events will significantly increase, putting the extensive development and infrastructure, both public and private, along much of the Cape’s shore at risk (Kirshen et al., 2008).

Increased sea level will also threaten barrier beaches and dunes, weakening the Cape’s natural resilience during storm events. Salt marshes will be put at risk as they may be unable to keep pace with rising water levels and/or migrate inland along developed shorelines due to the presence of coastal structures. The range of tides in coastal ponds and estuaries may be altered with changes in inlet geometry, influencing salinities and the distribution and abundance of coastal marshes. Saltwater will also intrude on freshwater aquifers as sea levels rise, potentially affecting drinking water supplies and gradually converting freshwater wetlands to brackish and salt marshes. The myriad impacts of sea-level rise are discussed in greater detail in the following sections.

SEA-LEVEL RISE IMPACTS TO COASTAL EROSION AND FLOODING

Rising sea levels are an important driver of beach erosion, with long-term horizontal shoreline retreat rates averaging many times that of vertical sea-level rise. The long-term rate of shoreline change for all Cape Cod communities is -0.68 ft./yr., slightly higher than the statewide average, and varies significantly by coastal region (Cape Cod Commission Regional Hazard Risk Map). Back-barrier regions (i.e., coastal lagoons, salt ponds) around the world may respond to sea-level rise quite differently due to variations in sediment supply and saltmarsh accretion rates (see Marine Biological Laboratory Library web site ). Changes in inlet geometry, flow dynamics, and net sand transport directions can be expected if sea-level rise alters the shoaling character of tidal wave propagation into the backbarrier basin. These alterations will produce changes in tidal range, tidal prism, ebb and flood durations, and strength of the tidal currents (see Marine Biological Laboratory Library web site ). The loss of marshlands will increase tidal exchange between the ocean and back-barrier and ultimately change the direction and force of water flows in tidal inlets.

Case studies in the United States suggest that some areas flooded once or twice a century, today would be flooded every decade if sea level rises one meter. A higher water table (driven by sea-level rise) reduces the ability of the soil to absorb runoff, increasing the likelihood of flooding (see New York State Sea-level Rise Task Force Report to the Legislature , 2010).

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