DNR Answers Questions about Sea Level Rise
In Response to IPCC Report

On Friday, February 2, 2007, the Intergovernmental Panel on Climate Change (IPCC) issued the Summary for Policymakers for their Fourth Assessment Report. People all over the world are now asking what the findings and projections detailed in the 21-page report mean for their respective locations.

In Maryland, the Department of Natural Resources has been working for more than a decade to better understand both climate change and sea level rise and how these phenomena will impact the State’s coastline. DNR today posted an in-focus page on its website to help citizens better comprehend the recent findings of the IPCC.

How do you measure sea level rise? Measurement of sea level at any particular location is relative. Relative sea level rise is the sum of global (eustatic) sea level change plus changes in vertical land movement at a particular location due to tectonic, neotectonic, and anthropogenic impacts. Scientists measure sea level rise by examining historic tide-gauge records in combination with measurements of vertical land movement.

Is sea level rising within Maryland waters? Yes. Historic tide-gauge records document that sea level is rising in Mid-Atlantic waters and the Chesapeake Bay at an average rate of 3 to 4 millimeters (mm) per year. There has been approximately one foot of sea level rise in the Chesapeake Bay over the past 100 years. This rate is nearly twice that of the global historic average, as reported in the IPCC report. Maryland is experiencing more of a rise in sea level than other parts of the world, due to naturally occurring regional land subsidence. Land is currently subsiding in the Chesapeake Bay region at a rate of approximately 1.3 mm/year.

How much will sea level rise? The IPCC report projects that global sea levels will rise between 7 and 23 inches by the year 2099. For Maryland waters, regional land subsidence must be factored into the equation in order to estimate relative sea level rise. This means that the State could experience an additional 5 or more inches of sea level rise, over and above what is being experienced globally, in the next 100 years. At the very least, a continuation of the current sea level rise trend (3 to 4 mm/year) or one foot over the next century is expected to occur in the Mid-Atlantic region. This is the most conservative and low-end estimate. The IPCC report documents that the global rate of sea level rise has started to accelerate. This means that Maryland could see as much as 2 or 3 feet of rise by 2099.

How vulnerable is Maryland’s coastline to sea level rise? Due to its geography and geology, the Chesapeake Bay region is ranked the third most vulnerable, behind Louisiana and Southern Florida. In fact, sea level rise impacts are already being detected all along Maryland’s coast. The primary impacts of sea level rise include intensified coastal flood events, increased shore erosion, inundation of wetlands and low-lying lands, and salt-water intrusion into groundwater. Maryland’s varied coastline is highly susceptible to all such impacts.

Shore Erosion: Erosion is a significant problem currently facing Maryland’s diverse coastal environment. Approximately 31% of Maryland’s coastline is currently experiencing some degree of erosion. Sea level rise is a causal force which influences the on-going coastal processes that drive erosion, in turn making coastal areas ever more vulnerable to both chronic erosion and episodic storm events (Nor’easters, tropical storms, hurricanes). Maryland is currently losing approximately 580 acres of land per year to shore erosion.

Coastal Flooding: As demonstrated by Tropical Storm Isabel in 2003, Maryland’s coastline is extremely vulnerable to coastal flood events. Sea level rise increases the height of storm waves, enabling them to extend further inland. In low-lying coastal areas, a 1-foot rise in sea level translates into a 1-foot rise in flood level, intensifying the impact of coastal flood waters and storm surge. The risk of damage to properties and infrastructure all along the Bay and Atlantic Coast will be heightened as sea level continues to rise.

Inundation: For many coastal areas, slope is the primary variable controlling the magnitude and range of sea level rise impact over time. In areas such as Maryland’s Eastern Shore where elevation change may only be as much as 1 foot per mile, gradual submergence of a large geographic area, including large expanses of tidal wetlands, is quite likely over time. Land inundation due to sea level rise is already occurring along low-lying coastal areas in Dorchester and Somerset Counties.

What is the Department of Natural Resources doing about sea level rise? The Department of Natural Resources Coastal Program has directed substantial efforts towards analyzing and addressing the impacts of sea level rise over the past 10 years. In addition to supporting collaborative research into the physical impact of sea level rise, the Program has worked hard to identify ways the State and its coastal communities can mitigate for associated impacts. Recent accomplishments include:

• DNR published a Sea Level Rise Response Strategy for the State of Maryland (http://www.dnr.state.md.us/bay/czm/sea_level_rise.html) in 2000. The Strategy set forth both short and long term objectives, along with key activities, to address the physical impacts of sea level rise. DNR is using the Strategy to guide its current sea level rise planning efforts.
   

• DNR worked with State and local partners to acquire high resolution topographic data for the majority of the State’s coastal counties. This data can be used to develop sea level rise inundation models that demonstrate both the impact of gradual sea level rise inundation over time, as well as impacts associated with increased storm surge from episodic flood events. Sea level rise modeling has been completed for Worcester County. (http://www.dnr.state.md.us/bay/czm/wcslrreport.html), Dorchester County, and pilot areas within Anne Arundel and St. Mary’s Counties.
   

• DNR recently launched an interactive web portal: Shorelines Online (http://shorelines.dnr.state.md.us/), which centralizes information and data on coastal hazards management and sea level rise in Maryland.

The Department of Natural Resources is continuing to work with State and local partners to further understand and plan for sea level rise. The release of the IPCC report has drawn international and national attention to the need to plan for sea level rise. Maryland is ahead of many other coastal states when it comes to planning; and, it should remain so, given the region’s extreme vulnerability to associated impacts.