Stephen Young, Department of Geography Center for Economic Development and Sustainability Salem State College

Many people want to know: How high will the ocean be in 2020 or 2050? And…. Where will flooding occur in my town?

I can’t tell you exactly, but……

It is possible to determine a potential range of future sea-level rise and to map out the vulnerable areas of your town.

Today I want to leave you with an understanding of two basic issues:

1) How sea-level is rising and the scientific uncertainties around how fast it is rising.

2) How we go about mapping the vulnerability of our coastal environment.

The good news first -

The Northeast is one of the least vulnerable coastal areas of the US. However, we are still vulnerable and need to prepare.

Is the sea rising? And if so how fast?

“Global sea level is rising, and there is evidence that the rate is accelerating.”

Sea-level rise is caused by three factors: 1) Thermal Expansion of the ocean as the waters warm. 2) Addition of Water by the melting of land-based ice sheets, ice caps, and glaciers. 3) Relative sea-level rise due to the changing elevation of the adjacent land (subsidence & rebound).

How fast is it rising? East Coast US, 20 th Century: 3 to 4 mm per year (1.2 to 1.5 inches per decade). In the 20 th Century Massachusetts saw about a 10 to 11 inch increase in sea-level.

Concerning the melting of global ice – it has rapidly increased and some scientists now estimate that added water is now the main cause of sea-level rise (which has been thermal expansion).

Arctic Climate Research – University of Illinios

Journal: Skeptical Science

Ice mass loss in Greenland as observed by satellite Grace in cubic kilometers per year. NASA/JPL/University of Colorado

Mean size measured on 30 glaciers in 9 mountain ranges. From: World Glacier Monitoring Service

Fresh Water - where it is

Second, how we map the vulnerability of our coastal environment.

To understand how we map the vulnerability of coasts, we need to understand the potential harm caused by rising sea levels.

These include: 1) Inundation from a rising sea-level. 2) Flooding from storm activity, especially storm surges on top of a higher sea level. 3) Inland flooding from storms partly caused by altered drainage patterns due to the rising sea-level. 4) New erosion patterns due to changing water flow and sea level. 5) Inability of natural ecosystems to change with rising sea levels.

Today rising sea levels are eroding beaches, submerging low-lying areas, converting wetlands to open water, increasing storm flood activity and increasing the salinity of estuaries and freshwater aquifers. Some natural areas are able to adjust to the changes by shifting upward and landward with the rising waters, but areas confined by development are more vulnerable and are not able to adjust.

Once we understand the potential consequences in our town we can begin to develop a mapping strategy.

1) Determine a range of future sea-level rises. 2) Get accurate geo-referenced elevation and coastal image data as well as infrastructure and social data. 3) Characterize the coast’s geomorphology. 4) Run various simulations based on different sea-level rises and different storm activity. 5) Produce static maps of potential damage.

1) Determine a range of future sea-level rises. Intergovernmental Panel on Climate Change (IPCC), 2007, project that in the 21 st century global sea-level will rise between 7 and 23 inches. Right now, March 2009 there is a major climate change conference in Copenhagen and most scientists are now estimating a rise of 1 meter (39 inches) or more – about double the high end of the IPCC, 2007 report.

2) Get accurate geo-referenced elevation and coastal image data as well as infrastructure and social data. Elevation data is the most important data to determine the influence of sea-level rise, and it is critical to understand the accuracy of the data.

There are existing national standards for quantifying and reporting elevation data accuracy. For most current elevation data sets, the accuracy error is greater than the high-end of potential sea-level rise (1 meter).

High-quality LIDAR elevation data should be the base data for sea-level rise maps. These data sets also need to be field checked. High-resolution coastal LIDAR data is now becoming available at NOAA (

3) Characterize the coast’s geomorphology. This needs to be done through field work. In some areas the extent of inundation is controlled largely by the slope of the land with gentle slopes being the most vulnerable. Also barrier island migration and wetland accretion and shoreline erosion will alter inundation.

4) Run various simulations based on different sea-level rises and different storm activity. This can be done with various GIS software.

5) Produce static maps of potential damage. Again this can be done with various GIS software.

Despite the dearth of quality elevation data, some crude modeling can be done now to provide some broad patterns of potential change. For example MASS GIS now has some Digital Elevation Model (DEM) data which can be used for modeling, but with the understanding of its internal errors.

“This map is based on modeled elevations, not actual surveys or the precise data necessary to estimate elevations at specific locations.” J.G.Titus and C.Richman, 2000, “Maps of Lands Vulnerable to Sea Level Rise: Modeled Elevations Along the U.S. Atlantic and Gulf Coasts.” Climate Research