Following are some sources for additional information on hazard risks your community may face. For details on how to use this information to help protect your community, see where to use additional information on coastal hazard risks.
For the latest (April, 2009) statistics on the likelihood of your county being struck by a hurricane, see The United States Landfalling Hurricaneor Web Project.
Shoreline Change History
New Hamsphire has not yet mapped its coastal change history. In general, there are a few areas that experience erosion from winter storms, however, many of the beaches are presenting aggrading. The US Geological Survey has recently released a study on shoreline change in New England and the Mid-Atlantic. Just south of the NH boundary, the Massachusetts Office of Coastal Zone Management has created detailed maps showing change of shoreline over time. Maps from Salisbury (Massachusetts) show that the beaches are changing; building up in some areas and being eroded in others. Mapping shoreline change history is a priority for the NH Coastal Program (NHCP) that should be accomplished in the near future.
Communities seeking more information on shoreline change and the risks that come with it can download a PDF of the Heinz Center’s Evaluation of Erosion Hazards.
Sea Level Rise Data and Projections
Precise long-term tidal measurements show that sea levels are rising. Rapid melting of glaciers and polar ice, along with increasing seawater temperatures are expected to exponentially increase the rate of sea level rise over the next century. Consequently, the effects of future, higher, sea levels should be considered when making siting decisions. For more information on current predictions for sea level rise, see the following:
- To date, the most detailed analysis of sea level rise for New Hampshire was a study completed by UNH in 2001. “A Preliminary Assessment of Tidal Flooding along the New Hampshire Coast: Past, Present and Future”(PDF, 1.6MB) by Larry Ward from Jackson Estuarine Laboratory details the potential inundation hazard presented by a 2 foot sea level rise.
- The U.S. Environmental Protection Agency is generally accepted as an authority on sea level rise trends. See their Sea Level Rise Reports and Coastal Zones and Sea Level Rise pages.
- The National Oceanographic and Atmospheric Administration’s Sea Levels Online graphs recent trends from Seavey Island, ME which is adjacent to Portsmouth, NH.
- The International Panel on Climate Change (IPCC) has extensive information on sea level rise available on their frequently updated web site.
- This Union of Concerned Scientists report (PDF, 540 KB) provides specific predictions on the effects of sea level rise in New Hampshire.
- Coastal communities can find general suggestions for means of adapting to rising sea levels and climate change in Preparing for Climate Change: A Guidebook for Local, Regional and State Governments.
- The Florida Institute of Technology has assembled a library of sea level and coastal climate adaptation.
- The U.S. Global Change Research Program’s Online Resource Library provides access to data and information on climate change research, adaptation/mitigation strategies and technologies, and global change-related educational resources.
Storm surge is water that is pushed toward the shore by winds. This advancing surge combines with normal tides to create the storm tide, which can increase the effective sea level 25 feet or more. Wind driven waves are added on top of the storm surge, creating tremendous potential for extensive storm damage.
- “A Preliminary Assessment of Tidal Flooding along the New Hampshire Coast: Past, Present and Future” (PDF, 1.6MB) by Larry Ward from Jackson Estuarine Laboratory details the potential inundation hazard presented by a 2 foot sea level rise. It also evaluates the current and potential impacts of storm surge for a variety of return intervals.
- The New England District of the U.S. Army Corps of Engineers has created hurricane surge inundation maps in PDF form for New England’s coastal communities (note: maps may be slow to download). GIS layers are also available.
With continuing sea level rise, more and more areas are at risk of flooding or being damaged by storm surge. Unfortunately, figuring out what areas are going to flood in the future is even trickier than determining which are most at risk now. NOAA has created a Coastal Inundation Toolkit with information coastal inundation is and how to address it. Also see their Mapping Coastal Inundation Primer (PDF, 1.4 MB).
For projections on approximate wind speeds in your community during different categories of hurricanes, see National Weather Service’s Hurricane Preparedness website.
In most communities, there are areas that flood that are not mapped as flood zones on the community’s Flood Insurance Rate Maps (FIRMs). Community decisions about land use in floodplains should be based on the actual floodplain, which should be determined from all available information, including the FIRM’s data, relevant parts of the Flood Insurance Study, and your community’s experiences. During and immediately after storm events, your community can record the true (as opposed to modeled) extent of a storm. This can be done in many ways—if aerial photographs are available, these can be used, as can physically recording the extent of floodwaters (high-water marks) during the peak hours of a storm event or soon after the storm when the evidence is still visible.
Other Sources of Hazard Information
- The NOAA Coastal Service Center’s Digital Coasts website, which couples data and tools together to help inform coastal decision makers. See their Digital Coasts in Action page for examples on how some communities (including several in the region) are using the site.
- The iCAT Damage Estimator is a web tool that shows storms from 1900 to the present with damage projections for how much damage each storm would cause if it were to hit today (read our post on the iCAT Damage Estimator).
Where to Use Additional Information on Coastal Hazard Risks
As your community’s understanding of local flood and erosion risks improves, so do your chances of successfully addressing them. For example, more detailed information on areas prone to flooding, erosion, or storm damage will allow your community to better plan for development in its master plan, more efficiently prepare for emergencies in its disaster response plan, and more effectively help educate its citizens as to the real risks they face. Following are some areas where your community can use its newly found hazard information.
- Regulations and Development Standards
- Emergency Services
- Education and Outreach
* Your community needs only 500 points to qualify for reduced flood insurance premiums through the Community Rating System (CRS). For more information (including how to apply for the CRS program), see our Community Rating System (CRS) primer.
Notes from the folks at CRS:
“Local governments preparing floodplain management plans or hazard mitigation plans should seek and utilize flood risk information from Federal, State and Regional agencies. For coastal communities this should include information on their shoreline change history, sea-level rise and storm surge. More credit is provided to local governments that research and use information on other risks such as high winds, subsidence and ground movement. In CRS that effort is credited under Activity 510 Floodplain Management Planning.”