PAST: Rising Sea Levels, Hurricanes, and Floods in Barnstable County

3/28/2020

Changes in sea level in Woods Hole, Massachusetts from 1930 through today. Source: NOAA Tides and Currents.

Climate change and the local environment:

As atmospheric temperatures around the world soar, oceanic water temperatures are increasing too, and glaciers and ice sheets are melting. Because water molecules in warmer water exhibit greater molecular movement, water expands in volume as it heats up. Furthermore, melting polar ice adds to the amount of water not in ice sheets, again causing a rise in sea levels globally.

Nonetheless, it is important to recognize that regional variations in atmospheric and oceanic circulation patterns, in addition to other factors, also influence the extent of sea level rise. As global sea levels continue to rise, exposed coastal communities must be prepared for an increased risk of flooding. Barnstable County, located on Cape Cod in Massachusetts, has already experienced a sea level increase of 11 inches since 1922, almost 2.85mm annually. Its vulnerable coastal position, located on 550 miles (890 km) of shoreline, contributes to the risk of flooding in the County in the face of sea level rise.

Average annual precipitation in Barnstable County from 1895 to the present. Source: NOAA Climate at a Glance.

Barnstable County has also seen an upward trend in annual precipitation levels. As the atmosphere warms, the rate of evaporation increases. Quicker rates of evaporation pulls more water into the atmosphere which is then accessible for precipitation. Thus, the overall trend of atmospheric warming contributes to the rise in both frequency and intensity of precipitation events. Despite the annual variation in precipitation levels, the general progression seen over the past century in the graph above shows increasingly wetter conditions for Barnstable County.

Hurricanes are also becoming more powerful as a consequence of warming global temperatures. Because hurricanes form over warm ocean waters, the increase in oceanic temperatures fuel hurricanes with more energy to activate higher peak winds and greater rainfall. Sea level rise also worsens the damages of hurricanes, as higher coastal inundation levels can increase the risk of storm-surge flooding. Although climate change does not necessarily impact the frequencies of hurricanes, it increases the severity of storms that have the potential to reach the coast of Cape Cod and cause tremendous damage.

Coastal flood days in Barnstable County, categorized as floods driven by climate-linked sea level rise or those that would have occurred anyway. Source: Surging Seas Risk Finder

The increased levels of precipitation, rising sea levels, and more powerful hurricanes have elevated the number of coastal flooding days in Barnstable County. These factors have not only made floods become more frequent, but have also made them more severe. The graph above shows the growing number of coastal flood days that can be linked to climate-driven sea level rise. The County has already experienced severe coastal flooding, and likely will suffer in the future as temperatures and sea levels continue to rise.

How we know:

This information relies on data from easily accessible online tools including the National Oceanic and Atmospheric Administration (NOAA) Tides and Currents tool, the NOAA Climate at a Glance resource, and Climate Central’s Surging Seas: Risk Finder projections. It also draws on conclusions from a NOAA study connecting hurricane severity to global warming.

The NOAA Tides and Currents resource collects data from over 100 water level stations in order to reconstruct sea level trends at the local level. The NOAA Climate at a Glance tool generates graphs using data gathered from weather stations to show trends in temperature, precipitation, and drought on global, regional, and local scales. Climate Central’s Surging Seas projections display sea level rise and flood risks for coastal locations.

Human consequences:

Barnstable County acts as one of the biggest barrier islands in the world, shielding Massachusetts from the full weight of storms. Because of its location, the County’s shoreline is vulnerable to coastal flooding in the face of hurricanes. Even during small rain events, the Barnstable County drainage system is overwhelmed, resulting in the flooding of state roadways and personal properties. The heavy rainfall associated with severe hurricanes has caused especially severe flooding and significant property damage.

Hurricanes throughout the 20th century have been tremendously destructive in Barnstable. The Great New England Hurricane of 1938 struck the Cape at a high tide, causing a storm surge of up to 15 feet. The devastating effects of the storm were felt throughout Barnstable County’s southern coast and into many of the inlets and bays. Parts of the County were flooded with up to 8 feet of water and struck with winds that reached over 120 mph, causing damage to houses, trees, and crops. With rainfall totaling over 17 inches, thousands of homes, businesses, and fishing fleets were destroyed or damaged from severe flooding.

Barnstable County was again hit with a devastating hurricane in August of 1991, with Hurricane Bob damaging Buzzards Bay most significantly. Most of the County was under 5 to 10 feet of water, with wind gusts reaching over 120 mph. Many Massachusetts residents were left without power, and beaches suffered greatly from eroding coastlines. This hurricane forced a full evacuation in the height of the tourist season, shutting down the Cape for the rest of the summer and threatening the economic livelihood of many occupants. Hurricane Bob proved to be costly, with over $69 million in damages to public property, as well as $10 million of agricultural damages to local peach and apple orchards.

The intensity of hurricanes and the risk of coastal flooding in Cape Cod has only increased throughout the past century. As temperatures warm and sea levels rise, these can only be expected to become more common and devastating in the future. While low cost flood insurance has been provided to the community, Barnstable County must decipher the best way to build up resilience in the face of the rising threat of climate change in order to keep its beloved coastal communities intact.