Hurricane Harvey, Hurricane Irma, Hurricane Jose, Hurricane Maria. In just the past month, the Caribbean Islands and the United States have seen an unprecedented number of Category 4 and 5 hurricanes. Islands, including Martha’s Vineyard, are particularly vulnerable to the effects of these violent storms. What effects will climate change have on the Island, and how should the Vineyard plan on mitigating this threat?
Since 1895, average temperatures has risen by about 2° Fahrenheit, said Jeremy Houser, communications director and ecologist at the Vineyard Conservation Society (VCS). This temperature rise is due to number of natural and unnatural events, specifically increased usage of CO2 and agricultural practices. Due to this temperature rise, throughout the world we have seen sea level rise, changes in weather patterns, extinction of animals, drought, and food shortages.
Sea-level rise, one of the main consequences of climate change, is caused by the increasing temperature, which leads to the melting of land ice, including the mountain glaciers and ice sheets of Greenland and Antarctica. The sea level has been rising at a rate of about 2.5 to 2.8 mm (0.09 to 0.11 inches) each year, equivalent to about the size of a flea. While that doesn’t seem significant, this has resulted in a foot of sea-level rise in the past 100 years. Over the next century, this rate is expected to increase substantially, said Rob Thieler, director of the U.S. Geological Survey’s Woods Hole Coastal and Marine Science Center. “Most models indicate a three- to four-foot sea-level rise in the next 100 years, and to put that in perspective, we haven’t experienced a sea-level rise that drastic in about 10,000 years,” said Mr. Thieler.
The effects of sea-level rise go beyond a simple increase in ocean heights. With a three- to four-foot sea-level rise, the Vineyard could see a completely changed coastal landscape due to coastal erosion and flooding.
The coast erodes due to three factors: the type and amount of sediment in the water, the amount of wave energy present, and the level of the sea, said Mr. Thieler. “Think of yourself in a sandbox with a bulldozer, and the bulldozer is the waves,” he said. While the rate of coastal erosion has remained steady over the past years, it has been moving mainly landward, not seaward. As such, the entire coastline is expected to change. The bathtub model, which measures sea-level rise evenly in all locations, is not accurate for most of the Vineyard, if not all of it, said Mr. Thieler. Due to the differences in sediment and coastline structure, Martha’s Vineyard will see the sea rise by varying amounts in different locations. This makes the exact effect of sea-level rise on the Island’s coast hard to predict. Yet a look at historical shoreline data can provide an idea of what to expect. “The barrier spit across Katama Bay, around 1897, used to be about 1,500 feet farther into the ocean than it is today,” said Mr. Thieler.
As experience with heavy rainstorms shows every time they occur, flooding will pose a major problem. “A little sea-level rise translates to a really big change in flood frequency,” said Mr. Houser. With a sea-level rise of 1.5 feet, the possibility of having a flood by 2050 that is five feet above the mean high tide mark, which would result in about $1.1 billion of damage, is 37 percent, said Mr. Houser. With a five-foot rise in sea level, the chance of that flood happening by 2050 increases to 95 percent. As stated before, the Vineyard is currently looking at a sea-level rise of three to four feet in the next century.
As the atmosphere gets warmer, the frequency of powerful storms, such as Category 5 hurricanes, increases. This will yield more dangerous storm surges and flooding, the most lethal parts of hurricanes. “Many of the ways we’ve developed the coast have made us increasingly vulnerable to changes in storm climate,” said Mr. Thieler. During a storm surge, the water level rises due to a change in atmospheric pressure and wind that accompanies a hurricane. The amount of storm surge depends on the size of the hurricane, and therefore is hard to predict. But, it is clear that storm surge, coupled with sea level, could pose significant problems for Martha’s Vineyard, said Mr Houser. “It’s a question of where the sea is.”
So, where do Islanders get involved? “People are a part of the climate change response. We’re going to chose to do things or not to do things,” said Mr. Thieler. In regards to coastal erosion, Islanders can either build up seawalls to protect themselves, or retreat. “Our position at VCS is that in the face of climate change, we need to defend the natural state of our beaches,” said Mr. Houser. If the beaches naturally move and change, the beach will always be there, just in a different location. If attempts are made to thwart the natural movement of sand, there is a risk of losing beaches, said Mr. Houser. “Coastal wetlands are our greatest protection from climate change, and greatly threatened by it.” These areas create a barrier between houses and the beach, and can absorb a lot of force from the ocean. In the face of severe flooding, these areas will be critical.
To deal with flooding and storm surge, in 2015 the Martha’s Vineyard Commission created the Dukes County Multi-Jurisdiction Hazard Mitigation Plan. This plan has mapped what expected sea-level rise will be in each town, and developed a plan for each town on how to combat climate change. With this plan in place, each town is eligible to receive 75 percent funding for action projects from the U.S. government, said Jo-Ann Taylor, project manager and principal author of the report. “We have roads, ferries, barges, and bridges that are all vulnerable to sea-level rise,” said Ms. Taylor. The plan calls for structural retrofitting, larger stormwater facilities, and increased fire protection in the State Forest. “With climate change, we will begin to experience short-term drought with heavy rainstorms,” said Ms. Taylor. “While we will have the same amount of rainfall, the distribution will be different, and our stormwater facilities are not equipped to handle that … who hasn’t seen Dock Street underwater?”
This plan will be updated, and is set to be approved by the towns by 2020. The update will account for a more heavy rainfall and the effects of storm surge and sea-level rise combined, Ms. Taylor said.