Imagine a hurricane acting as a plow, with water piling up at the front of the storm and the highest water levels accumulating at its right-front side as it spins counter-clockwise. When the hurricane makes landfall, the waves cause mass devastation since each cubic yard of seawater weighs almost a ton.
This is what storm surge looks like and it occurs when powerful winds, like those from cyclonic storms, push water towards the shore, according to the 2018 Storm Surge Report from CoreLogic.
While last year’s hurricanes hit parts of the US with a ton of force, causing major losses for insurers and their clients, damage related to the phenomenon of storm surge during these disasters was less significant than you’d expect.
“Neither [Harvey nor Maria] is going to be remembered specifically for storm surge,” said Thomas Jeffery, principal of the science and analytics team at CoreLogic. “Harvey had tremendous, record-setting flooding, but most of the Harvey flooding in Texas was related to precipitation.”
Irma stands out because there was some storm surge damage in the Florida Keys, though a lack of concentrated high-density development in the affected area meant the loss wasn’t as bad as if Tampa or Miami were hit, which begs the question: what makes a region more prone to losses from storm surge?
The size of the population living along the most at-risk coastal areas has an obvious bearing on the level of destruction resulting from a surge.
“There are areas along the coastline – the Gulf coast and the Atlantic coast – where you don’t have a lot of dense population and if the storm comes ashore there, you’re just not going to experience the same type of loss that even a small storm would incur if it were to come ashore in or near a large metropolitan area,” explained Jeffery.
The terrain also plays an important role in the reach of a storm surge, which can travel up to a mile or more inland. A lower elevation near the coast means there’s a good chance homes or businesses in that area will experience more damage.
“The higher you are in elevation, or the further inland you are, the more remote you are from the potential threat,” said Jeffery. “Everyone associates storm surge flooding with that first row of homes right along the coastal area, but it definitely is not limited to those properties. That’s certainly a misconception because water can flow further inland than you would often expect, especially in low areas. It’s strongly correlated with elevation, so if you have a low area that extends far inland, like you would in a Galveston or a Miami area, you would see that water flow further inland.”
Another factor that people tend not to consider is the placement of structures near other bodies of water, not just the ocean.
“If you have a stream or a river or even a canal, it offers the ocean water a conduit to move inland and in those cases, you have storm surge that’s going to push up the river,” said Jeffery. “It actually can push quite far inland, farther than you would normally think, and then homes that are built along those waterways are at risk if they’re low enough in elevation.”
The weather forecast in the 2018 Storm Surge Report points to an average year for both the number of tropical storms and hurricanes, with 12 to 14 total named storms and six to seven hurricanes, though the unpredictability of where they’ll come onshore makes all the difference for determining how much damage will occur. Even a weak storm can lead to devastating storm surges, depending on the development in the region.
“The expectation is that we’re going to see less activity this year than last, but the problem that you have to be cautious about is that you can have a year with just a few storms, but depending on where they make landfall, you can have a tremendous amount of catastrophic damage,” said Jeffery. “And they don’t have to be strong storms to cause a lot of damage.”