How sea level rise contributes to billions in extra damage during hurricanes
Posted on 1 November 2022 by Guest Author
This is a re-post from Yale Climate Connections by Jeff Masters
When Hurricane Ian barreled into the coast of southwest Florida on Sept. 28, the mighty hurricane’s 150-mph winds drove a massive and destructive storm surge inland. A preliminary estimate from NOAA puts Ian’s damage at more than $50 billion, and damage estimates from some private insurers approach or exceed $100 billion. It’s likely that tens of billions of this damage was caused by a catastrophic storm surge of 10 – 15 feet, which leveled countless structures on the low-lying barrier islands just south of where Ian’s eye came ashore.
Had Ian hit a century ago, when sea levels were about a foot lower, the storm probably would have caused billions less in storm surge damage, judging by the results from two studies looking at storm surge damage from 2012’s Hurricane Sandy in New York. Taken together, the study results suggest that rising seas left a huge portion of U.S. coastal infrastructure – much of it built during the 20th century – vulnerable to storm surges.
Small increases in storm surge can cause huge impacts
A small amount of sea level rise – even just a few inches – can lead to significant damage during a storm surge event. Why?
To use a sports analogy, it’s because the interaction of a storm surge with a city is a game of inches and thresholds. Coastal cities are generally designed so that it takes a 1-in-100-year event (one that has a 1% chance of occurring in a given year) to cause substantial damaging flooding: A storm surge must rise to the base height of the city before it can flood large areas. But once the storm does cross that threshold, every inch of additional rise in water levels can flood large areas. And since just one inch of water in a 2,500-square-foot home can cause $27,000 in damage, and 12 inches can cause $72,000 in damage (according to FEMA), a few extra inches of storm surge can add up to a lot of damage in a hurry.
A higher storm surge makes deaths more likely
Since the storm surge plays a game of inches, a surge riding inland atop ocean levels swelled by human-caused sea level rise now has substantially higher odds of exacting a high death toll compared to a century ago. Ian is being blamed for at least 120 deaths in the U.S. – 114 in Florida, five in North Carolina, and one in Virginia. At least 58 of these deaths were from drowning, with the storm surge claiming the most victims. Human-caused sea level rise increased the odds of this high death toll.
To see how just a few extra inches of surge from human-caused sea level rise could have crossed a threshold responsible for killing someone, consider the case of the Hideaway Village Motel in Fort Myers Beach, where a USGS storm surge survey showed high water marks of 7 – 12 feet from Ian’s storm surge occurring on either side of the hotel. As Ian’s surge ripped the building from its foundation and carried it over a third of a mile, four hotel guests lashed themselves to a mattress that floated up to the ceiling; one died when the surge pinned her against the ceiling. If Ian’s storm surge had been a foot lower – as would have occurred a century ago, before human-augmented sea level rise occurred – the victim may well have survived, if the surge had not been quite high enough to pin her to the ceiling.
Figure 1. Preliminary high-water marks from storm surge plus waves from a USGS survey in October, 2022. (Image credit: Michael Lowry)
Figure 2. High-fidelity storm tide data from a pressure sensor mounted on the Fort Myers Beach Pier indicated a storm tide reaching about 13 feet above the pre-Ian beach, with waves helping water levels reach to 15 feet. The beach itself was scoured away by the powerful waves, losing about 5 feet of sand from pre-Ian levels. (Image credit: Michael Lowry)
Storm surveys of Ian’s damage revealed a 10- to 15-foot storm surge
The United States Geological Survey, or USGS, conducted a preliminary storm surge survey in the weeks following Hurricane Ian. Results indicate that the peak surge occurred in Lee and northern parts of Collier Counties, about 25 to 30 miles south of where the storm came ashore, near its radius of maximum winds of onshore flow. High water marks on Fort Myers Beach reached nearly 16 feet in spots, and the National Hurricane Center tweeted that based on the USGS survey, Ian’s surge reached 10 – 15 feet above normally dry ground there. High water marks of seven feet or higher above ground level were found along a 70-mile stretch of Florida coast from Cape Coral to Everglades City. (High water marks include wave action on top of the surge, and so are generally higher than the surge.)
Figure 3. Sea level rise since 1965 at the Fort Myers, Florida, tide gauge has been about 7.6 inches (0.63 feet), or about 13.3 inches (1.11 feet) per 100 years. Sea level rise has been accelerating due to human-caused climate change, substantially increasing storm surge risk. (Image credit: NOAA)
Sea level rise since 1965 at the Fort Myers, Florida, tide gauge has been 7.6 inches, or about 13.3 inches if extrapolated to a 100-year period (Figure 3). A substantial portion of this sea level rise has been because of human-caused global warming; the global sea level rise since 1900 is estimated to be about 7.5 inches (19 cm). Most of this rise has occurred because of melting of glaciers and because water expands when heated.
Hurricane Sandy of 2012: billions in extra damage from sea level rise
As much as $8.1 billion of the $62.5 billion in damage caused by Hurricane Sandy in 2012 in New York, New Jersey, and Connecticut resulted from the increase in sea levels caused by human-caused climate change, according to a 2021 paper by scientists from Climate Central.
Hurricane Sandy brought a storm tide (the combination of storm surge and the natural tide) of 9.2 feet (2.8 meters) to New York City, and the scientists calculated that if the storm surge had been just 3.8 inches (9.6 cm) lower, the surge in the Tri-state area would have affected 9.2% fewer people (71,000) and 8.8% fewer housing units (36,000), causing 13% less storm surge damage. They picked 3.8 inches as their threshold to study, since that is the amount of sea level rise that has occurred since 1900 in New York City that can be confidently attributed to human-caused global warming. (The total sea level rise that occurred from 1900 – 2012 in New York City is much higher, about 12.9 inches, since there are significant natural components caused by land subsidence and natural variations in ocean currents.)
The Climate Central study used FEMA’s estimate that essentially 100% of Sandy’s damage was from storm surge; a separate study by Lloyd’s of London (see below) estimated that storm surge was responsible for 65% of Sandy’s damage. Depending upon which estimate of the fraction of damage is used, between $5.2 billion and $8.1 billion of Sandy’s damage (13% of the total storm surge damage) was because of the increase in sea levels caused by human-caused climate change.
Climate Central’s analysis presented only a minimum estimate of the impact of climate change on damages from Sandy, lead author Ben Strauss said in an interview with Carbon Brief: “We didn’t look at the whole of Sandy, so we really see our estimate as a conservative, low-end estimate. We didn’t assess whether climate change made Sandy stronger or affected its path … But we isolated the effect of the higher starting sea level, and that’s just something we can stand on – it’s very rock-solid bedrock for understanding the impact of climate change.”
A separate study by Lloyd’s of London also found a large impact on storm surge damage for Hurricane Sandy from sea level rise – as much of 30% of Sandy’s storm surge insured damage in New York could be attributed to the 0.8-foot rise in sea level since 1950, the study found. Since damage in New York accounted for 40% of Sandy’s total insured losses of $20 – $25 billion, and 65% of those losses were from storm surge, this 30% increase in damage equated to a loss of $1.6 – $2.0 billion (2012 dollars). The total damages would be far greater, though, as the estimate was only for New York, and insured damages are typically only about 50% of the total damages. The study did not separate out the natural and human-caused portions of sea level rise, however.
With our cities built for a 20th-century sea level, 21st-century storms are now able to inflict much higher damages because of higher sea levels. According to an analysis of hurricane-prone coastal U.S. locations by Climate Central, what was once a 1-in-100-year storm surge event for over half of these cities is now a 1-in-33-year event because of sea level rise. Stronger hurricanes because of higher ocean temperatures creates an additional risk factor; the authors of a 2013 paper proposed that this change could lead to an additional factor of 2 – 7 increase in Hurricane Katrina-level storm surge events on the U.S. coast.
This dangerous shift in the climate makes a huge portion of our 20th-century infrastructure unacceptably vulnerable to risk. Strong action is needed to prepare our coastal cities for a future with higher storm surges and to prevent the situation from getting worse: A more rapid conversion to a clean energy economy that doesn’t burn fossil fuels is needed.
Things you can do:
1) Flood-proof your home. FEMA has some great suggestions on how.
2) Know your flood risk. The National Hurricane Center hosts storm surge risk maps that allow one to view the flooding above ground level for hurricanes at the five Saffir-Simpson scales. Be sure to look at not just your property but also the escape routes you would take in an evacuation to see if those roads might flood before your property does. Also, consult floodfactor.com, a tool first made available by the First Street Foundation in 2020, which allows one to type in an address and see the specific flood risk for that property. It’s a fantastic new resource of a kind that was never available publicly before and is free for noncommercial purposes. The tool also evaluates wildfire and excessive heat risk for your property.
3) Know your elevation. If you live near the coast, or are thinking of buying property near the coast, it’s very much in your financial and survival interests to know the exact elevation of your home. If you are a homeowner, your flood insurance certificate should tell you your elevation based on the best available USGS surveys for the area. If not, go to the U.S. Geological Survey website called the National Map Viewer, enter an address, or just zoom into the area of interest. This web site has detailed instructions on how to use the USGS tool to find your elevation.
4) Climate Central’s Surging Seas Risk Finder has some great resources for evaluating your storm surge risk. Here’s the detailed page for Fort Myers.
5) Support policies and vote for politicians that will deal realistically with the threat sea level rise poses to our hurricane-vulnerable coasts. Ultimately, sea level rise, combined with potentially stronger hurricanes, will make the cost of defending and insuring property in high-risk hurricane-prone coastal areas so great that a collapse of the coastal real estate market will occur, resulting in a mass migration away from the coast. The sooner this reality is acknowledged and planned for, the less expensive and disruptive it will be. Climate futurist Alex Stefen theorizes that although unlikely, it is possible that Hurricane Ian has already set this process in motion. Ian could cause a wave of revaluations in vulnerable places around the country, triggering investment pullbacks, loss of insurability, and local housing market crashes.
We should heed the words of Duke University sea level rise expert Dr. Orrin Pilkey and co-authors in their excellent 2016 book, “Retreat From a Rising Sea; Hard Choices in an Age of Climate Change”:
“Like it or not, we will retreat from most of the world’s nonurban shorelines in the not very distant future. Our retreat options can be characterized as either difficult or catastrophic. We can plan now and retreat in a strategic and calculated fashion, or we can worry about it later and retreat in tactical disarray in response to devastating storms. In other words, we can walk away methodically, or we can flee in panic.”