Welcome to the Reign of King Tide: 10 Things to Know about This Week’s Tidal Flooding

October 27, 2015 | 6:01 pm
Erika Spanger-Siegfried
Director of Strategic Climate Analytics

This week, the so-called “king tides” are rolling in atop elevated sea levels, courtesy of climate change, and the flooding is well underway. This morning, Charleston Harbor, SC saw what is reported to be among the highest water levels ever recorded there—higher than during Hurricane David in 1979, meteorologists said—and the resulting morning gridlock as roads flooded and were closed. Southeast Florida neighborhoods are flooding over a succession of high tides, not surprisingly. Flood warnings are in effect for the East, West and Gulf Coast locations and forecasts warn of flooding through the weekend in low-lying areas.

If it feels like, suddenly, this extreme-tide flooding is in the news a lot, you’re not mistaken. But unlike other stories that take their place, even for years, in the news cycle, this story is not going away. Indeed, the role of extreme tides in coastal communities and beyond is inexorably growing. Welcome to the tidal flooding years—the reign of King Tide. Here are a few things to know about the flooding on display this week:

Miami facebook

Southeast Florida residents are facing disruptive flooding this fall, over repeated days. Here, the Miami Herald (earlier today) invites Facebook followers to share their flood stories. Credit: Miami Herald

  1. The number of extreme tides and tidal floods is rising.

I’m guessing you know that. I blogged about it during last month’s tidal flooding, so I’ll be brief: tidal flooding events have quadrupled in some places in the last 30 years and according to both UCS and NOAA analysis we can expect substantially more of them in just the next couple of decades. In some cases, a 10-fold increase in the annual number of tidal flood events can be expected in 30 years’ time. This is happening because there’s more water in the ocean and, when the combined gravitational pull of the sun and the moon drives the tides higher (and lower) than average, that water has no place to go but onto otherwise dry land.

  1. 2015’s “emperor tides”: many of them, and bigger than expected

In cities getting used to king tide flooding, some of the tides we’re seeing recently and in the coming months may be surprising, with deeper, more extensive flood water, and recurring floods day after day. This was Southeast Florida’s experience last month when the extent of flooding took most people by surprise. “Emperor tides”, let’s call them, are expected on both the West and East Coasts of the U.S. through this spring.

But why?

The leading explanation comes from Dr. William Sweet, an oceanographer with NOAA, who points to El Niño. It works in different ways on those two coasts. In the Pacific, the connection between El Niño and sea level is more direct. Easterly trade winds normally blow strongly across the equatorial Pacific, causing warm water to pile up in the western Pacific and making sea level higher in the western Pacific than the eastern Pacific. When an El Niño occurs, it’s like a seesaw leveling out. The warm water that was piled up in the west sloshes eastward (and poleward) and raises sea level in the east. Add to this physical redistribution of water the fact that warm water takes up more space than cool water (when you heat water molecules, they get bigger!), and you have two reasons why El Niño brings higher sea levels.

On the East Coast, it’s more complicated, but it basically boils down to this: El Niño alters atmospheric pressure patterns and creates conditions where winds out of the North and Northeast prevail along large stretches of the coast for extended periods of time. This does two things: it pushes water ashore and causes it to “pile up” there, raising sea levels for months at a time, and it favors the development of nor’easters, which can cause flooding.

Sea levels are forecast to remain elevated through the winter and into spring, as El Niño continues to influence weather patterns. During that timeframe, the communities NOAA examined “may experience a 33 to 125 percent increase in the number of nuisance flooding days”. To provide a specific example: Sandy Hook, NJ, saw on average two days with tidal flooding in 1960. With sea level rise it now sees about 26 such days. In the period between May 2015 and April 2016, because of El Niño, NOAA forecasts 40 tidal flooding days.

As Dr. Sweet puts it “you take a high rate of sea level rise, you add astronomical high tides on top, then you throw in some atypical behavior by the Gulf Stream and prevailing winds, and we can be surprised by some pretty extensive sunny day flooding”.

Just when you think you know a planet…


Bluffton Oyster Company (Bluffton, SC) this morning, October 27th, as floodwaters rose. Credit: Photo submitted to the Island Packet by Chelsea Burdette.

  1. These tides can do more than get things wet.

More than just “water where you don’t want it”, tidal flooding brings salt water onto roadways and into yards and houses, which can damage automobiles, damage homes and belongings, destroy lawns and landscaping, etc. Here in Massachusetts, my uncle lost his truck to repeated trips through tidal flooding along the only access road to his and hundreds of other homes. In North Carolina last month, as I mentioned in an earlier blog, homes in one neighborhood were completely surrounded by tidewaters that washed away fences and stairways. When higher tides with a little wave action meet a natural or man-made barrier, like beaches, dunes, or seawalls, they can also cause erosion.

  1. Before I pay off my mortgage, king tides will be much bigger, 5. Last longer, and 6. Become an issue along most of the coast

I’ve blogged on this, too, so see here for more info. But in a nutshell, in 30 years, more than half of the 52 communities UCS analyzed in our 2014 report can expect much larger areas to flood during astronomical high tides than today. As sea levels rise, an increasingly large portion of the daily tidal cycle will unfold on normally dry land, thus flood conditions will last longer. Thirty years from now, more than one-third of the locations we examined can expect flood-prone areas to be underwater 5 percent of the year.

The East and Gulf Coasts are vast, and we could look at only those 52 locations, but the fact that the rise in flood frequency is accelerating across most locations suggests that many places in between will need to brace for similar changes.

Welcome to the reign of the king tide.

  1. “Pawn” tides will grow to be kings, forcing some hard questions

The way we get from 10 flooding events today to 240 in 2045 is that higher sea levels enable even garden-variety tides to reach inland. In 30 years, we project Annapolis, for example, will face more than 360 tidal floods a year, or roughly 30 a month, without substantial adaptive measures. Let’s play this out: So, in a typical month, these floods would tend to cluster around the new and full moon, bringing flooding over roughly 15 high tides. Closest to the new or full moon, we would expect some floods to be quite extensive; farther away, the extent of flooding would taper off. Viewed over a month, this could add up to roughly “one week on” and “one week off”.

This scenario begs the question: though some low-lying flood-prone areas would not be permanently under water by 2045 (or even 2085), some could flood so often that for all practical purposes, they would be ceded to the sea without big measures to deal with the water. As FEMA Deputy Administrator, Roy Wright, said at a coastal flooding summit this past weekend, communities will need to decide what they can live with, as well as what they can’t live without.

  1. A surprising amount of… everything is within reach of a rising high tide line


    Hampton, New Hampshire (site of the recent Rising Tides Summit) during a previous king tide. Credit: Mike Barron

In this country, many people live within 3 feet of elevation of today’s high tide line—more than 1 million people in Florida alone, and the number is growing all the time. (So, add three feet to local sea level and those people’s neighborhoods are inundated. We could do that in relative short order.) At last count, 123 million people, or 40% of all Americans, lived in coastal counties. And if you put those coastal counties together (including the Great Lakes), they would represent the third largest economy in the world. A two-foot rise in sea level would put more than $1 trillion of today’s property and structures in the U.S. at risk of inundation.

Today, in fact, UCS released a report that speaks to the vast exposure of vital infrastructure to sea level rise and coastal flooding. Lights Out? looked at the electricity infrastructure in coastal zones and analyzed the exposure of power plants and substations to storm surge, today and in our sea level rise future. The results are a sobering reminder to take every opportunity to build infrastructure resilience, both to the major storm strikes and the gradually rising sea.

  1. Unlike hurricane landfall and storm surge, tides like this are baked in the cake.

This week we mark the third anniversary of Hurricane Sandy, with the knowledge that people are still struggling in the aftermath and, for many communities, things won’t ever be the same. In light of the lasting damage of this and other storms, our willingness to continue to invest in at-risk areas is… a problem. Psychology, economics, politics and more are at play here. But even as we try to untangle those and ensure that coastal decisions reflect real risk, we should remember that unlike hurricane landfall, the upward and inland march of the tides is already in motion and accelerating.

A major reduction in greenhouse gas emissions, which the world hopes its leaders will achieve in Paris later this year, could slow the rate of acceleration and thus curtail land loss and other impacts later this century and beyond. But the sea level rise and tidal flooding of coming decades? We already bought it.

  1. Across parties and regions, more and more local leaders get it

As I wrote earlier today, I spent this past weekend with a bipartisan group of 40 elected officials (19 Republicans, 17 Democrats, and a handful of independents) from coastal communities around the country who met to share experiences, advice, and ideas for the future in light of the growing threat of coastal flooding. Those 40 people are back home now, and it is flooding today, under sunny skies, in places on the West, East and Gulf Coasts. As I scan the National Weather Service flood advisories I see one after another of their regions affected. I’d like to give a nod to their hard work and leadership. And though the rest of us can’t make this problem go away, we can demand the same hard work and leadership on climate change, sea level rise, and coastal flooding from our federal leaders, too.

Beaufort Oct 2015 king tide 2

The downtown waterfront in Beaufort, SC, during Tuesday morning’s high tide. Beaufort Mayor, Billy Keyserling, will have recently returned there from this past weekend’s Rising Tides Summit in New Hampshire. At that meeting, he spoke with urgency about his community’s work to identify and address coastal flooding hotspots. Credit: Jeramie Stanley