At this point, flooding is our country’s most frequent and most expensive disaster.
In April 2023 alone, floods happened across the country — including in the land-locked states of Minnesota, Kansas, Utah, Tennessee and Colorado. It doesn’t matter if you live in one of these states or on a coast: Everyone in the United States can be affected by water.
Flash flooding can occur in any city, at any time, because these floods are caused by heavy storms and a surplus of stormwater. The rushing water can knock people down, carry away cars, tear out trees and destroy buildings.
“How many times have we heard people say, ‘I've been in this house forever. It's never flooded’?” says John Lopez, a coastal scientist and lifelong Louisianan.
Over the last decade, the United States lost an average of 110 people to flooding each year, and in 2015, as many as 189 people died.
Men are more likely to die from flooding than women, according to one study. People under the age of 30 are the most vulnerable because the majority of flooding-related deaths involve people intentionally walking or driving into floodwaters. It’s so bad in Texas that billboards flash “Turn Around, Don’t Drown” whenever there’s a major storm.
Currently, 71% of our planet is covered with water, but 3-4 billion years ago, the earth was probably submerged in water. Back then, there was almost twice as much water in our oceans and all of our continents were under water. Yes, even Mount Everest.
So if it’s happened before, could it happen again?
On the latest episode of Seeking a Scientist, Dr. Kate Biberdorf (aka Kate the Chemist) breaks down the flooding happening in the United States and learns what we can do to better prepare for a floodier future.
Why are floods more frequent?
It’s no secret our planet is changing. This last decade was the hottest on record. And as we continue to add more people and these people continue to burn fossil fuels, the Earth keeps getting warmer.
This warms up ocean water, melting glaciers and sheets of oceanic ice, which contributes to sea level rise. When we mix higher ocean temperatures with more water in those oceans, we see a lot of evaporation. And more water in the atmosphere at warmer temperatures creates the perfect combination for intense rainstorms, tornados or hurricanes.
And it’s not just that we are having more intense storms. Due to the extraction of underground resources, the land is sinking.
“In Louisiana, estimates vary, but probably at least half of the loss that we've had is probably attributed to oil and gas activities,” says Lopez.
When we drill for fossil fuels, we extract groundwater, thermal water, oil and gas from the subsurface, which can sometimes be several kilometers deep. This leaves an open hole underground that eventually collapses from the weight of the soil and dirt above it.
It’s not just the oil and gas companies causing these problems. In big cities, the weight of the buildings can physically compress the ground. New York City is sinking at a rate of about 1-2 millimeters a year, according to a study released in early May.
With the land sinking and sea levels rising, citizens along the East Coast and Gulf Coast of the United States have been reporting something that is quite bizarre: On bright sunny days, water is oozing out of the storm drains, flooding the streets and completely shutting down cities — without a cloud in the sky.
What is sunny day flooding?
This freaky phenomenon is called high-tide flooding, also known as sunny-day flooding, king-tide flooding or nuisance flooding.
This type of flooding can occur in coastal communities whenever there’s a high tide, which is caused by the moon. The moon’s gravitational pull on the Earth causes the ocean to bulge toward the moon. So, as the Earth rotates, the section of the ocean that's pulled toward the moon is the “high tide.”
On the beach, we can easily see this when the water moves far up onto the sand and drenches unsuspecting tourists who’ve put their towels too close to the water. Locals, of course, know that high tide is normal and only lasts for a short time before water recedes.
When we couple the high tides with more water in the ocean, we have sunny-day flooding.
“Right now, a lot of the East Coast and Gulf Coast communities in particular have had really high rates of relative sea rise,” says William Sweet, an oceanographer for the National Oceanic and Atmospheric Association. “These stormwater systems that we laid in the ground are now acting as conduits for water to sort of backflow and come up through the systems and spill out onto the streets.”
People living in coastal cities — like Boston, Massachusetts; Charleston, South Carolina; Miami, Florida; and Galveston, Texas — all experience sunny-day flooding with some regularity.
Each coastal city is different: Miami usually experiences three to seven daysof sunny-day flooding annually; Boston has been known to have 22 “Waterworld”-like days each year; and Eagle Point, in Galveston Bay, Texas, just set the record for 64 days of sunny-day flooding in one year.
In the past 20 years, the rate of sunny-day flooding has doubled. Compared to 2000, it’s increased 400% on the East Coast and 1,100% on the Gulf Coast. And the West Coast is next.
By 2050, La Jolla, California, and Honolulu, Hawaii, will catch up with Boston, scientists predict. All three cities are expected to have about 60 days of sunny-day flooding every year.
While the East and Gulf Coasts are coping with sunny-day flooding, the West Coast is dealing with an equally peculiar phenomenon: rivers of water in the sky.
What are atmospheric rivers?
Scientists call them atmospheric rivers, but they are basically flying water snakes. These “rivers” occur when water vapor (i.e. water in its gas phase) clumps in the air to form long tubes of moisture that are on average 250-375 miles wide.
One of the most notorious atmospheric rivers is the “Pineapple Express,” which earned its nickname because it brings moisture from Hawaii all the way to the western coast of the United States.
When the Pineapple Express hits the mountains on the West Coast, the water vapor rises up over the mountains and then rapidly cools to release a downpour of rain on the residents of Washington, Oregon and California. If it’s really cold, they get a blizzard instead of a thunderstorm.
Back in January 2022, the state of Washington had disastrous flooding after an atmospheric river dumped as much as six inches of rain on the state. In some areas, rivers crested at 18 feet, and it was so scary that the National Guard was activated to help evacuate citizens.
But that was nothing compared to the flooding in December 2010, when a network of atmospheric rivers dumped 10 to 26 inches of rain on the entire West Coast, as far inland as Arizona, Nevada and Utah. They had to use bulldozers to rescue creek goers and helicopters to save hikers trapped in canyons.
These atmospheric rivers were especially dangerous because they showed up after summer wildfires had covered the ground in ash, kind of like a tarp. So instead of being absorbed by the soil, excess water combined with the ash to generate menacing mudslides. The mud filled homes, buried cars and destroyed bridges.
Just this past March, mudslides in central California knocked out a levee and cut off power for thousands of people.
Are floodwalls the answer?
Often dealing with the fallout is the United States Army Corp of Engineers, a group of engineers tasked with solving the most complicated public engineering challenges across the country.
They’ve engineered rivers, lakes, locks and dams, and these days, they’re coming up with ideas for floodwalls to protect our coasts. In addition to protecting communities from floods, they want to incorporate natural features, like coral reefs or maritime forests, inside floodwalls to capture carbon.
These proposals for six- to eight-mile floodwalls are being debated in state legislatures across the country, but they have big price tags: $1.1 billion in Charleston; $2.6 billion in Norfolk, Virginia; and a whopping $119 billion in New York City (and an estimated timeframe of 25 years).
Taxpayers are asking: Is the big price tag worth it?
Seattle says yes. Its 1.7-mile floodwall, finished in 2018, was built to withstand water of up to 38 feet. And in 2021, when a bad storm was working its way toward Washington, residents worked around the clock to raise the wall even higher — to 41 feet tall.
It was put to the test when Seattle experienced its second worst flooding in decades. The Skagit River crested at 36.9 feet, but the city remained dry.
How can you prepare for flooding?
If you are buying a house or real estate on a coast, pull up NOAA’s Sea Level Rise viewer. It has layers of maps that show which coastal areas are most susceptible to sunny-day flooding. Spend a few minutes on their website — it’s better to be safe than sorry.
And once you determine the best location for your new home, consider buying an elevated house, or a home on a hill.
Then, work with your neighbors to build “green roofs” by adding plants to the bare roofs of your local buildings. In England, they’re learning that these green roofs retain 34% more water than traditional paved roofs, where the water just slides off the concrete surface and floods the area.
Another option is to talk your city developers into adding features like those in China’s “sponge cities.” In these places, patches of grass are built into concrete sidewalks so water drains into the soil more easily.
As a last resort, for a few million dollars, you can live in a tiny floating seahorse home in Dubai or on a sea pod in Panama.
Where can I hear more about this topic?
Listen and subscribe to Seeking A Scientist with Kate The Chemist, from KCUR Studios, available wherever you listen to podcasts.
Seeking A Scientist is a production of KCUR Studios, made possible with support from the Stowers Institute for Medical Researchand design help from PRX.
This episode was produced by Dr. Kate Biberdorf, Suzanne Hogan and Byron Love, edited by Mackenzie Martin and C.J. Janovy, with help from Genevieve Des Marteau.
Our original theme music is by The Coma Calling. Additional music from Blue Dot Sessions.
