Nation/World

Tennessee floods show a pressing climate danger across America: ‘Walls of water’

Janet Rice never suspected that Trace Creek could get so high. It would take an ocean surging 500 miles from the coast to her rural town in middle Tennessee.

Then the weekend happened. More than 17 inches of rain fell in a single day Saturday, overtopping the region’s many rivers and submerging places not previously considered floodplains within a matter of hours. Rice’s family business, a feed store that had stood for a century, was ripped in half. At least 21 people are dead, hundreds of homes are in shambles and the wreckage of people’s lives is strewn across the landscape.

“An ocean did come through,” Rice said.

Tennessee’s flash floods underscored the peril climate change poses even in inland areas, where people once thought themselves immune. A warmer atmosphere that holds more water, combined with rapid development and crumbling infrastructure, is turning once-rare disasters into common occurrences. Yet Americans, who often associate global warming with melting glaciers and intense heat, are not prepared for the coming deluge.

Inland flooding is the leading cause of deaths associated with tropical cyclones in the past 50 years, according to the Federal Emergency Management Agency. On average, damage from inland floods costs more than any other severe weather event. It’s a problem from the mountains of western North Carolina, where Tropical Storm Fred killed five people last week, to the streets of Dearborn, Mich., where heavy rains have repeatedly overwhelmed the sewer systems and destroyed homes.

“There is no place in the United States where you shouldn’t be resetting your expectations about Mother Nature disrupting your life,” said Roy Wright, president of the Insurance Institute for Business and Home Safety and former head of FEMA’s National Flood Insurance Program. “Climate change has come barging through the front doors of America.”

For years, scientists have warned that humanity’s greenhouse gas emissions, primarily from burning fossil fuels, would raise the risk of flooding around the country. Along coastlines, sea level rise has boosted high tides and increased the occurrence of sunny day flooding. The hotter oceans give more energy to hurricanes, accounting for the growing number of storms that rapidly intensify to category 4 and 5 events.

Melting glaciers may suddenly collapse, unleashing torrents of rock, water and ice. Intense heat waves in the spring and early summer can accelerate snowmelt, sending icy waters cascading through communities. This happened in British Columbia in June, when record-smashing temperatures led to widespread flooding along the province’s many mountain streams.

The most widespread danger is from an unrelenting downpour, the kind that swells rivers and saturates the soil. This can occur during hurricanes along the East Coast or monsoons in the Southwest, but climate change makes it possible even during a regular rainstorm. A physical phenomenon known as the Clausius-Clapeyron equation shows that for every 1 degree Celsius (1.8 degrees Fahrenheit) of warming, the atmosphere can hold 7% more moisture. Because the relationship between temperature and moisture isn’t linear, even small amounts of warming can create exponentially wetter storms.

The complex array of factors that contribute to a flood can complicate efforts to quantify climate change’s role. But research shows that warming makes events significantly more extreme.

A new study of the July floods in Central Europe released this week found that climate change has intensified downpours in the region by as much as 19%. The floods, which killed more than 220 people, were between 1.2 and 9 times worse than they would have been in a world unaltered by people, the scientists said.

The flooding in Waverly, Tenn., where Rice lives, has no precedent in the historic record. Retired National Oceanic and Atmospheric Administration hydrologist Geoffrey Bonnin said the chance of so much rain falling in such a short period is less than 1 in 1,000.

It’s yet another example of how climate change has loaded the dice for disaster, experts say. The floods that people lived through in the past are no match for the events that are happening today. And what in 2021 seems like an unprecedented catastrophe may by 2050 become an annual occurrence.

“I don’t like the way people have kind of used climate change as an excuse to not prepare,” said Hannah Cloke, a climate scientist at the University of Reading. “We should be very aware that climate change is here, and we need to take some action to get ready for things that haven’t happened before.”

That work starts with emphasizing how dangerous floodwaters can be, she said.

When rainfall exceeds a landscape’s capacity to absorb it, the water starts to gush toward the lowest point it can reach. Steep hills and narrow canyons will accelerate the flow, while converging tributaries can funnel rain that has fallen across a vast area into a single spot.

“These walls of water cascade with so much power and pick up everything in their path,” Cloke said.

Even 6 inches of moving water can knock a healthy adult over. A foot will sweep them away entirely. Since 2011, according to the National Weather Service, more than 1,000 Americans have been killed by floods.

In Tennessee, families described waking in the middle of the night to the sound of floodwaters surging into their homes. People attempting to drive to safety drowned when the torrent swept away their vehicles.

These are signs that scientists and public officials need better ways to educate people about flood safety, Wright said. Sirens could be used to issue warnings when people are asleep and communication systems are down. Every American should know that it isn’t safe to drive through standing water.

“I think the biggest gap for us is on the risk communication side,” Wright said. “We’re not bigger, stronger or smarter than Mother Nature. . . . We need to provoke people to take the action that’s needed for them to live through an event.”

Saving lives from floodwaters means taking steps in the hours, days and weeks before an event. But protecting homes and businesses will require long-term effort.

Human development has exacerbated the effects of climate change, said Vanderbilt University civil and environmental engineer Janey Camp. The flooded area, just 60 miles from Nashville, is in one of the fastest-growing parts of Tennessee.

As more and more ground gets covered with “impervious surfaces” like asphalt roads and concrete roofs, rain has fewer and fewer ways to soak into the Earth. Fixes to storm water and sewage systems have not kept pace with rapid development.

“Utilities and public works departments and local governments and state agencies managing infrastructure are just really struggling to make ends meet,” she said. “Its more about fix what you can with the resource you have as opposed to looking long term.”

A recent analysis by the American Society of Civil Engineers gave the nation’s wastewater systems a D+ grade. The bipartisan infrastructure package, which passed the Senate this month and is awaiting a House vote, would spend $55 billion to improve these systems.

If upgrades take into account the possibility of worse flooding as the planet continues to warm, Camp said, “then the decisions we’re making today can alleviate problems 20 or 30 years from now.”

Homes and communities can also be redesigned to make floodwaters less destructive, said architect Ed Barsley, founder of the U.K.-based Environmental Design Studio. Paved, impervious surfaces can be converted into green spaces that hold excess water. Buildings can be raised on stilts. Natural resources departments and land management agencies might even consider restoring waterways that have been straightened for industrial purposes; the more a river is allowed to twist and wind, the slower water will flow.

And there are scores of simple measures homeowners can take to make floods less costly. Installing heating and electrical equipment in attics or on roofs, rather than basements, could protect them from water damage. Replacing insulation with less absorbent materials may avert the need for major renovations.

Barsley recently toured a riverside home where wooden kitchen cabinets had been replaced with waterproof stainless steel — one less thing to worry about the next time the waters rose.

“I expected it to look like the back kitchen of a chip shop,” he said, laughing. “But it actually looked really good.”

It was a reminder to him that adapting to climate change can be about more than simply averting disaster. It’s an opportunity to build something beautiful.

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The Washington Post’s Abby Lee Hood in Waverly, Tenn., contributed to this report.

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