State climatologist: Areas are vulnerable we didn’t think were vulnerable

EMBREEVILLE, Tenn. (WJHL) — He already knew plenty about the potential for catastrophic flooding in Northeast Tennessee, but even state climatologist Andrew Joyner was surprised at the amount of destruction the remnants of Hurricane Helene wrought.

“Sediment deposit of several feet in some areas, completely stripped land in other areas all the way down to the bedrock,” Joyner, an East Tennessee State University geosciences professor, told News Channel 11.

“People’s homes are not only gone, but the land they built their homes on is gone, and we saw that over large areas, certainly across Unicoi and Washington County and down into Greene County.”

Now, Joyner and colleagues at ETSU’s Geosciences Department say it’s a good time to dig into the data they’ve found — and for area leaders to use it to make the region more resilient in the face of extreme flooding. ETSU was designated as the Tennessee Climate Office several years ago.

“Realizing that this type of event can happen highlights areas that are vulnerable that we didn’t think were vulnerable and so those should be factored into future hazard mitigation plans and zoning, construction standards,” Joyner said. “Those are things that really weren’t planned for by no fault of local government or people that had built there.”

Indeed, as Joyner and others from ETSU have been out with drones and equipment assessing the flooding from a scientific perspective, they’ve determined something that probably won’t come as a surprise: this was no 100-year flood. Most of their work has been in the Nolichucky Valley, and they’ve concluded the flooding may have exceeded anything witnessed by humans since before Europeans arrived.

“We certainly think this event ranged between a 1,000 and 5,000-year event,” Joyner said. In scientific terms, that doesn’t necessarily mean such a flood couldn’t occur more than once in a millennium — it means the chances of it happening in any given year range from 0.1 percent to 0.05 percent, or one in a thousand to one in five thousand.

How did it happen?

Northeast Tennessee got a lot of rain, both in the leadup to Sept. 27 and on that day, but not enough to produce the kind of damage Joyner saw that rivals destruction from Hurricane Katrina in 2005.

Wil Tollefson, a senior lecturer in ETSU’s Geosciences Department and the associate state climatologist, said the big water fell in Western North Carolina.

“The Gulf has been record warm and so that water being that hot really fueled a lot of this storm,” Tollefson said. “That warmer air is able to hold more moisture as it has traveled up from the Gulf of Mexico. It definitely impacted the amount of rain that fell, especially on the North Carolina side.”

Tollefson said as wind blew up and over the mountains on the North Carolina side, “it basically wrings out all of the moisture that’s in that air. So you can think about that as like a sponge and it just squeezes out all that moisture on their side of the mountains.”

But Joyner noted that what happened in North Carolina, while it caused even more widespread destruction in multiple Western North Carolina counties, didn’t stay in North Carolina. The headwaters and even medium reaches of rivers like the Nolichucky, French Broad and Pigeon are in North Carolina. Those areas collected 15 to 20 inches of rain in the course of just a few days, compared to less than half that amount on the Tennessee side.

“All of the water falling at the headwaters and midstream all came down through our area,” Joyner said.

“That very fast water, lots of debris collecting from the tributaries and from that channel — the Nolichucky’s a very narrow gorge — specifically moving into our area.”

Joyner said the speed of the event took people by surprise, and the scope proved deadly and disastrous. Estimated property damage in Northeast Tennessee exceeds $200 million already, and the death toll on the Tennessee side of the mountains is more than a dozen.

“Most of those stream gauges weren’t in flood stage before 8 a.m. that morning on Friday,” Tollefson added. “By 11, they were reaching record flood stage.”

Building community resilience

Joyner said the geosciences department and the Tennessee Climate Office will continue collecting data in the community about everything from floods to droughts and wildfires. The group already had funding to build a “community resilience academy” in Washington County that would focus on a different hazard for each of the six weeks.

Now, he said, they hope to gather data from this catastrophe and “get a better understanding of people’s perceptions of risk, and then how the data informs, maybe changes that perception.”

While it’s difficult to see any positives from Sept. 27 right now, Joyner said he hopes leaders are more than ready to take advantage of what the climate office folks will have to offer.

“Really trying to understand what happened and how can we take this event and better prepare in the future, certainly reduce the loss of life, reduce the impact on the built environment and reduce our losses,” he said.

“So, better mitigation efforts, better planning, taking information now from this and other events to really better understand what a 100-year or 1,000-year event is.”

Part of that process should include plugging precipitation data from the past 20 or more years into calculations used in flood maps.

“The sooner we can update those the sooner we can understand how more recent events affect the 100-year, 1,000-year events depending on where you’re at,” Joyner said.

He noted that Asheville, N.C. experienced a flood in 1916 “comparable to what happened” in late September.

“No one alive had experienced that, and there’s this complacency that sets in the longer you have between these types of events. And so it’s a matter of being less complacent and really recognizing the risk and planning for those types of risk.”

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