Climate Report: "Extreme" Rainfall Events Ten Times more Likely in Transylvania

A study finds that large swaths of the nation are at greater risk of destructive rain than the federal government now says; in Transylvania, "100-year storms" can now be expected once a decade.

Image of flooding near Balsam Grove caused by 2021’s Tropical Depression Fred. (Screenshot from YouTube footage posted by meteorologist Reed Timmer.)

ROSMAN — This is what Tim and Tina Pressley have been through since they waded through knee-deep water in their yard to escape flooding caused by Tropical Depression Fred in August 2021.

They had to rip out inundated ductwork in their 108-year-old home and install new piping in their high-and-dry attic. They replaced water-damaged flooring and tossed out furniture harboring dangerous levels of mold.

They slept in a motel for two weeks immediately after the flood and then on their porch for two months during repairs. They will soon face another long stint out of their house, which is scheduled to be raised at least three feet to prevent future flooding.

But none of this loss or inconvenience is as bad as the gnawing anxiety they feel when heavy rains begin to pelt the metal roof of their tidy home flanked by flower gardens on Rosman’s Main Street.

“Every time, you’re sitting here worried, ‘Are we going to wake up and be flooded again?’ ” Tim Pressley said last week. “The worst thing is the mental part.”

Though the Pressleys say that the upcoming elevation of their house will relieve many of their concerns, residents of flood-prone areas of Transylvania County are right to fear future storms, according to a study released last week by the nonprofit First Street Foundation.

Fred brought the heaviest three-day rain recorded in Brevard since the deluge that led to the bursting of the Lake Toxaway Dam in 1916, and was classified in some parts of the county as a 100-year storm, with a 1-percent chance of occurring in any given year, according to the U.S. National Oceanic and Atmospheric Administration (NOAA).

But such projections are rooted in data from the cooler 20th century, First Street says; factor in the changed climate — warmer temperatures and the resulting increase in airborne moisture — and large swaths of the nation can expect such “extreme precipitation events” far more frequently.

And few counties in the country face as much increased risk as Transylvania County, according to the peer-reviewed study, which last week was the subject of a front-page story in the Washington Post. Here, once-a-century storms should now be expected to arrive once a decade, or ten times as frequently as currently predicted by NOAA, First Street says.

If local leaders can do little about federal rainfall projections or state-generated flood maps used to guide development in flood-prone areas, they can amend ordinances to significantly increase protection for new construction, flood administrators said.

Engineers, architects, contractors and insurers should also factor in the increased flood risk when advising clients or designing projects, these administrators said, especially because the First Street study is just the latest addition to a growing body of evidence that extreme rainfall has become more destructive and common.

“I’ve been in this field for about 30 years and this trend is just worsening,” Chad Berginnis, the Executive Director for the nationwide Association of State Floodplain Managers, said of the increase in extreme precipitation events.

“In the past decades I’ve noticed that our estimates are too conservative and that it’s happening faster than we thought, and those seem to be two pretty ominous trends when it comes to flooding.”

The Report

Map showing areas at increased risk for extreme precipitation events. The darker the blue, the greater the increase. (Map provided by First Street Foundation.)

The two biggest flaws with the current NOAA model, First Street says: it relies on old rainfall data and an assumption that “extreme precipitation does not change.”

Weather stations across the country began recording rainfall from an earlier, more benign climate decades ago. The more such years that are used to calculate precipitation averages, the less weight that is given to more recent and relevant measurements of increased rainfall.

The First Street analysis, on the other hand, focuses on 21st century rainfall data that reflects this trend. For example, in the past 20 years, 30 NOAA rain gauges have recorded two or more supposedly “1-in100-year events, and 13 locations . . . have reported 1-in-500-year events,” the report says.

Meanwhile, “Billion Dollar Disasters” — floods that have caused at least that amount of inflation-adjusted property damage — are occurring about three times as often as they did in the early 1980s, according to the study.

The underlying reason for both the increased frequency of major rain storms and Transylvania’s growing vulnerability? Warmer air holds more moisture, the report says, citing a study showing that with every additional degree Fahrenheit, air can hold about 4 percent more water vapor.

The areas facing the highest increased risk for extreme rains are ones where precipitation is most directly linked to water sources, including coastal regions, river valleys and the Southern Appalachians.

The historically heavy rains in Transylvania — ranked 15th for increased risk of extreme rainfall out of more than 3,000 counties in the lower 48 states, the study says — are the result of saturated air flowing north from the Gulf of Mexico. The air rises and cools as it hits the Blue Ridge Escarpment, releasing its moisture as rain.

This system’s potential to produce more intense precipitation was previously established in 2020’s North Carolina Climate Science Report, which predicted that the frequency of extreme rains in this part of the state will increase by as much three-and-a-half times before the end of the century.

“Based on the virtual certainty that water vapor in the atmosphere will increase as global warming occurs,” the report said, “it is very likely (bold original) that the risk of extreme precipitation will increase everywhere in the Mountains.”

One other flaw in NOAA’s model causes it to further underestimate the frequency and severity of these storms, Jeremy Porter, First Street’s Head of Climate Implications: The agency hasn’t updated its projections for the region that includes Transylvania since 2006, the dawn of the big-rain era.

For example, according to Brevard’s (sometimes spotty) historical rainfall records, the city never received more than 100 inches of annual precipitation before 2013 but since then has done so during three separate years.

Still another problem, Porter said, is that NOAA’s model calls for discarding high and low rainfall numbers as statistical anomalies, which especially distorts the historic record in places such as Transylvania, where highly localized cloudbursts are a common feature of the climate.

“The NOAA results are over-smoothed and lose the . . . extreme events that occur across the variable topography,” he wrote.

The Big Picture

Transylvania, like all North Carolina counties, is covered by flood maps generated by the state under the guidance of FEMA.

It’s a painstaking process, Terry Foxx, a planner with the North Carolina Department of Public Safety’s Division of Emergency Management, wrote in an email to NewsBeat.

Representatives of his division visit each county, conduct land surveys and “look at our state data in reference to high water marks, historic flood levels and river-gauge information,” he wrote, and all work is “done to (FEMA) standards, vetted and approved by them, etc.”

NOAA’s precipitation estimates, meanwhile, are the result of “scientific rigor,” including peer review and stakeholder input, which is why they have been relied upon by engineers and community planners for decades, the agency said in a statement to the Post.

This system is also due for a significant upgrade. Thanks to funding provided in 2021’s $1.2 trillion federal infrastructure bill, the agency is creating new nationwide rainfall estimates using an approach similar to First Street’s — accounting for recent changes in the climate and modeling future conditions.

But a few problems remain.

The state can only periodically update its maps and last did so in Transylvania in 2009, said Mike Owen, the county’s building director and flood administrator.

That means the maps don’t reflect recent changes in runoff patterns, he said, including those caused by construction of informal berms in floodways — zones that during high water serve as channels of the county’s creeks and rivers.

Many landowners don’t realize that such activity is prohibited by the county’s Flood Damage Prevention Ordinance and “could possibly put somebody else at risk or put them into a floodplain zone when they might not have been there previously,” Owen said. “Education is the main thing I would emphasize.”

Then there’s the lack of coordination between FEMA and NOAA, the First Street report said. Because FEMA’s flood mapping guidelines don’t account for rainfall, they greatly underestimates the risk of future flooding, the study said.

Even if FEMA mapping does eventually incorporate estimates from the upgraded NOAA model, those won’t available for a good while.

“NOAA projects that this work will not be completed until 2027 at the earliest,” the First Street Study says.

The Local Level

What can be done in the meantime?

Some of it comes down to individual action, Berginnis said. Anyone planning to buy, build or insure a structure in flood-prone areas should be aware of and adjust to the increased risk, he said.

That especially applies to designers of  expensive public projects such as bridges, Berginnis said. “I would definitely make sure there was enough money or resources to think about that design more carefully to ensure it will be resilient to future flood conditions, because bridges last for decades.”

Counties can also amend flood ordinances to add protection to new construction, said Nathan Pennington, Buncombe County’s planning director and a former board member of the North Carolina Association of Floodplain Managers.

The FEMA National Flood Insurance Program’s Community Rating System offers guidelines for measures that can lead to the potential reduction of community-wide flood-insurance rates from between 5- and 45-percent.

“It allows you to adopt higher standards for special flood hazard areas and it also results in flood insurance discounts,” Pennington said, who added that a goal of participating in the Rating System was included in Buncombe’s recently adopted comprehensive plan.

One potential upgrade recommended through the Rating System could particularly apply to Transylvania — raising the elevation requirements of new buildings constructed in flood-prone areas.

Receiving a permit to build in a Special Flood Hazard Areas, according to the county ordinance, requires one foot of “freeboard,” meaning the lowest usable part of any new structure must be built at least that far above base flood elevation.

That’s the minimum recommended by FEMA, but the city of Brevard and almost all the surrounding counties require two feet of freeboard. And Foxx said the state’s model flood ordinance recommends four feet.

Berginnis called increasing freeboard to at least two feet a “common sense way” for communities to address the growing risk of inundation.

“You basically know flood levels are going to increase. That goes without saying,” he said. “An extra level of protection is not going to hurt anybody and could prevent injury or loss of life.”

Remember Fred!

Tim and Tina Pressley in front of their home on Main Street in Rosman

County staff is not currently working on such a measure, County Manager Jaime Laughter said, and while County Commission Vice Chair Jake Dalton didn’t specifically say he opposes increasing the freeboard requirement, he did express skepticism about the idea.

“Flooding is not new to Transylvania County,” he wrote in an email. Dalton, an insurance broker with experience handling homeowner policies, also wrote that flood-insurance premiums mostly depend on the location and elevation of individual properties: “The rating based on location is predetermined (high risk, standard risk, low risk) to a high degree.”

And “any changes that are made to building construction result in additional costs,” he wrote, “and we already know what our housing costs are around here.”

Yes, bolstering the freeboard requirement would create up-front costs, Pennington said, but, for starters, more is at stake than just money.

“To me a flood ordinance is a life-safety ordinance,” he said.

Also, a relatively small investment up front can lead to far greater savings in the long run, he said. “If you look at bringing a house into compliance after the fact, it’s a heck of a lot more expensive than doing it from the get-go.”

In September of 2021, FEMA estimated the cost of Fred-related storm damage in Transylvania to be $26 million, Laughter wrote in an email, though that number is still being refined as claims are processed.

Some of the FEMA funds have helped — or will help — repair or protect the Pressley’s home.

Beyond trauma, the main feeling they took away from the flood was gratitude, they said. Sitting on their front porch last week, they spoke with amazement about the help they had received from churches, the Sharing House non-profit, and the teachers who arrived from Rosman High School soon after the waters had receded.

“We were standing out there in the yard and looked up the road, and it looked like an army,” Tim Pressley said of the squad of teachers offering to clean up flooded properties. “That’s what really blew our minds.”

They are also thankful for government disaster aid, they said. The Pressleys received a $9,800 grant to replace flooring and payments for three years of flood insurance, Tina Pressley said, and the cost of raising their home is expected to total more than $200,000.

Remember such stories about flooding, such accounts of their expense, damage and disruption, Pennington advised. More floods will come, he said, probably more often and with more intensity. 

“People always forget about floods. The thing they say that drives flood managers crazy is, ‘We didn’t flood last time,’ ” he said.

“Well, no two floods are alike and the thing that keeps floodplain managers up at night is that these rain events are becoming much more repetitive and significant and dropping much more precipitation.”

Email: brevardnewsbeat@gmail.com