Climate change makes it 'wildly' misleading to call 'intense' Vermont disaster a '100-year flood'

21 July 2023

The Summer of 2023 has brought a variety of extreme weather, from heatwaves in Southern Europe and the southwestern United States to severe flooding in Vermont and the Philadelphia suburbs. Rome, Italy reached a record high of 108F on July 18 while results of Bucks County, Pennsylvania outside Philly were mourning the deaths of five people killed during flash floods.

Because of the flooding in Vermont, more than 100 people needed to be rescued. Those events followed a different problem that had been plaguing northeastern cities like New York, Philly and Boston during the summer: unhealthy air quality because of wildfires to the north in Quebec, Canada.

Reporters and meteorologists have been describing the flooding in Vermont as a "100-year flood." But journalist Jackie Flynn Mogensen, in an article published by Mother Jones on July 21, argues that climate change makes such language misleading.

Mogensen explains, "This year's floods have been historically intense. The storms that hit Vermont on July 10 — delivering more than five inches of rain in a single day and forcing hundreds to evacuate their homes — had a 1 percent chance of occurring annually, leading to a '1-in-100-year' flood. But thanks to climate change, what was once considered a '100-year' or '1000-year' rainfall may be wildly outdated, according to a new, peer-reviewed report from climate research nonprofit First Street Foundation."

The National Oceanic and Atmospheric Administration, Mogensen notes, has a tool called Atlas 14, which has been "widely considered the gold standard for atmospheric statistics" and is used to measure the severity of weather events.

But according to Mogensen, "The problem is, most of the data plugged into Atlas 14 hasn't been adjusted for climate change, says Jeremy Porter, First Street Foundation's head of climate implications — meaning it has failed to capture things like the rise in global temperature and humidity, which can cause more severe storms…. In the most severe cases, what was once considered a '100-year flood' in some parts of the country is happening every eight years. Case in point: Officials in Vermont have characterized the state's floods as on par with those during Hurricane Irene in 2011."

Journalist Lois Parshley, reporting for The Atlantic in an article published on July 20, warns that climate change may bring a "dramatic uptick in climate-related disasters" — and it could happen quickly.

William Ripple, an ecology professor at Oregon State University, told The Atlantic, "Many scientists knew these things would happen, but we're taken aback by the severity of the major changes we're seeing."

Similarly, Allegra LeGrande, a scientist at Columbia University in New York City, told The Atlantic, "For a long time, we were within the range of normal. And now we’re really not. And it has happened fast enough that people have a memory of it happening."

In a separate Atlantic article, also published on July 20, journalist Megan Mayhem Bergman stresses that Vermont, in the past, seemed less disaster-prone than other places.

"In 2020, a ProPublica analysis identified Lamoille (County, Vermont) as the one county, across the entire United States, that could be most protected from the combined effects of climate change, including sea-level rise, wildfires, crop damage, and economic impact," Bergman explains. "But that was before the floods. Earlier this month, five to ten inches of rain fell in Morrisville, near the center of the county. Roads were destroyed in nearby Wolcott. Thirty people were evacuated as floodwaters from the Lamoille River swirled around Cambridge."

Bergman adds, "Entire harvests were wiped out, and major roads became impassable. Jennifer Morrison, Vermont's public-safety commissioner, called Lamoille County 'the hardest-hit area' in the state."

Bergman points out that scientists have been trying to identify "climate havens": places less likely to suffer the effects of climate change. But Vermont, cited as an example of a "climate haven," has experienced a "string of extreme weather events this year" — including a "late-May frost" that "may have destroyed more than half of the state's commercial apple crop."

"Vermont is no longer the haven many believed it to be," Bergman laments. "And if this tiny, bucolic state isn't safe, far from the ocean in one of the coolest parts of the country, it's hard to imagine a place that is."

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