Vermont’s flooding this week is historic. What role did climate change play?

Over the past three days, rainfall and flooding reached levels not seen in nearly 100 years in much of Vermont. 

Rainfall in Montpelier set an all-time daily record on July 10. And several gauges across the state reported record high river levels. But behind the anomalous weather, scientists and officials see a larger trend: climate change. 

Vermont experts interviewed by VTDigger said that, while it’s impossible to blame one unusual weather event on climate change, there is a clear link between increasing temperatures and extreme weather. 

“Yeah, this is totally the sort of thing we would expect to be happening in a warmer world,” said Janel Hanrahan, a Vermont-based research scientist with the nonprofit Research Triangle Institute International. Earlier this year, Hanrahan left a position as the chair of the atmospheric sciences department at Northern Vermont University’s Lyndon campus. 

In some parts of Vermont, rainfall and water levels even exceeded those of Tropical Storm Irene in 2011, according to Rebecca Duell, a Burlington meteorologist at the National Weather Service. 

The precipitation this week was “definitely very comparable to the amount of rainfall we got in Irene,” she said. “Our rivers were comparable to the stages we saw in Irene as well.”

Over the past few days, some Vermont waterways, including the Lamoille River in Jeffersonville and the Barton River in Coventry, reported record high water levels. But Duell noted that historical data is lacking: another infamous Vermont deluge — the Great Flood of 1927 — happened so long ago that data was not being collected at some state waterways, and she said those floods likely surpassed this week’s.

But either way, “this is extremely unusual for Vermont,” she said.

Experts see the flooding as a clear piece of a larger pattern: “This is an absolutely classic climate change event,” Bill McKibben, an activist and environmental studies professor at Middlebury College, said in a brief interview.

For one thing, scientists say, climate change means warmer air; warmer air holds more water vapor; and more water vapor means more rain. 

“The world is 70% ocean,” Hanrahan said. “And so if the atmosphere can hold more water vapor, it simply will because it has a huge source of it.”

In the Northeast, Hanrahan said, proximity to the Atlantic Ocean means that  “there’s just an endless, endless supply of moisture that can be picked up from the ocean. And so we’re in kind of this ideal location to just really get dumped on as our planet continues to warm.”

Another key factor: Vermont’s mountainous topography. As humid air moves upward along mountainsides, it cools and creates clouds, which can cause precipitation. 

“So when we’re talking about that additional moisture in the air because of our warming climate, we still need to remember that it’s not taking place in a vacuum,” said Lesley-Ann Dupigny-Giroux, the Vermont state climatologist and a professor at the University of Vermont’s Department of Geography and Geosciences. “It’s not taking place on a flat part of the Earth. It’s taking place in a very mountainous region.” 

Climate change is also believed to be disrupting the jet streams, bands of high-altitude air that play a key role in weather across the planet. Those disruptions contribute to extreme weather, said Nolan Atkins, the vice president of academic affairs at Vermont State University and former professor and chair of the atmospheric sciences department. 

“In a warmer world and a warmer climate, the impact on the general circulation of the atmosphere is such that it creates these more frequent and more intense weather events,” Atkins said.

At a press conference Wednesday, Federal Emergency Management Agency Administrator Deanne Criswell said that, during her roughly two years in the position, “I have seen an increase in records being broken, records that have stood for decades or even a century.”

All that means more frequent severe weather events, experts said, particularly flooding. Just last year, in fact, University of Vermont researchers published a study projecting that climate change will exacerbate flood damage in the state. 

Such events are “a reminder that the clock is ticking — maybe it would be more accurate to say that the bomb is ticking,” McKibben said in an email. 

Even in Vermont, which has been touted as a refuge from the worst effects of climate change, experts say the drenching rain and floods should still inspire discussion on how to mitigate — and endure — increasingly frequent extreme weather. Vermonters need to consider “how we do things differently, how do we plan differently, how do we make sure that everybody’s at the table?” Dupigny-Giroux said.  

“Some of these are going to be really, really difficult conversations,” she added.