Vermont flooding worsened by climate change, increasing rain

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Streets in Montpelier, Vermont and surrounding communities morphed into rushing rivers this week, a dramatic display of what could happen more often as climate change fuels heavier rainfall events.

While flooding at the scale seen in Vermont remains rare in individual communities, extreme rainfall events are happening more often in the Northeast and much of the eastern United States and are expected to occur even more frequently in the decades, several experts told USA TODAY.

Heavy rainfall events could increase in the Northeast by an additional 52% by the end of the century, a study from Dartmouth warned in May.

“The number of wet days that experience extreme precipitation – the top 1% of wet days – are increasing quite significantly,” said the study’s lead author Christopher Picard, a recent Dartmouth graduate.

These big increases in rainfall events, such as those with more than an inch of rainfall, aren’t just happening in the northeast, said Ken Kunkel, an atmospheric sciences professor at North Carolina State University. They’re happening in much of the eastern half of the U.S., as well as in other parts of the world.

“Globally, more places have seen increases in precipitation than not, and the evidence is pretty strong that it is due to warming,” Kunkel said. Flooding similar to or worse than that seen in Vermont this week has occurred in Japan, India, Russia, Spain and Turkey over the past week.

What happened in Vermont?

The weather service reported 9.2 inches of rain fell in Calais, Vermont, with rainfall amounts over five inches widespread in the region.

The Winooski River in Montpelier soared 15 feet higher in a day, according to preliminary information from the U.S. Geological Survey.
At one point early Tuesday, nearly 100 road closures were reported.

“While it’s difficult to decisively say anything about one event, this is completely consistent with increasing precipitation in the Northeast and part of that being driven by climate change,” said Jonathan Winter, associate professor of geography at Dartmouth.

Has it flooded like this before in Montpelier?

Yes. Although three of the four highest historic crests of the Winooski River at Montpelier have occurred since 2011, the river hit its record height in 1927.

Conditions this week were similar to conditions in 1927, with higher than normal rainfall the preceding month, Dartmouth said.

National Weather Service history shows:

Roughly 8.71 inches of rain fell over about 36 hours between November 3-4, 1927.
The Winooski crested at 27.1 feet at Montpelier, almost six feet higher than it crested Tuesday.
84 people died, including the Lieutenant Governor, still the greatest number of fatalities from a natural disaster in state history.
1,285 bridges were lost and hundreds of miles of roads and railroad tracks.
The flooding prompted the Army Corps of Engineers to build 3 flood retention reservoirs and dams in the Winooski River basin.

If it’s happened before, how can scientists and scholars say this rain is connected to climate change?

Because rainfall records of all types show the heaviest precipitation amounts are increasing, and occurring more often, the scientists said. And the models used to recreate these events in history show they can’t account for the increase in rainfall without the added impacts of climate warming.

USA TODAY chronicled the increasing rainfall in a 2021 investigation.

USA TODAY Investigation:How a summer of extreme weather reveals a stunning shift in the way rain falls in America.

“What we’re starting to see is a dramatic change in precipitation patterns,” said Mark Wysocki, a senior lecturer in meteorology at Cornell University and New York State Climatologist. Earth’s temperature has been increasing since the late 1970s, he said.

Over about 50 years or so in the Northeast, the number of rainfall events with 5 inches of rainfall has increased by about 100%, Kunkel said.

Others also have increased:

2-inch events – 40%
3-inch events – 57%
4-inch events – 84%

Winter, the Dartmouth professor, found the number of days in the northeast with 1.5 – 2 inches of rain increased by more than 50% over the past 25 years when compared with the first 25 years of the last century, Winter said.

All of this increase in precipitation is reflected in NOAA records, which show:

Seven of the 15 wettest years in the 127-year record in Vermont occurred between 2003 and 2019.
In neighboring New York, 9 of the 15 wettest years dating back to 1895 occurred between 2003 and 2021.
Annual rainfall in the Northeast region has been below the long-term average only twice since 2000.

Just because a similar event might have happened in 1927, does not mean that this week’s event in Vermont wasn’t impacted by climate change, said Kevin Reed, an associate dean for research at Stony Brook University’s School for Marine and Atmospheric Sciences. “In fact, you could argue that if the 1927 event was to have happened in 2023 it could have rained more than it did in 1927.”

What’s driving the rainfall increases?

Warmer temperatures affect the movement of the jet stream and moisture flow from the Gulf of Mexico and other large water bodies.

Hotter oceans put more warmth and more moisture into the atmosphere, Kunkel said. “When you have an opportunity for these big events, they have more water to work with.”

Record heat is occurring in the North Atlantic this summer. Marine heat waves covered 40% of the world’s oceans in June, and that number is expected to increase to 50% by end of summer.

An update of the country’s scientific National Climate Assessment is expected to be released in October or November.

While the report’s authors can’t yet speak specifically about the report, a draft released last year found “robust evidence that human-caused warming has contributed to increases in the frequency and severity of the heaviest precipitation events across nearly 70% of the U.S..”

The chapter on the Northeast region looks at the multiple ways precipitation is increasing, said its lead author Jessica Whitehead, executive director of the Institute for Coastal Adaptation and Resilience at Old Dominion University.

One paper cited in the assessment looked at increases in extreme precipitation since the 1980s, Whitehead said, and found the only way computer models can reproduce the increases is if human-induced carbon emissions are included.