Vermont winter flooding may become more common due to climate change – VTDigger

Vermonters were treated to warnings of incoming heavy rainfall over the weekend, a forecast that many feared could be similar to July’s torrential rains, quickly turning into a nightmare for thousands across the state.

The storms that hit Sunday and Monday were much milder than July’s floods, and there were no reports of injuries. Still, it caused massive flooding, prompting 12 rapids rescues, closing 120 schools and flooding many basements.

“I don’t think anyone anticipated the extent of the flooding,” said Mike Reichlett, superintendent of the Harwood Union Unified School District, which was particularly hard hit by the storm. Things happened very quickly.

Meteorologists say such December storms may become more common, driven by the warming effects of climate change. At the same time, the severity of such storms remains difficult to predict because of the challenges posed by the difficulty of predicting snowmelt and the dramatic impact of temperature changes in forecasting.

Those variables had residents, managers and state officials anxiously watching and waiting over the weekend, only for the storm to become more severe throughout the day Monday.

Leichlit said he checked the weather forecast early in the morning and knew it could be a challenging day with the amount of water they expected. At that time, he said, the National Weather Service had not issued warnings that would affect Mad Valley schools.

Students arrived at Moreton Elementary School at 7:30 a.m., but just before 8 a.m. the principal called Leichliter to say a river was forming near the school. They prepared to alert the family, but before they could, water began seeping into the school gymnasium. At 8:30 a.m., the bus arrived at the school and took the students home.

Later that morning, other schools in the area also closed.

The water was rough, he said. While buses did experience some flooding while taking students home, the flooding only got worse in the afternoon.

“School leadership took timely action so we don’t face further challenges in getting children home safely,” he said.

This week’s storm is far from the first time in recent history that wet snow has caused chaos.

Last December, just days before Christmas, a storm brought rain, wet snow and strong winds, leaving tens of thousands of Vermonters without power. Between then and now, scientists have recorded six weather events featuring wet snow, said Scott Whittier, warning coordinator meteorologist for the National Weather Service in Burlington.

“I’ve been here 30 years and it doesn’t happen more than two times a year,” he said.

Whittier said several variables collided during this week’s storm to create a more severe situation than the National Weather Service initially predicted.

The weather service predicted 1.5 to 2 inches of rain in Vermont, but the region received 1.5 to 2.5 inches, with some areas seeing as much as 3.5 inches.

The rain was heavier than expected because it started along Florida’s Gulf Coast, where warm ocean temperatures filled the air with moisture.

Warmer air has the ability to carry more moisture, said Jonathan Winter, an associate professor of geography at Dartmouth College whose research focuses on extreme precipitation in the Northeast.

He thinks the atmosphere is like a bucket. The warmer the air, the larger the bucket.

“When you have a bigger bucket, when you get the right conditions, you can get bigger precipitation events because there’s more fuel in the storm in the atmosphere and more water is transferred to the landscape,” he said. middle.

In Vermont this week, multiple areas of low pressure are also causing the air to rise and add existing moisture, producing heavier rainfall.

Whittier said much of the state is already covered in snow and it’s difficult to predict how much snow will melt during the storm. While meteorologists crisscross the state to collect as much data as possible on the depth of snowpack and its moisture content, they often rely on computer models to understand the big picture, and sometimes they don’t always capture the texture of the snowpack or how dense it is. The consistency of snow, he said.

He said the storm was the fourth heavy rainfall in four weeks, meaning the snowpack was relatively wet. What’s more, forecasters expect temperatures to be in the 40 to 50-degree range, but with temperatures in some places reaching into the high 50s and 60s.

The National Weather Service predicted an extra inch of rainfall as the snow melted, but the warm weather kept rainfall closer to 1.5 inches.

So if there’s an inch more rain than expected and a half-inch or more more snowmelt than expected, that’s an additional inch and a half of rain on top of the two to three inches. Whittier said that could lead to more problems.

All those factors combined, rainfall, snow and warm temperatures are the perfect ingredients to accelerate flooding, Winter said.

Let’s say you’re two inches from the sky, you’re probably two inches from the ground, like the snowpack itself, (then) you’re not really talking about a two-inch storm. “You’re talking about a four-inch storm,” Winter said.

A four-inch storm is harder to handle than a two-inch storm, especially when the ground is already saturated from the past few weeks of precipitation.

When we make predictions about floods, like river flooding, like rivers overflowing their banks, there are a lot of variables there. It became part art, part science, Winter said.

Still, the state appears ready, Whittier said. Officials deployed rapids rescue teams who were ready and able to assist with the rescue. Business owners prepare for storms with sandbags, but many don’t need to use them. Although the school had to close at the last minute, everyone seemed to get home in time to be safe.

All told, if the same storm moves 50 miles west, where 4 to 6 inches of rain fall, Vermont’s major river stems could see July flooding with up to 8 inches of rain in some places, Whittier said. said.

“We’re very lucky,” he said. We were always on the west side.

Winter said that while scientists don’t typically link single events to climate change, Monday’s storms are consistent with the types of storms scientists expect to become more intense and frequent as climate change progresses.

Leslie-Ann Dupiny-Giroux, a professor at the University of Vermont and a Vermont climatologist, said in an email that flooding can occur in any season, winter, summer, fall, and winter.

She wrote that this week, December 17 and 18, the rain lasted for nearly 48 hours. This prolonged event over unfrozen land caused river levels to rise to/or above major flood levels.

Whittier said Vermont is also experiencing more frequent snowmelt events. He said that while historically the melt season began in February and lasted until April, Vermont’s melt season has changed dramatically due to climate change.

“Even in December, we’re witnessing snow melt, like we just saw in this event,” he said. We also have other events happening in December. We had a few in January.

Winter said he might have scoured historical records and found storms like this before human-caused greenhouse gas emissions emerged. This type of storm may not be new, but it may be hitting Vermont more frequently.

It’s the frequency and intensity of storms, he said, referring to their association with climate change. I think that’s exactly what we expected.

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