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In two places on the same night, a storm that hit the Northeast this week brought rainfall at rates that should only be expected once every thousand years, or close to it.
The storm killed at least three people and caused widespread flooding. About 10 inches of rain fell over 12 hours Sunday in parts of Connecticut including Oxford and Southbury. About 35 miles away, about 6.7 inches of rain fell in three hours Sunday evening in Stony Brook, New York. Both events would have about a 0.1 percent chance of occurring within a year. According to federal precipitation probability data.
“There were two areas that had equally heavy rainfall, and it didn’t happen at the same time,” said Nick Basile, director of the Center for Weather Hazard Communications at the University at Albany in New York. “Either of those areas are noteworthy, and it’s interesting not only that we got two of them in the larger storm pattern, but also that they were back-to-back.”
It's impossible to pinpoint the impact of climate change on a particular event right away, but scientists said the double whammy of heavy rainfall fits a pattern in the Northeast, where more intense storms are increasingly likely.
“These thunderstorms are now carrying more rain,” said Mark Wysocki, who recently retired as a New York State climatologist.
For each degree of warming in Fahrenheit, The atmosphere can hold about 3% to 4% of moisture.In 2023, global temperatures were about 2.4 degrees Fahrenheit higher than in pre-industrial times, meaning today's storms could be stronger.
In fact, extreme precipitation events have increased dramatically in the Northeast. The 2023 National Climate Assessment found that days with heavy rainfall Rainfall of 3 inches or more increased by nearly 62% from 1958 to 2018.The number of days with at least 5 inches of rain doubled during that period.
Such storms put stress on infrastructure — roads, stormwater systems and pipes — that were designed for a more temperate climate.
“We need to be more concerned about flash flooding and how we think about future urban design and planning and so on,” Wysocki said.
Some scientists also believe that climate change is altering the behavior of the jet stream and making it more likely to High and low pressure areas stop or become blocked.This could lead to longer storms over one area, leading to increased humidity. But the research is preliminary and scientists are hard-pressed to prove or disprove with confidence.
In the Northeast this week, a slow-moving front brought thunderstorms with locally heavy rainfall, meaning some areas were hit exceptionally hard while others were relatively spared.
This is a relatively unusual situation for heavy rainfall, said Mona Hemmati, a postdoctoral researcher at Columbia University in New York City.
“This usually happens with hurricanes or hurricane remnants, and this was not related to hurricanes,” she added.
The storm has highlighted known shortcomings in infrastructure in the face of increasingly extreme conditions. In general, cities and towns in the northeast of the country are not designed for such heavy rains.
Basil said New York City's sewer pipes are designed to handle About 1.75 inches of rain per hourFlooding was expected to occur once every five years under those design standards. But now, heavy rainfall events are becoming more intense and frequent, meaning flooding is more likely in the city and other nearby locations with similar standards.
In Stony Brook, 3.79 inches of rain fell in one hour on Sunday.
“It was not surprising that we saw major flooding,” Bassil said.
Two people have died in Connecticut after being swept away from their cars by floodwaters.Another man died when a tree fell on his car. The rain prompted evacuations, water rescues and grounded flights.
Connecticut Gov. Ned Lamont said more than a dozen roads will be closed for extended periods.
This article was originally published on NBC News.com
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