September 17, 2024
2 Minimum read time
Why are the Carolinas and Europe under water due to record rainfall?
On the other side of the Atlantic, both Central Europe and North Carolina were inundated by heavy rains.
A man walks on a flooded road in Mosbierbaum, Austria, September 17, 2024.
Christian Bruna/Stringer/Getty Images
Recent heavy rains and destructive flooding have hit central Europe and eastern North Carolina, with some areas receiving up to 18 inches (48 cm) of rain.
The flooding began on September 13 and spread across countries including Austria, Poland, Romania and the Czech Republic, with some cities reporting up to 18 inches of rain over the weekend. At least 22 people died. As rain continued to fall in Europe and across the Atlantic, another storm began to saturate the eastern Carolinas and Virginia. Some areas received more than a foot of rain in 12 hours on September 16, drenching areas still recovering from Tropical Storm Debby in early August.
Why did so much rain fall? Scientists point to two separate and unusual phenomena taking place on opposite sides of the Atlantic.
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The record rainfall in Europe was caused by what meteorologists call an atmospheric block. Under normal conditions, a powerful corridor of strong winds called the jet stream surrounds the North Pole, blowing mostly from west to east. Usually, the jet stream moves north and south depending on conditions, but sometimes this phenomenon is particularly pronounced.
“This meandering flow is really amplified,” says Tim Woolings, an atmospheric scientist at the University of Oxford. When that happens, the jet stream tends to stall, which can cause weather systems to get stuck in place. When those systems have a lot of water vapor, they often produce heavy rain.
“The atmospheric blocks are definitely rare events,” says Woolings. “We expect to see them once or twice a season,” he says. “It’s a bit of an unusual weather pattern, but it does happen.”
Noboru Nakamura, an atmospheric scientist at the University of Chicago, says the U.S. precipitation would have unfolded differently without the atmospheric blocking. Instead, the Carolinas were drenched by a rare flip in the direction of the prevailing winds.
Typically, weather systems in the United States move from west to east, like the jet stream. Nakamura says the low-level winds in the Carolinas reversed and blew from east to west. But that was caused by interference from a high-pressure system to the north. “This is an unusual situation,” he says. “It was definitely an anomaly.”
In both regions, warm sea surface temperatures (European rains come from the Mediterranean and Black Seas, while those in the eastern United States come from the Atlantic) allowed each storm to absorb large amounts of water vapor, contributing to the severity of the flooding associated with the rainfall. Scientists fear that such intense storms will become more frequent as the climate continues to change.
Woollings says current statistics are too complex to tell whether the atmospheric blocks that wet central Europe will become more common with climate change. But the consequences of such blocks are likely to be more severe as warm air that can hold more water vapor becomes more common.
“These types of events are not going away in the future,” said Woolings. “As we become more sensitive to heat and flooding, the impacts will only get worse.”
