September 17, 2024
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Why did record-breaking rains flood the Carolinas and Europe?
On the other side of the Atlantic, central Europe and North Carolina are both being hit by heavy rains.
A man walks through a flooded road after heavy rain in Moosbierbaum, Austria, September 17, 2024.
Christian Bruna/Stringer/Getty Images
Central and eastern North Carolina have been hit by torrential rains and devastating flooding in recent days, with certain parts of each region seeing up to 18 inches of rain.
Heavy rains began on September 13 and battered 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 were killed. As the rain continued to fall in Europe, across the Atlantic, another storm began drowning the Eastern Carolinas and Virginia. Some areas received more than a foot of rain in a 12-hour period on September 16, inundating areas still recovering from Tropical Storm Debby in early August.
Why is it raining so much? Scientists point to two separate unusual phenomena happening on opposite sides of the Atlantic Ocean.
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Europe experienced record rainfall due to what meteorologists call a “blockage of the atmosphere.” Normally, a powerful channel of wind called the jet stream encircles the Arctic and blows from west to east. Normally, the jet stream shifts north or south depending on conditions, but sometimes this phenomenon is especially pronounced.
“These meanders get really amplified,” says Tim Woollings, an atmospheric scientist at the University of Oxford. When that happens, the jet stream also tends to stagnate, which can keep weather systems stuck in place. When these systems contain lots of water vapor, heavy rain often results, he says.
An atmospheric block is “a fairly rare event. We expect this to happen once or twice per season,” Woolings said. “It’s a bit of an unusual weather pattern, but it does happen.”
Noboru Nakamura, an atmospheric scientist at the University of Chicago, said the rainfall in the US unfolded differently without the atmospheric blockade. Instead, the Carolinas were drenched by a rare reversal in the direction of prevailing winds.
Typically, U.S. weather systems move from west to east, following the jet stream. But Nakamura said the low pressure system over the Carolinas was moving in the opposite direction, from east to west, due to interference from high pressure further north. “This is an unusual situation,” he said. “This was clearly unusual.”
In both regions, warm sea surface temperatures allowed the storms to kick up large amounts of water vapor, increasing the intensity of rainfall and resulting flooding — in the Mediterranean and Black Seas that brought rain to Europe, and in the Atlantic Ocean that brought rain to the eastern U.S. Scientists worry that such storms with intense impacts could become more frequent as the climate continues to change.
Woolings says current statistics are too complicated to say whether climate change will cause air puddles like the one that flooded central Europe to occur more frequently, but the effects of such puddles are likely to become more severe as warm air that can hold more water vapor becomes more common.
“These types of events aren’t going away,” Woolings said, “and as we become more sensitive to heatwaves and flooding, their impacts are only going to get worse.”
