Over the past week, the hurricane Helene and a regular rainstorm that preceded it drenched the southeastern United States with more than 150 trillion gallons of rain, an unprecedented amount of water that stunned experts.
That’s enough to fill the Dallas Cowboys Stadium 51,000 times, or Lake Tahoe once. If focused only on the state of North Carolina, this amount of water would be over a meter deep. That’s enough to fill more than 60 million Olympic-sized swimming pools.
“This is an astronomical amount of precipitation,” said Ed Clark, director of the National Oceanic and Atmospheric Administration’s National Water Center in Tuscaloosa, Alabama. In 25 years of working in the meteorological service, I have never seen a phenomenon of such geographic magnitude and such a volume of water falling from the sky. »
The damage caused by the rains is apocalyptic, according to meteorologists. More than 100 people died, according to authorities.
Private meteorologist Ryan Maue, a former NOAA chief scientist, calculated — using precipitation measurements taken in four-kilometer by four-kilometer grids — that more than 150 trillion gallons of rain would fall through Sunday on the Eastern United States, including 75 trillion liters in Georgia, Tennessee, the Carolinas and Florida due to Hurricane Helene.
Mr Clark carried out the calculations independently and said the 150 trillion liter figure is about right, and even conservative. Mr. Maue said that since his calculations, there may have been a few billion additional gallons of rain, much of it in Virginia.
Mr. Clark, who devotes much of his work to monitoring dwindling water supplies in the west of the country, said that to put the amount of rain in perspective, it is more than twice the combined amount of Water stored in two key reservoirs in the Colorado River Basin, Lake Powell and Lake Mead.
Several meteorologists believed it was a combination of two or even three storm systems.
PHOTO MIKE CARLSON, ASSOCIATED PRESS ARCHIVES
A woman kayaks in Saint Petersburg, Florida.
Before the arrival ofHelenerain had been falling heavily for days because a low-pressure system had “cut off” from the jet stream – which moves weather systems from west to east – and stalled over the South -East. This system channeled a large amount of warm water from the Gulf of Mexico. A storm that could not be named stalled along North Carolina’s Atlantic coast, dumping up to 50 centimeters of rain, recalled Kathie Dello, North Carolina’s state climatologist.
It is then necessary to add Heleneone of the largest storms in the last two decades, which accumulated a lot of rain because it was young and moved quickly before hitting the Appalachians, explained Kristen Corbosiero, hurricane specialist at the University of Albany.
It was not a perfect storm, but a combination of several storms that brought a huge amount of rain. These rains accumulated at high altitudes, between 3000 and 6000 feet. And when you dump billions of liters on a mountain, it has to come back down.
Ryan Maue, meteorologist
The fact that these storms hit the mountains only made the situation worse, and not just because of the runoff. According to meteorologists Clark, Maue and Corbosiero, the interaction between mountains and storm systems increases air humidity.
North Carolina weather officials said the highest total was measured at 80 centimeters in the small town of Busick. Mount Mitchell also received more than 60 centimeters of precipitation.
Before the hurricane Harvey of 2017, “I told our colleagues, you know, I never thought in my career that we would measure precipitation in meters,” Mr. Clark said. And after Harvey, Florencethe more isolated events in eastern Kentucky, parts of South Dakota, year after year we see events where we measure precipitation in meters.”
According to Mme Corbosiero and Mr. Dello, storms are getting wetter due to climate change. According to a fundamental law of physics, the air contains almost 7% more humidity for every degree Celsius and the world has warmed by more than 1.2 degrees Celsius since the pre-industrial era.
According to Mme Corbosiero, meteorologists vigorously debate the role of worsening climate change in the phenomenon Helene and on the part of chance.
In a rapid analysis, not peer-reviewed, but using a method published in a study of precipitation from Hurricane Harvey, three scientists at the Department of Energy’s Lawrence Berkeley National Lab determined that climate change had led to a 50% increase in precipitation during Helena in parts of Georgia and the Carolinas.
For Mr. Dello, the “footprints of climate change” are clear.
“We have seen the impact of tropical storms in Western North Carolina. But these storms are wetter and warmer. At one time, a tropical storm would have headed toward North Carolina and caused rain and damage, but not apocalyptic destruction,” he said.