Recent flooding on various rivers in western North Carolina surpassed historic records dating back to 1916, as extreme rainfall during the last week of September resulted in destructive torrents of mud and debris.

This week, scientists highlighted the unmistakable signs of climate change influencing the heavy rainfall linked with Hurricane Helene. Over a span of three days, significant rainfall occurred across more than 200 miles of the Appalachian Mountains, extending from Georgia to Virginia.

The catastrophic impact of Helene has resulted in at least 184 fatalities due to its direct and indirect effects, primarily due to the devastating rain in mountainous areas.

A preliminary attribution analysis conducted by three scientists from the Lawrence Berkeley National Laboratory indicated that the intensity of the rainfall while Helene passed through these regions was made “up to 20 times more likely because of global warming.”

“Our best assessment indicates that climate change may have increased rainfall by as much as 50% in certain regions of Georgia and the Carolinas during Hurricane Helene,” stated Mark Risser, Joshua North, and Michael Wehner from the laboratory. They noted that while their method for attribution has been previously validated, their initial evaluations could undergo modifications.

Warm Gulf Waters Intensifying Rainfall

The Gulf of Mexico is currently experiencing record or near-record warm temperatures, which scientists believe are fueling storms with significant rainfall. This phenomenon is evident in models that contrast present-day hurricanes with those from the past century, supporting the principle that warmer air holds more moisture.

Similar patterns were recorded during Hurricane Harvey and Hurricane Ian, where scientists have identified comparable impacts from climate change.

“We anticipate that Hurricane Helene brought increased rainfall due to climate change,” stated Kevin Reed, associate provost for climate and sustainability at Stonybrook University, who is engaged in examining how warmer Gulf waters intensify hurricanes.

Another initial evaluation assessed the total rainfall throughout the three-day event and found that the heat in the Gulf likely contributed to both Helene’s rapid intensification and the extreme atmospheric river that commenced more than 24 hours before the hurricane made landfall. Together, these conditions resulted in severe flooding across the southeastern U.S.

This assessment, calling for further investigation, was released by ClimaMeter, a Europe-based organization employing a framework created by the Laboratoire des Sciences du Climat et de l’Environnement in Paris-Saclay. ClimaMeter’s analysis leveraged historical weather data from the last 40 years, examining low pressure systems.

The research team reported that “Hurricane Helene’s heavy rainfall was up to 20% more intense and the strong winds were up to 7% stronger” compared to the conditions from 1980 to 2000. They suggested that ocean oscillations in the Atlantic and Pacific together with human-induced climate change may have also contributed to these outcomes.

The ClimaMeter analysis emphasized that “This extreme precipitation occurrence was triggered by a significant atmospheric river that Helene transported from the Gulf of Mexico into the Appalachian mountains,” explaining that elevation in the mountains intensified the already severe weather.

Cautions from Climate Researchers

The ClimaMeter study included a cautionary note: “If greenhouse gas emissions are not reduced, these types of extreme weather events will become more widespread across the U.S., impacting areas and communities that have not previously experienced such events,” warned co-author Davide Faranda from IPSL-CNRS, France.

“The severe rainfall during Hurricane Helene has been significantly intensified by the burning of fossil fuels,” stated Faranda.

“Our study clearly shows that human-caused climate change is worsening the effects of natural disasters that have always taken place, but now with much more severe impacts,” explained Tommaso Alberti, co-author of the study. “In the case of Hurricane Helene, the severity of the heavy rainfall has increased notably due to carbon emissions from fossil fuels, and such events will more frequently affect areas that were once less susceptible.”