Climate change making storms stronger and more dangerous in the US, shows analysis of Hurricane Florence
Climate change caused by humans is making hurricanes stronger and more destructive in the US. Climate change led to a 10% increase in extreme rainfall during Hurricane Florence in the US in 2018, and to a nine-kilometer increase in cyclone diameter, states a new report.
The work suggests that climate change is having a measurable effect on tropical cyclone rainfall occurring in the present, says the research team from Stony Brook University, Lawrence Berkeley National Laboratory, National Center for Atmospheric Research, and Pennsylvania State University.
According to researchers, changes in extreme weather, such as tropical cyclones, are one of the most serious ways society experiences the impact of climate change.
The study, says lead author Dr. Kevin A. Reed, provides additional evidence that the impact of climate change is not some far-off reality.
"I think the lesson learned here is that climate change impacts are here now. Weather and extreme weather events, like tropical cyclones, have changed in quantifiable ways," Dr. Reed, assistant professor, School of Marine and Atmospheric Sciences at Stony Brook University, tells MEA WorldWide (MEAWW).
"This work demonstrates the ability to communicate these climate change impacts to the public while an event is happening, as well as an opportunity to translate the results into a form that is more informative for policymakers, local planners, engineers, etc. when developing regional adaptation strategies for the future," he adds.
Florence, a North Atlantic hurricane, made landfall as a category 1 storm on the coast of North Carolina on September 14, 2018. After landfall, Florence's forward motion slowed as it dropped large amounts of rain throughout the region before moving farther inland on September 17, 2018.
The resulting inland flooding caused extensive damage and hardships for North and South Carolinians.
According to the US National Weather Service, Florence produced extensive wind damage along the North Carolina coast from Cape Lookout, across Carteret, Onslow, Pender, and New Hanover counties.
"Thousands of downed trees caused widespread power outages to nearly all of eastern North Carolina. The historic legacy of Hurricane Florence will be a record-breaking storm surge of 9 to 13 feet and devastating rainfall of 20 to 30 inches, which produced catastrophic and life-threatening flooding," says the National Weather Service.
"The hardest-hit areas included New Bern, Newport, Belhaven, Oriental, North Topsail Beach, and Jacksonville, along with Downeast Carteret County, or basically south of a line from Kinston to Cedar Island," it adds.
Two days before Hurricane Florence made landfall in the Carolinas in September 2018, the research team made public predictions, based on a numerical model, of how climate change would affect the intensity, size, and rainfall amounts of this dangerous storm.
A retrospective analysis of the characteristics of the storm after landfall has now allowed the same authors to examine the predictions of their model.
They found evidence that climate change did, as predicted, boost extreme rainfall during the storm. The extreme rainfall was increased by 10% due to climate change, and are linked to warmer sea surface temperatures and available moisture in the atmosphere.
The "fraction of rainfall accumulations of more than 30 inches" was increased by more than 7% of what it would have been without climate change, shows the analysis published in Science Advances.
The hurricane was nine kilometers larger (or a 1.6% increase in storm area) due to the effect of climate change on the large-scale environment around the storm, says the team.
However, the actual impacts were less extreme than what their initial approach predicted.
"In particular, the analysis suggests that climate change led to a 10% increase in extreme rainfall during the hurricane rather than the projected 50% increase, and to a nine-kilometer increase in cyclone diameter rather than the predicted 80-kilometer increase," says the study.
The model used for this work is the Community Atmosphere Model developed at the National Center for Atmospheric Research. "It is a comprehensive atmospheric general circulation model routinely used for both weather and climate simulations," says Dr. Reed.
"The methodology relies on running a large number of ensembles under both the actual and counterfactual conditions. After our initial statement (which was preliminary), we increased the number of ensembles from 10 to 100 and refined the analysis methodology to be more quantifiable, he adds.
He says while the initial "attribution statement" was conducted in the days leading up to Hurricane Florence's landfall, the detailed analysis in the paper was completed in the months following Hurricane Florence.
In their analysis of their earlier forecast, the team compared models of the actual storm with simulations depicting how the same storm may have manifested if humans had not changed the climate.
The researchers say that this approach can only evaluate changes to the storm itself, but not assess the probability that another Florence-like hurricane will occur.
While acknowledging some limitations on the predictive capabilities of their initial model, the researchers are confident that post-event analyses like theirs will help refine future models.
The team says it will improve the ability of scientists to provide the public with sound scientific estimates of how climate change will impact and contribute to extreme weather events.
"This new approach allows for the effective communication that the risks and impacts of climate change are here now," says Dr. Reed.
The researchers say a refined version of their model would allow scientists to look at how shifts in atmospheric and ocean conditions caused by climate change create more favorable storm conditions, as they do now.
More importantly, it will also enable them to model the impact of climate change before a hurricane makes landfall.