Hurricanes: Unprecedented extremes or new normal?

Hurricane Helen in the Gulf of Mexico on September 25th. Credit: NOAA’s GOES-16 satellite
When Hurricane Helen struck the Southeast in late September, it quickly became one of the deadliest hurricanes in the United States in the past 50 years, second only to Hurricane Katrina. At least 228 people died as a result of the storm. Helene was also one of the largest storms in decades, similar in size to Katrina, which was 400 miles wide. Unprecedented winds and rain battered Florida, Georgia, South Carolina, North Carolina, Virginia and Tennessee, leaving nearly 2 million people without power.
But what does unprecedented storms mean in a changing climate? How are hurricanes changing, what impact do they have, and what does the future hold?
Two representatives from Tufts University joined a group of 21 researchers from around the world who were given 48 hours by the World Weather Attribution (WWA) to conduct rapid research in the wake of Helen. I have joined. Erin Coughlan de Perez, a climate risk expert at Tufts University, explains how climate change is affecting the intensity of hurricanes like Helen.
cone of uncertainty
“As hurricanes intensify, one of the most important tools in our toolbox is weather forecasting,” said Coghlan de Perez, associate professor at Tufts University’s Friedman School of Nutrition Science and Policy.
Coghlan de Perez works with organizations such as the American Red Cross and the United Nations to incorporate climate models into contingency and financing plans for weather events such as storms, droughts, floods and heat waves. . In hurricane forecasting, the most likely path for a particular storm is marked by a “cone of uncertainty,” which is updated as the storm progresses.
“Thanks to excellent forecasting and early warning systems, people were deployed much earlier than Helen. So many people were evacuated, but this takes courage. Forecasts can mean the difference between life and death. ,” says Coghlan de Pérez.
But Coghlan de Perez also said hurricane ratings focus too much on wind speed, which determines hurricane category. Therefore, the categories have nothing to do with expected rainfall or storm surge from the ocean.
“One of the main reasons Helen caused so much damage is because of the water she dumped into North Carolina,” Coghlan de Perez said.
Climate change is increasing the amount of extreme rainfall caused by tropical cyclones. Warmer air holds more moisture at a rate of 6-7% per degree Celsius. In today’s warm climate, rainfall at levels brought by Helen occurs every seven years in coastal areas and every 70 years in inland areas.
According to the WWA report, climate change has increased rainfall by about 10% and probability of precipitation by 70% in the Appalachian region, and increased precipitation by 10% and probability of precipitation by 40% in the southern region.
The WWA report also notes that tropical storms that make landfall in the North Atlantic tend to meander through terrain at slower speeds and stall more frequently. This means that it can stay in the same area for a long time, producing more rain than other areas. You can do it in one place.
During Hurricane Sandy in 2012, rising sea levels due to climate change caused storm surges that directly caused $8.1 billion in additional damage. Storm surge prediction is based on many factors, but the key to predicting storm surge is determining eye location.
“In the Northern Hemisphere, storms move counterclockwise, so one side of the storm (the ‘dirty’ side) pushes water onto land, and the other side pulls water away from land,” Coghlan de Perez said. “But it’s very difficult to perfectly predict the position of the eyes.”
The 15-foot storm surge that hit the Florida coast during Helen broke records.
unprecedented extremes
The word “unprecedented” has many meanings. Hurricanes can strike at unprecedented times of the year. Wind speeds and rainfall amounts are likely to be at unprecedented levels. And hurricanes can strike in unprecedented places.
“To study unprecedented extreme events, we run our weather models thousands of times to determine all possible weather scenarios, only one of which we ultimately experience. “We look at what happened in other ‘worlds’ and factor that into our scenario planning,” Coghlan de Pérez says.
Due to climate change, a hurricane as strong as Helen is now 2.5 times more likely to occur, expected to occur once every 53 years, according to the WWA report. Its strength is determined by several complex factors, including sea surface temperature, air temperature, and humidity.
Due to climate change, Helen’s wind speeds on the Florida coast are about 13 miles per hour faster (or 11% stronger). Helen occurred because climate change has made ocean temperatures 200 to 500 times more likely. Climate change is also contributing to the rapid intensification of hurricanes.
When Helen formed, the Gulf of Mexico was 3.6 degrees Fahrenheit warmer than average. The storm rapidly intensified, going from a Category 2 to a Category 4 in just a few hours. Hurricane Milton, which hit the Florida coast a few weeks after Helen, was the third fastest-intensifying storm on record in the Atlantic Ocean, changing from Category 1 to Category 5 in less than a day. Coghlan de Peres said the rapid intensification will make predictions much more difficult.
The combination of extreme events such as heat waves complicates hurricane assessments. The highest density of power outages during Helen occurred in regions with the highest temperatures. After Helen made landfall, heat advisories were issued for many areas of Florida, with power out and people without air conditioning. Heatwaves are the leading cause of death from climate-related disasters in the United States
Vulnerability and risk awareness
According to the WWA report, in the 88 counties that declared a disaster after Helen, 30% of the population is below 150% of the federal poverty level, 29% are minorities, 16% have a disability and 6% own a car. I don’t have it. . 22% of the housing units were mobile homes.
Carolyn Van Sant, project manager at the Feinstein International Center and one of the contributors to the WWA report, said, “Identifying who the most vulnerable people are will help ensure that they are as safe as Helen and Milton.” “We can build systems that prevent us from being unduly influenced by things like this.”
Even being evacuated is a privilege. Van Sant points out that you may need to pay for a hotel or own a car, which can be made easier by working remotely and having some type of disaster insurance. However, whether someone has disaster insurance depends largely on their long-term risk perception.
Dr. Leah Poole, a student in the Friedman School’s Agriculture, Food, and Environment Program and one of the contributors to the WWA report, said that in 2021, Tropical Storm Fred brought flash flooding to the North Carolina Mountains, killing six people. Despite this, they had very low community risk perception.
According to the WWA report, flood insurance coverage was twice as high in Florida as in North Carolina.
Arashi’s future
According to the WWA report, if global warming reaches 2 degrees Celsius, storms similar to Helen will become 3% more intense and 25% more likely in Appalachia, and 3% more intense in coastal regions. The probability of this happening increases by 16%. .
“Most studies on climate change adaptation find that what we’re doing isn’t fast enough to keep up with our current climate, so even looking back, we can’t compare the current and the future. It doesn’t help you understand what’s possible. It’s like driving while looking “in the rearview mirror,” says Coghlan de Perez.
Despite the work still to be done, Coghlan de Perez remains hopeful.
“I think it’s very heartening to see how people have come together to not only respond to these hurricanes, but to prepare for them,” she says.
Further information: B Clarke et al, Climate change key drivers of the devastating impact of Hurricane Helen, which destroyed both coastal and inland areas, (2024). DOI: 10.25561/115024
Provided by Tufts University
Quote: Hurricanes: Unprecedented extremes or a new normal? (November 1, 2024) From https://phys.org/news/2024-11-hurricanes-unprecedented-extremes.html November 1, 2024 obtained in
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