SSU scientist ties strong hurricanes to climate change

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José J. Hernández Ayala, born 30 years ago in Puerto Rico, grew up amid hurricanes.

In 1989, the storm named Hugo spoiled his first birthday party, an event he doesn’t remember.

But he recalls Hurricane Hortense flooding his hometown of Arecibo in 1996, when the family home was safely upslope on the mountainous island, crowned by the world’s second-largest radio telescope. 

Then came Hurricane Georges in 1998, when Hernández Ayala, then 10, and his family huddled inside as winds shook their home and electricity sparked from broken power lines outside. A neighborhood church was smashed against the mountains by the Category 3 tempest that was Puerto Rico’s worst — until Hurricane Maria struck with unsurpassed fury in September 2017.

Hernández Ayala, a geographer/climatologist whose specialty is extreme weather events, had just settled in as an assistant professor and Climate Research Center director at Sonoma State University. It had been 19 years since the last major hurricane, Georges, impacted Puerto Rico, and Hernández Ayala wanted to know how climate change might have impacted their frequency.

What he and a colleague learned was unsurprising, but a bit unsettling.

Their study, published in March in the journal Geophysical Research Letters, concluded that a warming climate had made events like Maria nearly five times more probable than they were in the 1950s.

The link between climate change and hurricane activity had been established by other studies, but bringing it literally home made an impact, said Hernández Ayala, a Santa Rosa resident who sometimes commutes to the Rohnert Park campus by bicycle.

He and his wife have some 250 relatives in Puerto Rico, an island about 1,000 miles southeast of Miami squarely in the path of hurricanes spawned in the Atlantic basin. 

“We’re worried,” Hernández Ayala said, sitting in his sparsely furnished, white-walled office on the third floor of Stevenson Hall. “We are going to see more of these events in he future.”

Hurricane Maria was a monster, the worst by far of the 129 storms that have impacted Puerto Rico since 1956, based on data from 35 weather stations cited in the study.

“Maria was off the charts in everything,” he said, bringing up multicolored precipitation maps on his computer monitor, with a diagonal line tracing the storm’s track across the 3,500-square-mile island, about the size of Mendocino County.

Officially designated a Category 4 hurricane, Maria packed wind gusts at a Category 5 level of 157 mph or more. Hovering near and over the island for three days, the storm dropped up to 40 inches of rain, triggering thousands of landslides in the mountains.

The hurricane’s eye lingered for 12 hours over Puerto Rico, surrounded by a thick ring — called the eye wall — packing the strongest winds and rain. It ran right over Arecibo, and Hernández Ayala, monitoring its path, had repeatedly warned friends and relatives there of the peril.

“My wife was just going crazy,” he said, because her family was reluctant to evacuate. They left in time after his final warning: “Get out now.”

Maria unleashed unprecedented flooding that swamped their home in 15 feet of water. The concrete structure was built for wild weather and survived, but everything inside was ruined.

The megastorm virtually destroyed the electrical grid and municipal water supplies for 3.4 million residents in a nation with a 45 percent poverty rate and a median income of less than $20,000 a year, making the U.S. territory poorer than Mississippi, the least well-off of the 50 states.

High winds stripped vegetation from the ground, making the aftermath “look like a nuclear bomb (had hit),” Hernández Ayala said.

The death toll from Maria, initially listed at 64, has since been officially estimated at 2,975 lives, making it the deadliest natural disaster in the United States in a century. Damage from Maria in Puerto Rico and the U.S. Virgin Islands is listed at $90 billion, dwarfing the estimated $8 billion cost of Hurricane Georges.

Recent studies — cited by Hernández Ayala and co-author David Keellings at the University of Alabama — had established a likely connection between the intensity of Atlantic hurricanes and human-induced climate change. A study by researchers at University of California, Berkeley said climate change had likely increased rainfall from Hurricane Harvey, which hammered the Texas coast in 2017, by at last 19%. 

The connection is natural, since rising sea surface temperatures are a key component of climate change. Warm water fuels hurricanes and promotes evaporation, adding moisture to the air that comes down as rainfall.

Sea surface temperatures during the hurricane season in the area where Atlantic storms form rose just over 2% between 1956 and 2017, a difference Hernández Ayala said doesn’t seem like much but it “promotes a more favorable environment for tropical cyclones to develop.”

His study found Maria was Puerto Rico’s wettest storm in 60 years, but he wanted to know what the future would be in a warming climate.

Plugging in variables, such as air and ocean surface temperature, cloud cover and atmospheric carbon dioxide, enabled him and Keellings to calculate that long-term climate trends had increased the probability of storms like Maria by a factor they estimated at 4.85.

“These results place Maria prominently in the context of extreme storms that have impacted Puerto Rico and indicate that such events are becoming increasingly likely,” their report said.

You can reach Staff Writer Guy Kovner at 707-521-5457 or On Twitter @guykovner.

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