Trees hold secrets of El Niño and hurricanes, scientists say

As the 2026 hurricane season proceeds and a strong El Niño may disrupt weather patterns around the globe, the world’s trees will be keeping records.

Tree scientists say the evidence tree rings store about past weather and climate events can be “thrilling.” The rings reveal not just a tree’s age, but information about the storms, droughts and wildfires it survived. In Alaska, Arizona and forests all over the world, tree scientists are steadily adding to a vast collection of data that chronicles natural disasters of the past and offers clues to the future.

Narrow tree cores – the diameter of a pencil – have been pulled from some of the planet’s oldest trees. The samples have helped extend records of past weather events centuries beyond modern satellite imagery, scientists say. Width, density and spacing in cross sections of the tree rings document floods, droughts and hurricane landfalls.

As the nation celebrates its 250th anniversary, tree scientist Nicole Davi marvels at still-living trees that were growing in 1776 and the stories they can tell.

People call such trees “witness trees,” said Davi, a professor at William Paterson University and adjunct scientist in the Tree-Ring Laboratory at the Lamont-Doherty Earth Observatory. “They were there, right?”

Finding the right trees

“Going out into the forest” is one of Valerie Trouet’s favorite things about her work, especially in remote areas high in the mountains.  

“You arrive and you see these ancient old trees, in a beautiful landscape,” said Trouet, a professor in the Laboratory of Tree-Ring Research at the University of Arizona. “You’re among these organisms that have been there for centuries, literally many generations before you’ve been there.”

When you see the rings, “it’s so exciting,” said Trouet, who wrote "Tree Story," a book published in 2020. Sometimes finding the right trees can be an adventure, hiking into forests and mountains to find the oldest trees, patriarchs that hold centuries of information.

Researchers study trees from specific regions, depending on the questions they’re working to answer. If they’re studying drought, for example, they want to see tree rings in regions that are drier, where growth is dominated by moisture. The U.S. Southwest is a perfect example, Trouet said.

The trees grow slowly most years, based largely on the moisture they receive in a growing season. In Tucson, trees grow a lot in wet years, but in dry years, they don’t have enough water to create new wood, Trouet said. The rings in those years are “really narrow."

Under a microscope, a core slice from trees that are sensitive to temperature change can illustrate historic volcanic eruptions, Davi said. Patterns can be seen in the reduced growth from blocked sunlight and regional cooling, she said. “It’s just amazing to see the volcanic impacts from Mongolia to Canada to Alaska.”

Scientists studying climate trends want to look at trees that don't grow as fast, such as boreal forests, she said.

Building historical records

Collecting tree ring data to study events like El Niño helps fill in the history before satellites were available, Trouet said.

With 50 to 60 years of data, and a cycle that spans six or seven years, that’s fewer than ten El Niños to study, she said. “That’s not a lot, especially for statistical analysis.”

Expanding the data by comparing cores from other regions where climate and rainfall patterns are strongly affected by El Niño can improve the analysis of frequency and interactions with other events, she said.

Tree ring samples taken in areas previously hit by hurricanes can reveal not only the impact of long ago storms, but also recent storms, Trouet said. For example, tree rings have helped show how Hurricane Harvey's intense flooding in Texas affected tree growth and how rain storms are intensifying.

Studies have shown that tree growth slowed in the year after a hurricane, she said. Trees that remain standing lose their leaves and big limbs, and that trauma shows in their rings.

Davi found evidence of hurricanes in “gorgeous” old, “stunted and gnarly” trees in coastal New York and New Jersey.

“The really big (hurricanes) don’t happen that often,” she said. “The longer record you have, the more reliable idea you have of how often these hurricanes happen."

Researchers also cross-reference tree information to understand how wildfires strike the Pacific Northwest during El Niño years and the Southwest during La Niña years, and use tree rings to study how expansive or prevalent wildfires were in the past.

Knowing trees are recording stories that reveal how resilient they are to traumatic weather events has been fascinating, Davi said. But she adds it’s “super exciting scientifically” to look forward to what more trees could tell us about events that shape our histories.

Dinah Voyles Pulver, a national correspondent for USA TODAY, covers climate change, weather, the environment and other news. Reach her at [email protected] or @dinahvp on Bluesky or X or dinahvp.77 on Signal.