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Tree rings can provide evidence of climatic variations, such as rainfall and droughts, throughout history, researchers find.
Each year, climatic data is recorded by tree rings – which are layers of wood that are added annually to a growing tree throughout the tree’s life.
Ancient tree provide historical records of downpours, droughts, and so on, which could help scientists figure out what climate trends to expect in the future.
Edward R. Cook, a dendrochronologist at the Lamont-Doherty Earth Observatory of Columbia University and his fellow researchers use trees to map ancient downpours and droughts across the globe.
A paper published in the journal Science Advance, talks about Cook’s latest map called “The Old Drought Atlas”, which covers Europe, the Mediterranean rim of Africa, and the Middle East. Other atlases that are available are the “North America Drought Atlas” and the “Monsoon Asia Drought Atlas”.
According to Cook, trees tend to grow differently depending on climatic factors like temperature, rainfall, and so on. A narrow tree ring suggests a dry year, while a wider ring indicates that the tree had more moisture in its environment for better growth.
Tree rings can also provide other climate information depending on the changes in wood density. Denser wood in the tree ring indicates a warmer summer, compared with a less dense ring that would signify cooler temperatures.
After analysing the tree rings, Cook and his colleagues found that about one thousand years ago – during medieval times – there were mega-droughts (or extended dry periods).
The drought atlas provides information about climate conditions associated with historical event, such as the Great Famine (1315 – 1317) when wet conditions led to great crop failure in Europe.
It is important to note that Cook and his team do not chop down the trees to extract the information they need.
“We use a device called a Swedish increment borer that extracts a long dowel-like piece of wood from the tree, about five millimetres in diameter,” Cook said.
The tree is therefore not damaged in any meaningful way. Cook says that trees live many years after that. He actually returned to trees he had sampled twenty years prior and they were doing just fine.
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