Back-to-back Amazon droughts trigger record forest stress

Paul Arnold

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Two back-to-back droughts in 2023 and 2024 caused the most severe decline in forest moisture and biomass (the total mass of living vegetation such as leaves, trunks and branches) in the Amazon since 1992, according to a study published in the journal PNAS. And many of the hardest hit areas are unlikely to recover before the next major drought arrives.

The rainforest is one of the planet's largest carbon stores. However, due to climate change, this vital planetary system is under intense pressure, particularly from increasingly frequent and more severe droughts.

A new way to track the forest

Typically, the Amazon experiences major drought events approximately every seven years. Measuring their effects usually involves forest surveys and satellite imagery, but these methods can be limited in scale or miss deeper forest changes due to cloud cover or rain.

So a research team developed a novel way to track forest health by compiling a long-term dataset using monthly microwave radar data to measure forest moisture and biomass. The advantages of this technique are that radar can see through cloud cover and detect water stored inside the forest canopy.

Instead of just looking at the color of leaves, which can give a false impression of forest health, radar signals interact with water inside trunks and branches. This tells scientists how much biomass and water are present, depending on the strength of the signal coming back.

Record-breaking decline

Using their dataset, the team compared the 2023–2024 droughts to every other major dry spell since 1992. They found that the sharpest drop in forest moisture and biomass occurred during those two years. Specifically, more than a quarter (26.8%) of the forest reached its lowest moisture/biomass levels in three decades. For comparison, only 11% of the forest reached similar lows during the 2005 drought.

"During the 2023–2024 droughts, the satellite radar scatterometer signal of Amazonian rainforests reached its lowest level since 1992, suggesting substantial alteration in forest functioning, including forest moisture and biomass," wrote the study authors in their paper.

To see what might happen in the future, the researchers used a computer model to predict how the forest would recover. The results overall were not encouraging, as they note:

"Model projections indicate that the postdrought recovery of the 2023-2024 event will likely be the lowest of all major droughts recorded since 1992."

A glimmer of hope

Despite that, it's not all bad news. The study also found that some parts of the forest are better at bouncing back. These areas share common traits, such as having shorter trees, sandier soils and trees growing in poorer soils that tend to be more drought-tolerant and better able to cope during long dry spells.

Written for you by our author Paul Arnold, edited by Sadie Harley, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you.

Publication details

Hao Bai et al, Unprecedented Amazonian rainforests damage during the 2023–2024 droughts, Proceedings of the National Academy of Sciences (2026). DOI: 10.1073/pnas.2514066123

Journal information: Proceedings of the National Academy of Sciences

Key concepts

effects of climate changedroughtsforest ecosystemslong-term ecological monitoring

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