Amazon’s Changing Climate: Insights from Tree Growth Rings
The rainfall patterns in the Amazon have undergone significant changes, sparking concerns about the overall drying of the region. Recent studies leveraging dendrochronology—examining tree growth rings—reveal an increasing intensity in seasonal rainfall variations over the past four decades.
In 2024, the Amazon Basin experienced a drought of historic proportions, affecting water levels across the region. Manaus, the largest city on the Amazon River, recorded its lowest water level since 1902, while high temperatures in Lake Tefé led to the death of river dolphins in 2023. These consecutive droughts have prompted scientists to explore whether these events signify a broader drying trend due to intensified El Niño and La Niña cycles, alongside deforestation impacts.
Researchers from the UK and Brazil’s National Institute for Amazonian Research have turned to the trees themselves for answers. By analyzing growth rings, they have reconstructed past climate conditions, revealing a complex picture of shifting rainfall patterns.
Their study indicates an unprecedented change in the Amazon’s hydrological cycle. Over the last 40 years, wet seasons have become wetter, with rainfall increasing by 15-22%, while dry seasons have grown more arid, with a 5.8-13.5% decrease in precipitation.
Understanding the Intensifying Extremes
Lead author Bruno Cintra from the University of Birmingham highlights the study’s focus on the seasonal variability observed in different forest types. Samples were collected from floodplain forests and dryland areas, revealing the impacts of these changes on the trees’ growth.
“The idea for our paper comes from a long-standing question, which is to understand what is happening to the Amazon’s climate through a data set with large-scale spatial representativeness and a good time range,” Cintra explains.
Co-author Jochen Schöngart of INPA notes that the most extreme floods and droughts in the central Amazon have occurred in recent years, supporting the study’s findings. “The four most intense floods in the history of the central Amazon — in 2021, followed by 2012, 2009 and 2022 – occurred during the last 16 years,” he said. “In parallel, the three most intense hydrological droughts in the region took place in 2024, 2023 and 2010, respectively.”
These patterns suggest a climate hub characterized by a wetter wet season in the north and a prolonged dry season in the south, with central areas experiencing both extremes.
Rethinking Tropics’ Tree Growth
Historically, the scientific community believed tropical trees lacked distinct growth rings due to stable temperatures. However, recent studies have debunked this myth, showing that tropical trees do form rings in response to seasonal changes in water availability.
Peter Groenendijk, a professor at the State University of Campinas, emphasizes the importance of these findings. “This belief that tropical trees do not form growth rings has been published in every biology textbook around the world,” he remarks. “But, after the myth started to dissolve in the early 2000s, dendrochronology in the tropics began to grow.”
Groenendijk’s work with the Tropical Tree-Ring Network has expanded our understanding of how droughts and climate change affect tree growth in tropical regions.
The insights from these studies underscore the intricate interplay between natural variability and human activities, such as deforestation, in shaping the Amazon’s climate. As scientists continue to unravel these complexities, the role of tree growth rings in climate research becomes increasingly indispensable.
Original Story at news.mongabay.com