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Two consecutive droughts, each more intense than previous ones experienced by Amazonian forests in the year 2023-2024, have altered their ecological function, forest moisture and biomass to the lowest in more than three decades, a new study has found.
The research team said the satellite radar findings during the 33-year period from 1992 until 2025 assessed by them reflected a worrying trend that record-breaking droughts pushed moisture and biomass to its lowest.
Amazonian rainforests are one of the planet’s most crucial carbon reservoirs and biodiversity hotspots, storing nearly a quarter — 17 to 23 per cent of global forest carbon stocks.
“Model projections indicate that the post-drought recovery of the 2023-2024 event will likely be the lowest of all major droughts recorded since 1992. These findings provide an assessment of the impacts of the most recent droughts for Amazonian rainforests and highlight their growing vulnerability to intensifying climate extremes,” the paper said.
Published in the journal PNAS, the study analysed other mega-droughts including those in 1997-1998, 2005, 2010, and 2015-2016.
It found that nearly 26.8 per cent of forests reached their lowest moisture and biomass levels in over three decades, a ratio more than double witnessed during the major drought of 2005 that was documented to be 11 per cent.
The sharpest and most widespread declines were observed in the eastern regions of the Amazon.
This finding is alarming, as tropical intact forests in South America have already suffered a 17 per cent decline in carbon stock and a 42 per cent reduction in sink since the 1990s, driven by deforestation and drought-induced tree mortality under intensifying anthropogenic climate change, the study underlined.
The modelling results from the investigation indicated that 53.7 per cent of intact Amazonian forests are unlikely to recover to pre-drought conditions before the seventh post-drought year. “Our results indicate that the 2023-2024 droughts may have caused the most severe canopy moisture decline and aboveground biomass loss in the past three decades, leading to substantial reductions in carbon stocks and weakening of the intact forest carbon sink, with limited prospects for full recovery in 7 years,” it noted.
The study observed that only 46.3 per cent of intact Amazonian rainforests could return to pre-drought conditions, with uncertainty ranging from 32.3 to 61.1 per cent, it said.
The estimated recovered ratio—46.3 per cent—was the lowest among all the past major droughts, compared to 56.5 per cent for 1997-1998, 56.1 per cent for 2005, 70.6 per cent for 2010, and 57.3 per cent for 2015-2016 droughts. The findings highlight that the 2023-2024 droughts will likely have a long-term impact on Amazonian forests, the authors said.
According to the paper, water availability plays a crucial role in recovery of these forests. “Cumulative water excess was a more important predictor than drought severity and other biophysical variables, emphasising the critical role of post-drought water availability in recovery,” the study said.
Citing an instance from the 2010 drought, the study found that the fastest recovery was followed by favourable moisture conditions. Besides, forests likely to recover up to seven years post the 2023-24 droughts are likely to grow on soils with lower fertility and higher sand content compared to those that could not recover, suggesting a change in functioning towards building resilience.
Limited soil fertility may lead trees to allocate more resources toward drought-tolerant traits such as denser wood and higher xylem embolism resistance, whereas more-fertile soils typically support fast-growing species with higher turnover rates, which are more vulnerable to drought stress, the study said.
It added, “In terms of soil texture, sandy soils are coarser and less compact than clay soils, making them slower to reach the wilting point, thereby enhancing water availability in shallow-water- table forests widely distributed across the Amazonia. Forests projected to recover within 7 years also exhibited lower canopy heights, consistent with the fact that taller trees are more susceptible to drought-induced mortality due to increased hydraulic risk.”
The researchers warned that given that the severe droughts in the Amazon have repeated about every seven years during the studied period, the rainforests may witness another drought spell pushing them to extremes before allowing them to recover completely from the 2023-24 event.
Although long-term drought experiments suggest that Amazonian rainforests may eventually reach ecohydrological stability, their ecosystem structure changes significantly, leading to reduced biomass and woody carbon accumulation. Consequently, future intensifying droughts may drive continued declines in canopy moisture and aboveground, the study said.
The authors said the findings highlight the growing vulnerability of Amazonian rainforests to intensifying climate extremes driven by El Niño events, and human-driven climate change. They said it indicated that forests are approaching their thresholds of their preindustrial operating space.
The study comes in the backdrop of a ‘Super El Niño’ predicted to form in the coming months. This would again allow less time to recover from the previous drought.