In a super-preserved part of the Brazilian Amazon, in a central area of the biome, the extreme drought of 2023 was felt in an impressive way — a word used by scientists who monitor indicators, dynamics and behaviors of a still healthy forest.
The crisis in the second half of last year — it was the worst drought in history, taking into account measurements of river levels in the western Amazon — put pressure on even areas of preserved forest, which are not influenced by deforestation, urban occupations and predatory activities.
The level of stress in the biome, which feeds the central concern about the Amazon becoming more of a source than a sink of CO2, was captured in exact measurements by Atto (an acronym in English for Observatório da Torre Alta da Amazônia), a scientific project resulting from partnership between Brazil and Germany that uses 80-meter and 325-meter towers to measure the Amazon atmosphere.
Tall tower in the middle of the Amazon rainforest
Atto already has enough data to compare what has happened in the forest, in an area of the central Amazon, over the last ten years. Folha obtained this data.
The average maximum air temperature in September at a height of 81 meters (above the tree canopy) was 35.98°C. Atto sensors captured averages of 38°C at the height of the crisis, at a height of 40 meters.
September and October were the peak months of the extreme drought, which isolated riverside and indigenous communities, made rivers and streams disappear, displaced groups and increased fires and waves of smoke.
Air humidity, taking into account the average minimum values in September, also at a height of 81 meters, reached 20.14%. The ground heated up, with maximum temperatures reaching almost 28°C.
Taking into account the measurements made by scientists over the last ten years, from 2014 to 2023, all these values are extreme, the peaks recorded for the month of September in the area where the towers are installed.
The closest reality to what happened in 2023 was that of 2015, when there was also an incidence of the effects of an El Niño, a climate phenomenon that consists of above-average warming in the Pacific Ocean, close to the Equator. El Niño impacts temperature and rainfall.
The stress experienced by the forest in 2023 was slightly worse than that experienced in 2015, according to Atto measurements.
Extreme drought of 2023 was measured in numbers, in a preserved point in the center of the Amazon, the Uatumã reserve, 150 km from Manaus
“With these temperatures [na altura ou acima da copa das árvores], the sheet does not work well. The tree sweats, and the level of evapotranspiration is very high”, says Cléo Quaresma Júnior, professor at the Federal Institute of Pará and researcher at Atto responsible for micrometeorological measurements.
“There is a loss in the ability to remove CO2 from the atmosphere. And the emission continues, the plant is breathing all the time”, says Quaresma.
Researcher Hella van Asperen, who takes care of greenhouse gas concentration measurements at Atto, states that the effects of El Niño are still present.
“The forest hasn’t had time to recover, and it’s raining less. It’s going to be a difficult year”, says Asperen, who works in Amazonas. She is also a postdoctoral researcher at the Max Planck Institute for Biogeochemistry in Germany.
Atto’s towers and equipment are installed in the Uatumã RDS (Sustainable Development Reserve), in Amazonas, 150 km from Manaus. It is a central area of the Amazon and can be understood as part of the western Amazon, where the extreme drought of 2023 had the most severe effects.
Measurements have been made since 2012, using various sensors. The existing towers are within a 20 km radius of the reserve.
Scientists seek more accurate understandings of the exchanges between the forest and the atmosphere. To do this, measurements are taken every half hour, daily. One of the project partners is Inpa (National Amazon Research Institute), based in Manaus.
This is how Atto describes why it conducts research on these exchanges: “The Amazon is responsible for a large part of the world’s photosynthesis, stores billions of tons of carbon and moves large amounts of water. However, we are still far from understanding the role of the Amazon in an Earth system in transition.”
Minimum air humidity levels approaching 30% — or reaching just over 20%, as in September, at a height of 81 meters — are considered impressive for the Amazon rainforest, in the perception of the scientists involved.
These researchers still do not have an answer about the possibility of the reserve where the towers are located becoming predominantly a source of carbon emissions in drought, and not a sink. They hope to have more concrete data on this in the coming months.
In 2015, this flow approached zero, but still had a slight advantage in CO2 absorption, according to Atto members.
“Some parts of the Amazon are emitters, especially parts closer to agricultural frontiers, such as southern Pará and northern Mato Grosso,” says Quaresma. “In the years following the 2015 El Niño, the forest absorbed a lot of CO2, but it needs time to regenerate. And the dry periods are getting longer and longer.”
Measurements on the concentration of greenhouse gases show an increase over the years in both carbon monoxide (CO), associated with fires, and carbon dioxide (CO2).
There were days when clouds of smoke covered part of the reserve, in the same way as happened with Manaus. In the most populous capital of the Amazon, with 2 million residents, there were consecutive days of smoke, with repetitions for months, during the 2023 drought.
The measurement of carbon monoxide in the forest area showed, at one point, levels similar to being positioned “behind a truck”, according to Asperen. The concentration of gases does not only concern the dynamics of the forest, but various emissions, which also reflect on points of native vegetation.
El Niño was one of the causes of the extreme drought in 2023. Other factors were the effects of climate change, already felt in the Amazon, forest degradation in different parts, and the warming of the North Tropical Atlantic.
Rivers that are decisive for Amazonian life have reached historic lows. The Negro River, in Manaus, reached 12.7 meters in October, the lowest level in 121 years of measurements in the city’s port. Taking into account the lows in previous years, the worst measurement had been recorded in October 2010: 13.63 meters, almost one meter more than the current worst mark.
The extension of the drought, with a change in the rhythm of the current rainy season, leaves doubts about the behavior of the drought in 2024, a period that begins in June. Researchers believe in the possibility of another year with severe drought.
The information is from the Folha de São Paulo newspaper.
Tags: Research proved extreme drought minimum humidity maximum temperature Amazon
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