"Even untouched forests are burning"

Max Planck researchers are witnessing first-hand the alarming scale of forest fires in the Amazon

Deforestation and subsequent fragmentation have made vast areas of the rainforest more susceptible to fires, as demonstrated by the current situation. The ongoing deforestation also intensifies drought conditions, a problem that is particularly severe during El Niño years. This appears to be a key trigger behind the extreme conditions seen today. In September and October 2023, scientists from the Max Planck Institutes for Biogeochemistry and Chemistry conducted a measurement campaign at the Amazon Tall Tower Observatory (ATTO), located deep within the rainforest. During this campaign, they directly observed the escalating effects of the current El Niño.  
 

The researchers have now analysed two major El Niño events—2015/16 and 2023/24—using data from the ATTO measurement station. These intense events typically span two consecutive years and are closely linked to severe droughts in the Central Amazon. The year 2024 has already started with unusually dry conditions, contributing to an especially intense fire season. The number of fires recorded in July and August was significantly higher than in previous years, and the peak fire month of September is also expected to surpass last year's figures.

Already last year, conditions in the Amazon were extremely critical during the dry season. A lack of rainfall led to severe drought, causing water levels in rivers throughout the Amazon basin to drop dramatically. Equally concerning were the fires and the dense smoke they generated. "We recorded unprecedented levels of soot and carbon monoxide in the atmosphere at our station," reports Sebastian Brill, a researcher at the Max Planck Institute for Chemistry who studies atmospheric pollution from tiny aerosol particles. The reason for this was the many fires throughout the Amazon basin and in the region around the Amazon River itself, particularly around Santarém. "What was especially alarming," Brill notes, "was that such severe fires occurred even in areas of largely untouched primary forest."

Fragmentation increases fire risk

The so-called primary forest, which is typically resistant to drought and fire, is becoming increasingly fragmented due to ongoing deforestation in the Amazon. This fragmentation creates more exposed edges, which dry out faster, making these areas more vulnerable to drought and fire. The El Niño-induced drought of 2023 further amplified this effect Fires intentionally set in deforested regions were able to spread into untouched rainforest, burning through the undergrowth and destroying the vegetation. This process further weakens the forest, making it even more susceptible to future fires and increasing the likelihood of large-scale fires in the same areas in subsequent years.  

The forest remains under significant stress from last year’s pollution. In addition, the soil is drier than usual and the river levels are low. As a result, just like in 2023, fires originating in deforested areas are increasingly spreading into neighbouring primary forest, destroying huge areas. "In 2023, the forest was so dry in some places that even areas of rainforest without prior deforestation were able to catch fire," explains Sebastian Brill. "Fires set in deforested regions spread were able to spread into untouched rainforest, leading to its destruction."

Rainforest's carbon storage capacity declines

In a study published in advance by the Max Planck Institute for Biogeochemistry, the researchers demonstrated that the 2023 drought significantly reduced the Amazon's capacity to store carbon. Simultaneously, fires in the savannah regions released more carbon dioxide than the rainforest could absorb. The researchers predict that the Amazon rainforest’s carbon storage capacity will decline even further this year.

The stability of the Amazon ecosystem relies on a complex water cycle that has a significant impact on most of South America. The fragmentation of the forest through deforestation prevents water from evaporating efficiently, resulting in less water being released into the atmosphere. This leads to fewer clouds forming and reduced water transport to other regions.  Furthermore, smoke from fires disrupts cloud dynamics and, in extreme cases, can entirely suppress cloud and rain formation. The evaporation and transport of water vapour, often referred to as ‘flying rivers’, play a central role in South America's climate. They are crucial for maintaining ecosystem stability and ensuring the survival of the Amazon rainforest.