The Amazon forest in the grip of a vicious circle of fires

A new study published by the Institute of Atmospheric Physics in China highlights an alarming phenomenon in the Amazon: the increase in fires, caused by climate change and deforestation.

Last year, Nasa warned that the atmosphere over the Amazon was drying up due to the increase of greenhouse gases and deforestation, causing an increase in the number of fires in the region. This time, it is a study conducted by the Institute of Atmospheric Physics (IAP) of the Chinese Academy of Sciences that renews this observation, while the Amazon forest has just experienced its worst year.

The atmosphere of the Amazon is drying up

I have never been to the Amazon rainforest,” says Gensuo Jia, one of the authors of the study published in the journal Global Change Biology. But I took a picture of it from my seat while flying over the Amazon during the 2018 fire season. It made my heart ache to think that so much greenery and freshness could have been reduced to ashes.” Climate change and deforestation are undeniably major factors in the increase in fires, but the interactions between these variables and the resulting processes are still poorly understood.

According to the work of Jia and colleagues, the combination of these two elements contributes to an increase in hot, dry days, while deforestation contributes to the drying of the atmosphere above the forest. The increased contribution of water vapour from the Pacific and Atlantic oceans also contributes to the increase in showers, but these are not enough to compensate for the long periods of intense drought. Indeed, because of deforestation and the drying of the canopy, precipitation circulates more freely once on the ground, forming channels instead of being absorbed and evapotranspired.

The urgency to stop the vicious circle

The southeastern region of the Amazon, characterized by savannahs that experience long dry periods, is the most exposed to the risk of repeated fires. Although the savannahs currently account for 90% of the fires in the Amazon basin, this does not mean that the rainforest is out of danger. Receding canopies and deforestation allow sunlight to reach and dry out the soil, which is covered with leaves, wood and organic compounds that together create the perfect mix for a fire to start.

As the years go by, the drought gradually intrudes and
and disrupts the rainy season and between seasons. And unfortunately, the more climate change and deforestation progress, the more the forest becomes locked in a loop that is bound to deteriorate.

“The increase in the proportion of area burned depends largely on the proportion of forest lost,” the researchers write. Thus, as the forest becomes more bare, more fires occur, denuding even more forest. “Promoting forest conservation and fire protection is crucial to safeguard the Amazon against further changes in climate and fire regime that compromise regional sustainability,” the team concludes.

Human activities are drying up the Amazon, Nasa warns

Every year, part of the Amazon forest burns. As spectacular as it is, this process is normal. Nevertheless, it is worsened by human activities… and the point of no return could be reached. Zoom on the weakness of the green lung of the planet: its water supply.

Last August, the whole world was moved for the Amazon, whose 7,853 km² went up in smoke during the first nine months of 2019. Compared to last year, Brazil, home to 60 percent of the Amazon rainforest, recorded an 84 percent increase in fire starts. And it is still burning in this month of November.

To understand this phenomenon, Nasa has analyzed data from the last 20 years. Its conclusions are clear: the atmosphere above the planet’s green lung has dried up considerably, making it more vulnerable to fires. The lead author of the study, Armineh Barkhordarian, from Nasa’s Jet Propulsion Laboratory, explains that more than half of this dryness is due to the increase in greenhouse gases, while the rest is caused by deforestation. The fragility of the Amazon is therefore entirely due to human activities.

The water evaporates, the forest dies

The largest tropical forest in the world, it remains a delicate ecosystem. Trees and plants absorb water through their roots, then release it as vapor through their leaves. The water can thus cool the air and lead to the formation of clouds so that the rain closes the cycle. By this operation, the Amazon generates 80% of the rain it needs.

When the air is dry and the temperature rises, the trees must transpire to cool down, but the soil no longer contains enough water to recharge their reserves. Vegetation dries up. Fire starts and grows more easily. Sassan Saatchi, co-author of the study, also a researcher at JPL, warns: “If this continues, the forest may not be able to feed itself” and the Amazon biodiversity will not survive.