Research shows Amazon drought could have long-lasting effects on global carbon cycle

The extreme El Niño conditions of 2015-2016 caused a significant loss of carbon that was locked away in the Amazon basin. Now it has been shown that these effects may be longer lasting in the carbon cycle.

Amazon drought
During the El Niño periods, general circulation tends to develop droughts over the Amazon basin. Image: Greenpeace.

One of the most intense El Niño events of the last decades is the one that occurred between 2015 and 2016. It was in that case that the Amazon basin was seriously affected by the drought that hit that ecosystem. As Eos indicates, on that occasion the surface vegetation was severely reduced and caused the basin to release almost 1 gigatonne of carbon into the atmosphere.

The effects of the drought in the Amazon generated by the intense El Niño of 2015-2016 generated a release into the atmosphere that has not been recovered over the years.

Now, a recent research published in Advances Space and Earth Science found that although surface biomass took more than a year to recover, the recovery of total carbon loss, including underground biomass and soil carbon, took much longer. The working group was led by Junjie Liu of NASA's Jet Propulsion Laborator and the California Institute of Technology.

Total carbon reserves throughout the basin had not yet returned to pre-drought levels at the end of 2018. The study examined three different areas of the Amazon: the northeast, the tropical rainforest of the west-southwest and the dry savannah of the southeast. The researchers used nine years of monthly satellite data on gross primary production, fire emissions and net biosphere exchange to examine how drought-induced atmospheric and soil drought affected carbon flows.

Drought and loss of carbon reserves

According to the results of this research, the northeastern Amazon, the region most affected by drought, still faced a cumulative loss of 0.6 gigatons of carbon until December 2018 as a result of El Niño of 2015-2016. The deficit was mainly due to the reduction of photosynthesis, and the consequent absorption of carbon by vegetation subjected to water stress.

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In the southeastern savannah, the loss of carbon was partly due to the fires. And in the west-southwest, the loss of water may have affected the plants. It is common for carbon absorption to decrease in response to atmospheric dryness and lack of groundwater, but researchers found that carbon absorption decreased three times more than expected.

Specialists also showed that as long as the drought persists in the Amazon, the crucial processes of the carbon cycle may continue to be affected by rising temperatures, arid conditions and water storage deficits. Until now, most of the account continues under rain below average.

Impacts of El Niño on a large scale

The summary of the study indicates that the link between the impact of drought and the recovery of total carbon deposits and their biogeochemical drivers is still unknown. It was also shown that the attenuation of carbon absorption is three times greater than expected from the pre-drought sensitivity to atmospheric aridity and groundwater supply.

Amazon river drought
The drought in the Amazon has seriously compromised the main economic resource of the region, which is the rivers that make up the basin. Image: Greenpeace.

The results suggest that the disproportionate impact of water supply and demand could compromise the resilience of the Amazon carbon balance to future increases in extreme events. Specifically, what is observed is that the drought process has allowed a great loss of carbon that was sheltered in the vegetation and demonstrates how a phenomenon can feed back others in the atmosphere.

The future durability of this carbon reservoir is very uncertain, which contributes significantly to the uncertainties of the predictions of the global carbon cycle. It is expected that the soil and the underlying atmosphere of the tropical region of South America will become drier in the future, so it is essential that it is understood how the carbon cycle will respond to this combined atmospheric and soil drought.

Reference of the news:
Liu, J., Bowman, K., Palmer, P. I., Joiner, J., Levine, P., Bloom, A. A., et al. (2024). Enhanced carbon flux response to atmospheric aridity and water storage deficit during the 2015–2016 El Niño compromised carbon balance recovery in tropical South America. AGU Advances, 5, e2024AV001187.https://doi.org/10.1029/2024AV001187