Worst Drought Ever in the Amazon, Caused By Climate Change

The fifth, 100-year drought since 2005 has struck the Amazon in 2023; this one more extreme than any of the previous events. Each of these droughts except one were more extreme than the previous. These were 2010, 2015/2016, the smaller one in 2020, and the current in 2023-2024. As another possible sign of worsening climate change conditions, this one started in the pre-rainy season, where the others started in the rainy season.

The World Weather Attribution Network published on January 24, 2024 that, “the likelihood of the meteorological drought occurring has increased by a factor of 10, while the agricultural drought has become about 30 times more likely.” A meteorological drought occurs when precipitation falls below a certain threshold. An agricultural drought combines precipitation with timing of the precipitation and exasperation of the drought from excessive heat.

Prior to the current 2023 drought, that is ongoing and expected to worsen further because of our current El Nino, the Amazon has been influenced by droughts that each increased in extremeness from the previous to a rarity beyond the 100-year event in the years: 2005, 2010 (Lewis 2010 and here), (Erfanian 2017), (Yang 2018) 2016 (Feldpausch 2016). All three of these increasingly severe droughts created forest mortality flipping the Amazon to emissions instead of sequestration. The rapid cycling of organic material in tropical forests then likely reversed this flip before the next drought pulse arrived. Warnings after the 2010 drought, that repeated droughts such as these could flip the Amazon permanently, have now been amplified by the Super El Nino drought of 2016 and subsequent drying from continued warming. Current findings (Qin 2021, and Gatti 2021) show the Amazon is emitting between 1 Gt and 2.45 Gt CO2eq annually, based on averages from 2010 through 2018 and 2010 through 2019. Now we have the most extreme drought yet in the Amazon.

Caused by climate change, not human deforestation… Deforestation is responsible for about a quarter of the emissions from the Amazon. Forest mortality from drought and degradation from climate change-caused fire and water stress is responsible for the remaining 75 percent (Qin 2021). It is also important to note these quantities of emissions are averages and the degradation is very likely increasing in extremeness, making the 1 Gt and 2.45 Gt CO2eq quantities understated.

Controversy? … In 2022, Boulton, Lenton and Boers published work in Nature Climate Change that showed the Amazon was nearing a critical transition based on loss of resilience of three-quarters of the Amazon since 2000, with a risk of “profound dieback”. From Nature Climate Change, “We find that more than three-quarters of the Amazon rainforest has been losing resilience since the early 2000s, consistent with the approach to a critical transition. Resilience is being lost faster in regions with less rainfall and in parts of the rainforest that are closer to human activity. We provide direct empirical evidence that the Amazon rainforest is losing resilience, risking dieback with profound implications for biodiversity, carbon storage and climate change at a global scale.”

A conflicting paper was published by Tao et al., in 2023 that questioned three of the metrics used by Boulton 2022. The resulting rebuttals revealed weakness in the questioning of Tao 2023,and then very meaningfully, as if to roundly assert Mother Nature’s fury, the worst drought yet in Amazonia occured in 2023.

More publishing on the flip… To add an exclamation to this apparently obvious trend, Bochow and Boers published findings in Science Advances that show their modelling reveals a transition to substantially drier conditions is underway because of increasing drought, fire and land use change. They state that this transition would lead to conditions where the rainforest could likely not be maintained. It is important to note that Boxhow and Boers’ work only extends through 2019 and does not include the 2020 and 2023 drought pulses. Abstract, “The Amazon rainforest is threatened by land-use change and increasing drought and fire frequency.  Studies suggest an abrupt dieback of large parts of the rainforest after partial forest loss, but the critical threshold, underlying mechanisms, and possible impacts of forest degradation on the monsoon circulation remains uncertain. Here, we use a nonlinear dynamical model of the moisture transport and recycling across the Amazon to identify several precursor signals for a critical transition in the coupled atmosphere-vegetation dynamics. Guided by our simulations, we reveal both statistical and physical precursor signals of an approaching critical transitionin re-analysis and observational data. In accordance with our model results, we attribute these characteristic precursor signals to the nearing of a critical transition of the coupled Amazon atmosphere-vegetation system induced by forest loss due to deforestation, droughts, and fires. The transition would lead to substantially drier conditions, under which the rainforest could likely not be maintained.”

REFERENCES (not linked above)

Conflict over Amazon tipping point… Tao 2023, questions Boulton 2022’s pronounced loss of forest resilience over Amazonia since 2003, and Boulton Challenges Tao. Toa suggests the Amazon is not nearing a transition because of the vegetation optical depth (VOD) they used in their analysis and contamination from soil moisture and sensor discontinuity over Amazonia. Tao 2023 uses an independent radar dataset to show that the decreasing trend in forest resilience is at best limited, and has been partly reversed in recent years, thus challenging the conclusion that Amazonian rainforests are approaching a tipping point.
Tao et al., Little evidence that Amazonian rainforests are approaching a tipping point, Mature Climate Change, November 9, 2023.
Researchgate free account required) https://www.researchgate.net/profile/Jean_Pierre_Wigneron/publication/375523532_Little_evidence_that_Amazonian_rainforests_are_approaching_a_tipping_point/links/654f812b3fa26f66f4f466cd/Little-evidence-that-Amazonian-rainforests-are-approaching-a-tipping-point.pdf?_tp=eyJjb250ZXh0Ijp7ImZpcnN0UGFnZSI6InB1YmxpY2F0aW9uIiwicGFnZSI6InB1YmxpY2F0aW9uRG93bmxvYWQiLCJwcmV2aW91c1BhZ2UiOiJwdWJsaWNhdGlvbiJ9fQ

Boulton 2023 response –
Flooding:  “Changes occurred after the anomalies had already started to develop… At first glance, there are indeed strong positive VOD anomalies close to 2009 and 2012 (Fig. 1a). However, the VOD anomaly is high already a year before the flood onset in 2009, and the flood of 2012 ends before the corresponding VOD anomaly. Moreover, large floods in the Amazon basin also occurred in the years 1999 and 2014, which do not appear in the VOD time series.”
Sensor discontinuity: Boulton2023 Reply to Tao 2023 included a single sensor evaluation for July 2002–June 2011 (to obtain complete months and years), using a five-year moving window as before. Due to the overall shorter time span of AMSR-E, we also show results using a three-year window; this does not qualitatively change the results.”
Reply to: Little evidence that Amazonian rainforests are approaching a tipping point, Nature Climate Change, November 9, 2023.
https://www.researchgate.net/publication/375523505_Reply_to_Little_evidence_that_Amazonian_rainforests_are_approaching_a_tipping_point

Boulton 2022…  “We find that more than three-quarters of the Amazon rainforest has been losing resilience since the early 2000s, consistent with the approach to a critical transition. Resilience is being lost faster in regions with less rainfall and in parts of the rainforest that are closer to human activity. We provide direct empirical evidence that the Amazon rainforest is losing resilience, risking dieback with profound implications for biodiversity, carbon storage and climate change at a global scale.”
Boulton, Lenton and Boers, Pronounced loss of Amazon rainforest resilience since the early 2000s, Nature Climate Change, March 7, 2022.
https://www.nature.com/articles/s41558-022-01287-8

South American Monsoon Tipping activated… 
Bochow and Boers, The South American monsoon approaches a critical transition in response to deforestation, Science Advances, October 4, 2023.
https://www.science.org/doi/epdf/10.1126/sciadv.add9973

Worst 100-year Amazon Drought in 2023 UN Sustainable Solutions Network…
Costa and Morengo, Statement on the 2023 Amazon Drought and Its Unforeseen Consequences, United Nations Sustainable Solutions Network, December 7, 2023.
https://www.theamazonwewant.org/wp-content/uploads/2023/12/231207-AMAZON-DROUGHT-STATEMENT_ENGLISH.pdf

Amazon Collapse from Climate Change, Not El Nino…
World Weather Attribution, January 24, 2024.
(Summary) ‘https://www.worldweatherattribution.org/climate-change-not-el-nino-main-driver-of-exceptional-drought-in-highly-vulnerable-amazon-river-basin/
(Full) Climate change, not El Niño, main driver of exceptional drought in highly vulnerable Amazon River Basin, World Weather Attribution network, Imperial College of London, January 24, 2024.
https://mcusercontent.com/854a9a3e09405d4ab19a4a9d5/files/656e65ee-3426-f756-195d-ea5678adc1bb/WWA_scientific_report_Amazon_drought.pdf