As a diverse biome, the Amazon region turns into a home for a variety of "Amazons", with portions that differ from each other according to their own characteristics. Trees in the southern part of the Amazon ecosystem, for example, are more vulnerable to drought and, therefore, more likely to die. The conclusion is from a study signed by 80 researchers from Brazilian and foreign scientific institutions, including the Federal University of Western Pará (UFOPA), the State University of Mato Grosso, the University of Campinas and the University of Leeds, in the United Kingdom.
The increasing possibilities of drought in the Amazon, a region with an equatorial climate and heavy rainfall rates, result from human interference in the environment. Burning and deforestation provoke changes in soil configuration, as referred by Professor Everton Cristo de Almeida, one of the participants in the study from UFOPA. He recalls that the risks and consequences related to deforestation cannot be measured only by the deforested area, since the cutting of native trees causes the so-called "edge effect" – the deforested areas directly affect neighboring areas of standing forest, as they influence the water flow in- between plants, generating a deficit that increases the risk of drought.
"This accelerates conductance loss, that is, the transmission of water from the soil to the atmosphere. Plants are water pumps, transporting water from the soil through the xylem to the atmosphere. This process, known as Dixon's theory, promotes the passage of water through the plant and part of it is emitted into the atmosphere in the form of transpiration. When the plant undergoes water stress, the conductance decreases. And then we have xylem embolism – lack of water in the plant that will cease conductance – generating a loss of 50% of the water that reaches the leaves. In some cases, this deficit can reach up to 80%", says the researcher.
THREAT
But, if a few years ago, the possibility of streaks of drought extending across the Amazon seemed part of a dystopian future, today, the problem grows, continuously, affecting more and more locations, even outside the southern strip of the Amazon. According to Everton, the phenomenon is already noticed in the municipality of Nova Xavantina, in Mato Grosso, and in Caxiuanã National Forest, located in the municipality of Melgaço, in Pará. The study also included hotspots in Bolivia and Peru.
"In the south of Amazonas, the lack of water in the soil has caused accentuated mortality of plants. These long periods of drought are due to the advance of some development models that contribute to the loss of forest biomass", he evaluates.
With less water flowing amongst the trees, carbon sinks are also affected. Carbon sinks are places where the amounts of carbon absorbed are greater than the emissions. In the south of Pará and in the north of Mato Grosso, for example, the effect has been reversed, with both regions consolidating themselves as sources of carbon, with higher tree mortality. The forest is 30% drier and 2°C to 3°C warmer.
"The forest absorbs a lot of carbon, transfers it to the forest biomass and deposits it into the soil. All that plant material becomes a nutrient that will feed the forest. If there is a decrease in humidity of the areas, decomposition may be reduced and the incorporation of carbon into the soil is slowed down. It is a good example of the edge effect, because when deforestation takes place next to an intact forest region, that (deforested) area is (felt as) something unusual. So, the microclimate changes, the fauna feels it , seed dispersal changes and we have an increase in temperature, the rainfall cycle changes, the fauna begins to disappear, and we have harmful effects for small rivers and streams that permeate the Amazon Basin. The forest that is cut down directly impacts the standing forest" says Almeida.
Cutting-edge study included 500 tree samples
The research is based on sample collections of more than 500 trees in eleven sites in the Brazilian, Peruvian and Bolivian Amazon between 2014 and 2018. The researchers measured the physiological characteristics of the trees and analyzed the level of water stress of the plants. Researcher Julia Tavares, from the University of Uppsala, Sweden – lead author of the article – believes that the study's conclusions may contribute to the conservation of regions of the Amazon that are more susceptible to extreme weather events.
"In order to understand large-scale spatial and temporal patterns in the Amazon, given its magnitude and heterogeneity, an enormous collaborative effort by the scientific community is essential. Furthermore, all this ecophysiology work requires detailed measurements, with collections being carried out during the early hours of the morning and samples taken from the top of the trees, which are between 30 and 40 meters high. In order to understand the nuances in the responses of different Amazonian forests to the ongoing and future climate changes, it is essential to invest resources in order to carry out research and value national researchers”, says Julia in an interview with the Bori agency.
Levels of Amazon rivers have been affected
Droughts caused by growing deforestation and wildfires do not affect only trees. The rivers in the Amazon region have faced twelve consecutive years with below-average water levels. The scenario was finally reversed in 2022, with the help of the La Niña phenomenon. According to data released by the MapBiomas Água platform, the Amazon region presented a water surface of 11.3 million hectares last year, 13% above 2021. However, the historical drought record in the region is worrisome. Between 1985 and 2022, the region experienced 23 years with below-average water surface, 14 years above average, and only one year at the average level. The worst drought scenario occurred between 2016 and 2021, when the water surface varied from 8% to 4% below the average. There are many examples in recent years: the worst drought event in the history of the Amazonas State was recorded in 2010. At that time, the water level of the Negro River in the capital Manaus reached only 13.63 meters. To put it into perspective, during the flood season, the river can reach 29 meters. The Acre and Solimões rivers also experienced historic droughts in 2022.
Droughts also affect Brazilian regions far from the Amazon. Professor Henrique Barbosa from the Institute of Physics, at the University of São Paulo, published a paper showing how Amazonian humidity and its transformation into rain in the South and Southeast of Brazil is calculated. The research demonstrated, for the first time, that the direct transport along with the secondary transport of humidity from the Amazon accounts for 27% of the rainfall in these two Brazilian regions. In other words, if there is a loss of vegetation cover in the Amazon, there will be less rainfall in other regions of the country.
Adaptation potential has decreased
Researcher Monique Rodrigues, from the National Center for Monitoring and Alerts on Natural Disasters, highlights that the states of Pará and Amazonas experience a seasonal reduction in rainfall that typically occurs after the month of June and can last until November. In the northern region of Mato Grosso, precipitation rates remain below 100 mm between the months of April and September, and it can even reach an average monthly precipitation of 0 mm. This seasonal pattern of precipitation generally elicits a response from vegetation adapted to this environment, particularly in the transition zones between cerrado and dense forest within the Amazon biome.
However, due to the extreme droughts, this adaptation is not sufficient during certain periods, leading to the mortality of the taller trees and specimens in areas with higher biomass stocks in vegetation, such as in the eastern region of the Amazon Basin. Rodrigues emphasizes that these areas are the ones close to roads and easily accessible locations, as well as those with mining activities and land leasing for monocultures and livestock production.
"Due to the increase in deforestation of the regions' native biomes, evapotranspiration is reduced, climate extremes increase, and we have environments and people becoming less and less resilient and adapted to these contexts. Drought season lasts long during the natural climate cycle that can occur anywhere in the world. However, when it becomes more recurrent, intense and prolonged, the most sensitive species can suffer the impacts of the unavailability of water. This fact generates mortality in the most sensitive tissues and cells of gas exchange and in the osmotic balance in plant species cells", she points out.
More severe consequences are avoidable
Researcher at the National Center for Monitoring and Alerts on Natural Disasters, Monique Rodrigues believes that the way to prevent the threat of drought is to guarantee the execution of nature-based project solutions, focusing on preservation and restoration where deforestation occurs. She lists some alternatives: investing in remote monitoring, classifying and evaluating the occupation and use dynamics of each region and, finally, identifying actors responsible for the areas to engage them in the reversal of processes that cause extreme climate effects.
"(It is important) to identify young people in the region, vulnerable and low-income people who will be qualified and trained to implement the solutions. Other activities such as installation of new nurseries, collection of seeds, marking of matrix trees with GPS and identification by geospatial technology, preparation of seedlings, preparation of compounds such as black soil, commercialization of products from local biodiversity and bioeconomy. There are often structured cooperatives that do not have legal status. There are also teams of volunteer brigade members who already have a structure for collecting seeds and creating seeds nurseries, but don't have the resources to maintain the activity periodically", she reports. According to the researcher, ways of financing these projects may be via the federal government or voluntary carbon credit markets, as well as investors from the private sectors via tax reduction or socio-environmental responsibility of companies.
