outubro, 17 2023

By Fábio de Castro, special for WWF-Brazil

In mid-2021, above-normal rainfall led the Negro River - one of the most important in the Amazon - to surpass the highest level ever measured in 120 years, flooding entire cities for months, with serious social and economic consequences. Now, the Amazon is experiencing an extreme drought that has reduced the flow of its main rivers, causing equally serious problems. Just over two years after those historic floods, the level of the Rio Negro reached 13.59 meters in Manaus this Monday, October 16, the lowest since 1902.

For science, this radical contrast in a short period indicates that the Amazon is already feeling the effects of the climate crisis that the Intergovernmental Panel on Climate Change (IPCC) has been warning about for several years: an increasingly frequent alternation of extreme events - whether from droughts or severe floods.
This scenario of rapid alternation between extremes is the result of complex processes linked to climate change that affect several parts of the world, but, in the Amazon, their local effects are exacerbated by deforestation and wildfires.

Experts who study the ecology and hydrology of the biome fear that the interaction between all these factors will produce an imbalance that could lead the world's largest tropical forest - or at least vast parts of it - to a tipping point from which the rivers and biodiversity are no longer able to recover.

"The combination of climate change and rampant deforestation contributes to the worsening and prolongation of the drought, which, in turn, leads to an increase in fires, which tends to further exacerbate the effects of drought, affecting the rainfall regime. This impacts not only in the lives of local people, but also affects the economy and water security of other regions, as what happens in the Amazon interferes with other biomes”, says Edegar de Oliveira, director of Conservation and Restoration at WWF-Brazil.

For researcher Jochen Schöngart, from the National Institute for Amazon Research (Inpa), it is necessary to be careful when talking about a tipping point, because the Amazon is very heterogeneous and has regions that are more vulnerable than others. “However, some regions are already experiencing processes that make them very susceptible to collapse, such as the Southern Amazon, where the synergy between climate change, deforestation and large-scale wildfires are worsening and expanding the dry season,” he says.

According to him, studies led by climatologist José Marengo, from the National Center for Natural Disaster Monitoring and Alerts (Cemaden), show that, in the last 50 years, the dry season has already increased by at least one month in the South of the Amazon. “If the temperature of the Tropical Northern Atlantic Ocean continues to increase, with fires and deforestation at the current rate, we will reach a point where even human populations will have difficulty living in this region,” he says.

Although it represents serious risks for the southern region of the biome, the extreme drought of 2023 is causing more serious problems in the Western Amazon, which comprises the states of Acre, Rondônia, Roraima and Amazonas, and already affects more than 500 thousand people.

Important rivers such as the Negro, the Solimões, the Purus, the Madeira and the Amazon are heading towards their lowest levels in history, while entire cities, which can only be accessed by rivers, are at risk of becoming isolated. In several locations, rivers are already impassable, making it impossible to transport food and medicine and to supply water.
 

Broad impacts

According to Schöngart, a combination of climatic factors makes the current drought different from previous ones and has impacts on practically the entire Amazon territory. According to him, this year's drought is caused, on the one hand, by an El Niño of the EP (Eastern Pacific) type, which warms the waters of the Pacific Ocean off the coast of South America. “This kind of El Niño has impacts of greater magnitude over the centre, north and east of the Amazon, expanding a little towards the southeast”, he states.

On the other hand, the warming of the North Tropical Atlantic, resulting from climate change, mainly affects the south and southwest regions of the biome. “The synergy between the two phenomena intensifies the drought in practically the entire Amazon region, increasing temperatures and reducing cloud cover, resulting in surface warming”, explains the researcher.

With the warming of the North Tropical Atlantic, the Intertropical Convergence Zone - a band of clouds that circles the entire globe in the equatorial region - is positioned further north and, as a result, water vapour generated on the surface of the Atlantic is transported to higher latitude regions, instead of reaching the Amazon. According to Schöngart, the effects this year are even stronger because we are in a warm phase of the Atlantic Multidecadal Oscillation, which happens every three or four decades.

“These oscillations are natural, but there is also evidence of human influence in this warming process in the North Atlantic. With greenhouse gas emissions, the Southern Hemisphere wind belt has migrated more towards Antarctica in recent decades, which is probably related to the hole in the ozone layer on that continent and the increase in greenhouse gas concentrations in the atmosphere. With this change, warm surface waters from the Indian Ocean end up passing around South Africa and invading the Atlantic. These waters contribute to the warming of surface waters of the tropical region of the ocean,” he explained.

The combination of all these factors produced a brutal reduction in precipitation in the Amazon this year, transforming the meteorological drought - characterised by a lack of rain - into a hydrological drought, which is reflected in low water levels in rivers, with serious impacts on biodiversity. 

“That's why we're seeing images in the press of deaths of riven dolphins, arapaima and manatees. The volume of water becomes smaller, causing it to heat up quickly. The impact of this phenomenon is particularly serious for riverside populations, who are isolated and have difficulty obtaining essential services such as water supply, food, health and education. Many municipalities are already without access, as boats don’t arrive,” he says.

Since September 23, with the drought spreading strongly across the Amazon and water temperatures rising, 153 river dolphins have been found dead in the region: 130 pink and 23 of the tucuxi species, according to the Mamirauá Institute for Sustainable Development (IDSM). Only on the 28th, when the water temperature reached 39.1°C, 70 river dolphin carcasses were recorded, in addition to hundreds of dead fish. Since the beginning of this crisis, members of IDSM and at least 21 other organisations, including WWF-Brazil, have been racing against time to mitigate the impacts of the environmental and health emergency that hit Lake Tefé, in Middle Solimões River, inner state of Amazonas.
 

Heat and fire

With warmer air and drier forests, fires spread and worsen the problem even further. Fire releases large quantities of aerosols into the atmosphere, particles that, under normal circumstances, are emitted by the forest itself, favouring the formation of rain, as it is around them that water condenses to form clouds. With the fire, huge amounts of aerosols are emitted into the atmosphere, but as there is little water vapour in the atmosphere, cloud formation is suppressed and ends up only occurring at high altitudes.

“Due to the altitude, these rains are freezing and sporadic, insufficient to recharge the rivers. But they often form storms with strong winds, which can knock down trees. In this drought, we have even seen hail here in Manaus, even with extremely high temperatures in the city”, says Schöngart.

The researcher says that, at the moment, the heat is much more intense than normal in Manaus and that, a few days ago, a fire in a forest fragment in the vicinity of his residence made the local scene hellish. “I still have in my mind the images of the region completely flooded just two years ago and now we see everything dry and in flames. There is no doubt that the situation is serious in the Amazon with these extremes. In the last 15 years, we have had the four biggest floods and the two biggest droughts in history in the Central Amazon region,” he says.
 

Big trees

This process will have a dramatic impact on Amazonian trees. “Large trees take around two years to die, because they have reserves and their roots are deep and can access underground water. That's why we don't see many of them dying immediately. But, with the lowering of the water table, after two years, the stress is so great that the tree cannot bear it”, explains the researcher.

The taller a tree is, the more difficult it is to withstand extreme drought. “And it is precisely these large trees that are responsible for the stability of the forest. When they die, the vegetation on the edges of the deforested area is altered. There is a greater incidence of lateral light, an invasion of grasses begins, which proliferate and become fuel for fires. This process leads to more trees dying and there is a progressive effect, like a domino, leading to the total degradation of the forest", explains Ben Hur.

At this moment, while the drought is still severe, the fires are advancing across the southern Amazon. “There are vast areas where land grabbers produce arson and, in these climate conditions, the flames spread very easily - and then the catastrophe is complete”, states Beatriz.

This combination of factors leads to forest degradation in increasingly larger areas of the Southern Amazon. The data collected by both scientists indicates that several areas are already showing signs of collapse - and are a clear example of the known degradation process that could spread across the Amazon.

"The situation in several of the regions where we work is dramatic, with forests degrading rapidly, streams drying up and small rivers becoming intermittent. This is all on the southern edge of the Amazon, from where the problem progresses rapidly towards the centre of the biome", says Ben Hur. According to him, in these degraded areas, tree mortality is high and the number of species is reduced. This has an impact on the entire food chain, reducing the area's biodiversity across the board.
 

Structural degradation

The process is modifying the structure of the forest itself - which jeopardises all its ecological services, including the formation of "flying rivers", which ensures rainfall in the rest of the continent. "What we find in these degraded areas are Amazonian pioneer species that begin to take over the environment. The structure of the forest begins to change and, instead of the highly diverse primary forest, what we find is a completely degraded secondary forest," he said.

A study carried out by the couple and published in 2014 shows that transitional forests - typical of the south of the Amazon - are hyperdynamic, that is, they have high species mortality, but they also have a great capacity to establish themselves with the "recruitment" of new individuals. "The problem is that this dynamic has reversed and the 'recruits' are unable to return. As a result, mortality begins to predominate. We have observed this process, which is evidence of a tipping point", says Beatriz.

With this ongoing process, the forest becomes more vulnerable and researchers have observed, for instance, that fire now affects areas that previously did not burn. "We also noticed that large trees are often dying due to breakage. Apparently this happens because the intensity of the winds has become greater", says the researcher.

In these conditions of degradation, the forest's resilience to fire is much lower, according to Ben Hur. "Normally, when the forest loses biomass, it naturally recovers later and the balance of the entire biome is maintained. But the greater the number of trees lost, the greater the loss of shade. This intensifies the effects of drought and further reduces the level of rainfall, which tends to worsen the entire situation. It's a domino effect that can reach unimaginable levels."
 

What WWF-Brazil is doing

WWF-Brazil has been working in partnership with the Mamirauá Sustainable Development Institute, which is leading the rescue of river dolphins in the Tefé region, inner state of Amazonas, providing fuel, Personal Protective Equipment (PPE), veterinary supplies and logistical support to the displacement of volunteers.

We are also in contact with local partners and mobilised to support them in facing the humanitarian crisis caused by the drought in the Amazon region, as the consequences are especially dramatic for the most vulnerable populations, such as indigenous people, quilombolas, extractivists and riverside communities. At this moment, our main area of activity is supplying food to communities impacted by shortages.