Study Reveals Drought in Amazon Rivers Impacts Both Local Communities and National Territory
The Amazon rivers are of great importance in Brazil, whether for supplying cities, agricultural and livestock development, or the way of life of riverside populations. Thus, droughts in its watercourses , such as the one that occurred last year, on the Negro River, one of the largest tributaries of the Amazon River — being one of the most intense droughts ever recorded, with the river reaching 12.70 meters, its worst mark in 121 years since hydrological measurements were installed — are extremely harmful.
According to Cleide Rodrigues, professor at the Faculty of Philosophy, Letters and Human Sciences (FFLCH) at the University of São Paulo, rivers can be classified as ephemeral (occurring only during rainy events), intermittent (occurring seasonally) or perennial (occurring year round), depending on geographic location, hierarchical order of rivers and river basins, as well as structural and geomorphological factors. “Amazonian rivers are, for the most part, classified as the latter type, due to the location of their basins predominantly in a humid tropical climate,” she states.
“Common sense mistakenly interprets this condition of remarkable perpetuity and high magnitudes of Amazon river flows as being the mark of regular regimes and high predictability. However, in recent decades, there has been an accumulation of primary climatological and fluviometric data associated with satellite information sufficient to recognize the great spatial variability of annual regimes between the different basins that make up the Amazon rivers, as well as the large annual amplitude of river flows, whether basins on the left or right bank”, explains the teacher.
Reason for droughts
Cleide also states that the Negro River basin, being part of the left bank of the Amazon basin, is located in an area with less anthropogenic impact, compared to the rest of the Amazon. “It is also characterized by this condition of an annual river regime with marked seasonality, as well as a high magnitude of elevation variation. These variations, throughout the hydrological year, are expected and are very characteristic, being strongly associated with the daily life of riverside populations and forming part of the knowledge of traditional people. However, what some scholars have observed is an increase in the frequency of extreme drought and flood events in the last two decades, even though we have time series of approximately 100 years or less”, he adds.
The geographer also explains that in Amazonian rivers, such as the Negro River, there are well-established correlations between extreme hydrological processes and global atmospheric systems — such as La Niña and El Niño — with regard to their performance and their effects on seasonal movements of water. Intertropical Convergence Zone (ITCZ). In this sense, Wagner Costa Ribeiro, professor at FFLCH and researcher at the Institute of Advanced Studies (IEA), also at USP, comments that there are multiple causes that lead to this drought in the Amazon and that, according to some studies, it should occur every 350 years.
“Some studies associate it with the El Niño phenomenon, which is the warming of the waters of the Pacific, other studies will say that what happened, in fact, was a warming of the waters of the Atlantic, and that this would generate this climate anomaly. Then we have deforestation, which is accelerated and also contributes a lot to the increase in local temperatures, and this sum of factors causes us to have a reduction in rainfall”, he adds. According to the professor, the removal of vegetation cover along bodies of water prevents several benefits that trees bring — producing shading, protecting river banks and carrying out evapotranspiration — and adds to global warming — which changes atmospheric dynamics, the distribution and intensity of rainfall — as possible causes of the increased frequency of these droughts.
Nathália Nascimento, researcher and postdoctoral fellow at IEA-USP, states that there is already scientific evidence that proves the anthropogenic origin of the most recent droughts in the Amazon, influenced by changes in the climate — especially the increase in temperature and decrease in rainfall in the region. “For example, throughout the 20th century we had eight droughts, and from 2000 to 2023 we have already had five droughts, with the one in 2023 being the most intense. So, today, we already know that, in addition to these droughts being influenced by changes in the climate, the tendency is for them to increase, both in frequency and intensity of impact”, she comments.
Impacts on the population
The researcher explains that, firstly, it is important to understand that traditional populations and extractive communities in the Amazon have a very particular relationship of coexistence with nature. “So, the communities that live along the Amazon rivers, for example, have the river not only as their source of water, but also as their source of food, their transport route, their leisure space. It is the movement of this river, high and low, that determines when to plant and when to harvest”, she informs.
“When you have a drought event as extreme as the one we have observed since last year, this population, which directly depends on this water resource for the most varied purposes, ends up in a situation of water insecurity, food insecurity, inability to transportation to other regions, communities or closer cities”, he adds. Nathália states that this also affects the ability to reproduce this population’s way of life, as the agricultural and fishing routine is compromised after the loss of resources and spaces in which these activities can be developed and taught to other generations.
The post-doctoral student explains that, despite the forecast increase in the frequency of these droughts and the intensification of their impact on the riverside population, mass migrations are difficult to occur due to the strong relationship between these people and rivers, with a symbolic and even sacred value. with the territory in which they live. “So, the migration of this population in the Amazon to other regions or cities is very complex. I am not aware that any migration of the type caused by drought has started, but this is not impossible to happen in the future”, she adds.
Regarding the regional and national impacts, Ribeiro states: “When there is greater intensity of evapotranspiration from the forest, part of this water is lost, and then that natural flow that we know, called flying rivers, stops occurring with the known intensity. Much of this humidity comes from evapotranspiration associated with the rains of the Amazon, forming a very rich, very large volume of water, which meets the Andes Mountains and heads to the left, bringing this humidity to the South and Southeast of the country. ”. In this way, he says that water evaporation reduces agricultural production capacity, characterizing an agricultural drought, which affects not only on a local scale, but also the South and Southeast.
Impacts on fauna and flora
Agustín Camacho, researcher at USP’s Biosciences Institute (IB), explains that the Amazon basin is naturally subject to strong fluctuations in water levels. “Periods of drought are followed by periods of heavy rain, and this is what causes such fluctuations. Today, climate change and deforestation appear to be increasing these swings,” he reports.
“The Amazon rainforest has many organisms, and each of them has specific tolerances that determine the conditions in which these organisms can survive. When drought arrives, it imposes two types of stress on organisms: on the one hand, it obviously reduces the availability of water, but, on the other, temperatures also become more extreme, which means that organisms must face both challenges. at the same time,” he says.
In this way, Camacho explains that he carried out research to understand how the tolerance of some animals to high temperatures varies with the lack of water. “The results of the studies showed that dehydration caused by drought makes these animals less tolerant and much more vulnerable to increases in temperature. To give you an idea, when considering the combined effect of dehydration and high temperatures on Amazon lizards, the number of populations expected to be vulnerable to climate warming has tripled throughout the Amazon,” he reports.
Future
Ribeiro says that the reduction in deforestation in Brazil last year is insufficient, despite being a good way to avoid the increase in extreme weather phenomena. “We also need to combat climate change to prevent this other, more macro factor, from bringing disastrous effects to the Amazon. It is a very large group of actors who must, as soon as possible, propose an emissions reduction agenda”, he concludes.
Nathália states that the future prospects are not good, if there is no urgent change in attitude, and comments that a future with increasingly frequent and intense droughts would bring about a chaotic scenario, in which the forest itself would lose its ability to grow and of survival, resulting in impacts on water resources and in climatic situations unfavorable to human survival. “We need to act responsibly in protecting forests, in restoring areas that have been and are being deforested”, she concludes.