A warning: human activity causing the Amazon’s waters to dry up

Studies conducted by WWF-Brazil in partnership with Imazon and NASA reveal that the conversion of native vegetation and indiscriminate construction of infrastructure are affecting the water resources of the planet’s largest tropical forest

By WWF-Brazil

Using information from NASA

Photo: Márcio Nagano

When thinking about the Amazon, the first thing that usually comes to mind is the conversion of the native forest, or perhaps more recently the fires that destroyed over 16,000 km2 of forest, representing a 26% increase compared with the same period in 2018 (more information in the box to the side). But there is another more silent threat to the planet’s largest tropical forest: water loss.

A new type of study performed by WWF-Brazil and the Amazon Institute of People and the Environment (Imazon), which was recently published in the scientific journal Water (MDPI), reveals some extremely worrying data: on average, 350 km2 of aquatic environments have been lost per year since the 1980s – including wetlands, mangroves and lakes.

“This loss means that every year there is less water than expected in the Amazon. Small rivers and lakes are reducing in area and volume, and wetlands are starting to disappear,” claims Bernardo Caldas, a conservation analyst for WWF-Brazil. “This has serious consequences for both the environment and for people, as reduced wetlands mean lower fish populations, fishing stocks and protein for consumption by the local population.”

The study conducted by WWF-Brazil and Imazon demonstrates that this reduction in wetlands is caused by alterations to rainfall patterns, as well as the conversion of native vegetation, land use and indiscriminate implementation of infrastructure projects, such as hydroelectric dams. Large infrastructure projects affect the natural dynamics of the ecosystem and cause alterations to water courses and water flow, which go on to have an effect on the entire system.

The area identified as containing multiple human interventions also happens to coincide with the “deforestation arc” located in the southern Amazon.

“We need a strategic environmental plan that takes into consideration the impact of both large infrastructure projects and the combination of thousands of small projects that can affect the water basin. These can include projects focused on water supplies for local populations, animal rearing, agricultural activities, community food security and tourism, as well as the need for ecosystems to have enough space and time to ensure their own self-maintenance,” concludes Caldas.

Researcher for Imazon, Carlos Souza Jr., says that the NASA study reinforces the hypothesis that the climate is also contributing to this process. “The hypothesis in our study is that there are two vectors contributing to the loss of groundwater in the Amazon: land use and climate change. We identified alterations to land use, with the conversion of native vegetation causing a rupture in the drainage network and impacting small rivers and lakes,” stated Souza.

Next steps

Imazon intends to continue its investigation into the effects of water loss on the Amazon. “Our next investigation will analyse how this reduction of water will affect traditional and indigenous populations, food and energy production and biodiversity. Lower water levels could represent one of the first obvious signs of a tipping point in the Amazon. We need to understand how the combined effect of the climate and land use can accelerate this process and affect other ecosystems. We are at a crucial moment in which science needs to be understood by society and seriously considered in public policies directed at the region,” says Souza Jr.

NASA research

A NASA study published at the end of October corroborates the data obtained by WWF-Brazil and Imazon. The paper demonstrates that the atmosphere over the Amazon rainforest has been drying up over the last 20 years, increasing the demand for water and leaving ecosystems vulnerable to fire and drought. It also shows that this increase in dryness is mainly the result of human activity. “The change in atmospheric dryness is way beyond what we would expect as a result of natural variations in the climate,” says Armineh Barkhordarian from NASA’s Jet Propulsion Laboratory, the main author of the study.

“It is a matter of supply and demand. Increased temperatures and drier air above the forest lead to trees needing more moisture from the soil as part of the transpiration process. But the soil doesn’t contain this extra water for the trees,” explains Sassan Saatchi, co-author of the study. “Demand is increasing, supply is decreasing, and if this continues the forest may no longer be able to sustain itself.”

Why losses in groundwater and atmospheric moisture are worrying

Trees and plants take in moisture from the soil and transpire water vapour into the atmosphere through the pores in their leaves. This cools down the air and eventually rises to form clouds and rain. Tropical forests can generate up to 80% of their own rain, especially during the dry season.

The loss of water in the Amazon impacts both the local ecosystem and Brazil as a whole through reductions in aquatic ecosystems and their populations, as well as other countries such as Bolivia, Paraguay, Argentina and Uruguay, which receive water vapour from the biome carried on air masses. A reduction in groundwater causes the moisture content of the atmosphere to decrease, subsequently leading to less rainfall.

Two studies

The study by WWF-Brazil and Imazon used Landsat satellite images collected over 33 years (1985 to 2017), new data-processing computer cloud technology and a dedicated analysis involving Imazon’s partners. The NASA study, “A Recent Systematic Increase in Vapour Pressure Deficit over Tropical South America”, was published in October in Scientific Reports. The scientific team used data from NASA’s Atmosfer Infrared Sounder (AIRS) instrument on board the Terra satellite.