Deforestation in the Amazon raises the surface temperature by 3 °C during the dry season

(Press-News.org) Deforestation in the Amazon is causing significant regional changes in climate compared to areas with forest cover above 80%. The loss of vegetation leads to an increase in surface temperature, a decrease in evapotranspiration, and a reduction in precipitation during the dry season and in the number of rainy days.

The results are part of a study based on satellite data published in late November in the journal Communications Earth & Environment.

The study points out that highly deforested regions (with forest cover below 60%) share climatic similarities with areas of transition between rainforest and savanna. This is because the observed impacts include an average surface temperature that is 3 °C higher during the dry season and evapotranspiration and rainfall that are 12% and 25% lower, respectively, compared to regions with high forest cover.

Additionally, there were an average of 11 fewer days of rainfall where forest cover was less than 60%. In other words, deforestation impacted both the amount and distribution of rainfall.

These drier and hotter climatic conditions may lead to greater forest degradation, increased tree mortality, and greater susceptibility to forest fires. This scenario threatens the survival of more sensitive species in the rainforest while favoring the dominance of other opportunistic native and exotic species, thereby compromising biodiversity.

The findings highlight the urgency of controlling deforestation and restoring degraded areas to preserve the Amazon’s climate resilience and the economic activities that depend on it, such as agriculture.

“The study shows that tropical forests have a huge impact on the climate, with consequences for various sectors of society, both for the well-being of populations and for economic activities. Therefore, the debate on the importance of forests must take a more comprehensive view, beyond the environmental issue. We need to work with a vision of national development, with coordinated and integrated action between different sectors of society,” argues Luiz Aragão a researcher from Brazil’s National Institute for Space Research (INPE).

One of the authors of the study, Aragão is a member of the coordination team for the FAPESP Research Program on Global Climate Change (RPGCC) and participated in panels at the 30th United Nations Climate Change Conference (COP30) in Belém to discuss issues related to greenhouse gas emissions and the impacts of global warming.

According to Marcus Silveira, the first author of the article and an INPE researcher, the study scientifically corroborates the importance of maintaining at least 80% forest cover on rural properties in the Amazon, as stipulated in the Brazilian Forest Code.

This legislation establishes rules for land use and environmental protection on private property in legal reserves, requiring that a portion of rural areas be maintained with native vegetation. In the nine states of the Legal Amazon – an area designated by the Brazilian government for socio-environmental development that encompasses the federal units where the biome is found – native vegetation coverage is required on 80% of properties in forested areas, 35% in the Cerrado (tropical savanna region), and 20% in open fields – the same percentages as the rest of the country.

“Deforested regions suffer from drier and hotter conditions, which also end up affecting agricultural production. The Food and Agriculture Organization of the United Nations [FAO] itself released a document at COP30 showing that forests are allies of agribusiness, not enemies. Through an extensive review of the scientific literature, it highlights the various climate benefits that forests promote, contributing to agricultural productivity and resilience. Our work is very much in line with that,” says Silveira, who, together with several Brazilian authors, collaborated on the report Climate and Ecosystem Service Benefits of Forests and Trees for Agriculture.

New uses

The Brazilian Amazon, which covers nearly half of the country, lost 13% of its native vegetation between 1985 and 2024. This equates to approximately 520,000 square kilometers (km²), which is larger than the territory of Spain (506,000 km²). This information comes from the publication Amazônia, Coleção 10 do MapBiomas, which is based on an analysis of satellite images.

During this period, pastureland increased from 123,000 km² to 561,000 km², and the area used for agriculture grew from 1,800 km² to 79,000 km². More recently, mining has gained importance, reaching 4,440 km² in 2024.

Despite the reduction in the rate of deforestation of the biome over the past three years, scientists emphasize the urgent need to halt the destruction of the forest. In 2024 alone, over 6,300 km² of native vegetation was removed in the Legal Amazon, according to the INPE’s Brazilian Amazon Forest Satellite Monitoring Program (PRODES).

“It’s essential that we chart paths to reduce deforestation, as discussed at COP30, but it’s also necessary to move forward with the process of replacing the use of fossil fuels to curb global warming, which is already a cause for concern,” Aragão told Agência FAPESP.

2024 was the hottest year on record and the first to exceed the 1.5 °C threshold of average temperature increase compared to pre-industrial levels. Additionally, the Global Carbon Budget report, released in November, states that carbon dioxide emissions from fossil fuels will increase by about 1.1% in 2025, resulting in a record 38.1 billion tons of CO₂ (GtCO₂).

“Our study indicates that if we manage to restore the forest structure, it’s also possible to bring back ecosystem services, such as temperature reduction, increased water cycling, and carbon stocks, thus ensuring greater water, food, and economic security for the country,” Aragão adds.

Step by step

For the study, which was part of Silveira’s doctoral thesis, the scientists divided the Amazon into a regular grid of samples measuring approximately 55 by 55 kilometers. The samples were grouped into levels of accumulated deforestation: remaining forest cover of up to 40%, 40 to 60%, and 60 to 80%. They also selected grids with high forest cover (above 80%) adjacent to deforested areas to serve as a reference for climatic conditions with little influence from deforestation.

The study employed other control methods to highlight the influence of native vegetation loss compared to other factors. For example, they compared climatic differences between neighboring reference regions. Eleven climatic variables were analyzed, including surface temperature, evapotranspiration, and annual and seasonal rainfall, as well as the number of rainy days.

Evapotranspiration is the flow of water vapor into the atmosphere from plant transpiration and the evaporation of water from soil and tree canopies. It is controlled by factors such as vegetation type and structure, temperature, solar radiation, and wind. Deforestation reduces evapotranspiration, contributing to increased temperatures and decreased atmospheric moisture recycling into rain.

The most extreme impacts were observed in regions with up to 40% remaining forest cover. For instance, the surface temperature in these regions was up to 4 °C higher than in the reference regions during the dry season. Similarly, evapotranspiration in the dry season was, on average, 45 millimeters lower than in neighboring reference regions.

This study was supported by FAPESP through scholarships for Silveira (22/11698-8 and 23/05733-8) and a grant for the Research Center for Greenhouse Gas Innovation (RCGI).

In September, the journal Nature Communications published another study led by scientists from the University of São Paulo (USP) that quantified the impact of vegetation loss and global climate change on the Amazon. The study showed that deforestation was responsible for 74.5% of the reduction in rainfall and 16.5% of the temperature increase in the biome during the dry months (read more at agencia.fapesp.br/55762).

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