Deforestation is closely related to reduced rainfall in the Amazon rainforest
Observations from 35 years of Amazon research show how global climate change and local deforestation affect the rainforest ecosystem
- New study quantifies climatic changes in the rainforest due to local deforestation and global climate change quantified separately
- Data show that deforestation is the main cause, accounting for 75 percent, of the decline in precipitation by 21-millimeter during the dry season since 1985.
- Global climate change is the main cause of the 2 Grad Celsius rise in temperature
The Amazon rainforest is the largest rainforest on Earth and plays a key role in the global climate system. In recent decades, however, major changes have been observed in the water, carbon, and energy cycles in the Amazon region, which influence precipitation levels, for example. However, previous studies have not yet been able in quantitatively differentiating the contributions of the two primary driving factors: rising global temperatures caused by greenhouse gas emissions and the increase in local deforestation.
Researchers from Brazil and the Max Planck Institute for Chemistry in Germany have successfully quantified the distinct impacts of local deforestation and global climate change on the Amazon region's climate.
Their findings, published in Nature Communications, reveal that local deforestation is the main reason why precipitation during dry seasons has decreased by almost eight percent, or 21 millimeters, since 1985. Luiz Machado, a climate researcher at the University of São Paulo, says: “Deforestation accounts for almost 75 percent of the decline in rainfall. Even small changes in rainfall during the dry season could therefore have a disproportionate impact on vegetation health.” In the dry season, only 26% of the average precipitation occurs, amounting to 281 millimeters, compared to 1097 millimeters during the rainy season.
According to the researchers, deforestation also accounts for about 16 percent of the 2°C temperature rise. However, a much larger share of about 84 percent of the temperature increase is attributable to global climate change. The study further indicates that the Amazon's climate does not respond linearly to deforestation, with the most severe climatic changes occurring early in the deforestation process, particularly when 10–40 percent of the forest is lost.
Amazon's climate resilience threatened by further deforestation
“It is important to stop further deforestation in order to preserve the climate resilience of the Amazon region,” adds Luiz Machado, who also works as visiting scientist at the Max Planck Institute for Chemistry in Mainz.
In their study, researchers analyzed data from 29 regions within the Brazilian Amazon, gathered over the past 35 years (1985 to 2020) using satellites and atmospheric measurements. By leveraging both long-term data and specialized statistical techniques (parameterization), they successfully distinguished the impacts of deforestation from those of global climate change.
The Brazilian-German team concluded that over 99 percent of the rise in greenhouse gases, such as methane and carbon dioxide, is due to global climate change. However, deforestation accounts for a small share of 0.3 percent of the increase in CO2.
Rainforest currently undergoing critical change
The study also examines the future climate of the Amazon region in 2035. Christopher Pöhlker from the Max Planck Institute for Chemistry states, “If deforestation continues at the current rate, our data indicate that we can expect a further temperature rise of about 0.6 °Celsius and a significant decrease in precipitation of about seven millimeters during the dry season compared to today. This will certainly put additional stress on the forest” Pöhlker and his colleagues observe that the Amazon is experiencing a critical transformation, which is likely to be accelerated by extreme events such as the extraordinary drought in 2023. However, the complex interactions between climate change and deforestation make it difficult to specify an exact level of deforestation that would lead to the collapse of the entire ecosystem of the Amazon rainforest.
Precipitation amount in millimeters
The amount of precipitation measured in millimeters is not affected by the size of the area, enabling direct comparisons across various locations and time periods. One millimeter of precipitation indicates an even layer of water 1 mm high covering each square meter of ground, equivalent to 1 liter per square meter.
Brazilian institutions involved
University of São Paulo, São Paulo, Brazil
MapBiomas, São Paulo, Brazil
Amazon Environmental Research Institute (IPAM), Brasília, Brazil