Amazonia: deforestation reduces rainfall

A recent publication by CNR's Institute of Atmospheric Sciences and Climate in Global Change Biology reveals that the impact of deforestation on rainfall in the Amazon region is greater than expected and could lead to an annual reduction of 55-70%. The work was conducted in collaboration with the University of Utrecht (Netherlands).

© Ivars Utināns on Unsplash

The Amazon rainforest generates some of the rain that falls in its own area, as it takes water from the soil and transpires it into the surrounding air, thus sustaining itself. A study by the Institute of Atmospheric Sciences and Climate of the National Research Council of Turin (CNR-Isac), published in Global Change Biology, reveals that the forest’s contribution is greater than previously thought. “Small changes in air humidity, due to the presence or absence of trees, can lead to large changes in observed rainfall,” says Mara Baudena, a researcher at CNR-Isac and first author of the research. “These amplifications had not been considered so far. In this study, we analysed precipitation and humidity data for more than ten years at hourly scales over a large part of the Amazon rainforest and neighbouring areas, in combination with data and models developed in previous work by Utrecht University in the Netherlands, which calculate how moisture is transpired by plants and transported by winds throughout the Amazon.”

The new estimates have important implications. “In the most extreme case, if the entire forest were to be cleared, our estimates suggest that annual precipitation in the area would fall by 55-70%,” continues the CNR-Isac researcher. “However, the data must be treated with caution: these new estimates are an important step forward in our level of knowledge, but they are not without uncertainties and approximations. We will need to continue research using different methods to confirm them,” adds Arie Staal, from Utrecht University. However, the authors are confident that the result obtained is qualitatively significant. “Even relative deforestation could have more dramatic effects than expected on rainfall, forest and neighbouring areas, home to crops and livestock that are often the source of deforestation itself,” Baudena concludes. “On the other hand, reforestation of already deforested areas could lead to important effects on the restoration of the water cycle and rainfall.

© CNR – The effects of deforestation and reforestation on rainfall in the Amazon. Small changes in air humidity, due to the presence or absence of trees (on the horizontal axis in the graph), can lead to large changes in observed rainfall (vertical axis).

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