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If the Amazon rainforest were completely cleared, extreme precipitation, heat stress, and high wind speeds would occur more frequently. This is the result of a recent study based on simulations using a kilometer-scale climate model.
From a bird's eye view, the Amazon rainforest appears as a lush green mosaic of tree tops stretching as far as the eye can see. It is home to countless animal and plant species, many of which are endemic, and the forest plays an important role in the global climate as a carbon sink. However, deforestation threatens to destroy this unique ecosystem and its important functions. One-fifth of the area has already been cleared, and there is no end in sight to this intensive use. This has serious consequences for biodiversity and the global and regional climate. Taking advantage of a unique global km-scale climate simulation, a recent study by the Max Planck Institute for Meteorology (MPI-M), the University of Hamburg, and the Institute of Science and Technology Austria, shows that extreme precipitation, heat stress, and wind speed increase significantly in a scenario of complete deforestation, making forest recovery very difficult.
The study was led by Arim Yoon and Cathy Hohenegger (both MPI-M) and builds on an earlier study by the two researchers. Using a global km-scale model, they had shown that the mean annual precipitation in the Amazon region would not change even after complete deforestation. Based on the same simulations, the new study shows that the situation looks different for extreme events. To resolve the short-term and small-scale nature of these events, the model’s fine grid-spacing of five kilometers and detailed physical representation of the processes leading to the formation of rain were essential.
More downpours, heat, and stronger winds
The analysis showed that in a scenario where the rainforest is completely cleared, the distribution of hourly precipitation becomes more extreme: Heavy rainfall of more than 50 mm per hour increases by 54 percent, and hours with no rain by as much as 173 percent. In addition, compared to an intact forest, the temperature rises by almost four degrees Celsius. Temperature fluctuations are stronger, and extreme wind speeds more frequent.
“Tropical plants are actually adapted to relatively steady environmental conditions,” says lead author Arim Yoon. “When extreme events increase, it can make it very difficult for the forest to recover.” In addition, people living in the region are severely impacted, as the authors demonstrate using various heat stress indicators. The only heat stress indicator which is not increasing is the wet bulb temperature, which also takes into account changes in humidity, as in that case the increase in temperature is compensated by the drier conditions following deforestation.
The analysis also shows why extremes are increasing. After deforestation, the plant-mediated transport of moisture from the land into the atmosphere, called evapotranspiration, decreases. As a result, it is generally drier, there is less convection, and periods without rain are more frequent. However, stronger updrafts due to large-scale convergence lead to more intense precipitation. The increase in temperature is due to lower evapotranspiration and a corresponding increase in sensible heat. And the stronger wind speeds are caused by both the lack of trees to “slow down” the air and by downdrafts from the more intense thunderstorm cells.
Long-term or large-scale averages do not provide any information about extremes. According to the researchers, it is therefore important to consider various indicators on short time scales when assessing the changes and to use tools that can represent those fast and small-scale fluctuations. Even though the current findings are based on a hypothetical scenario, they still provide a clear warning about the consequences of ongoing deforestation in the Amazon region.
Dr. Arim Yoon, Max Planck Institute for Meteorology: arim.yoon@mpimet.mpg.de
Dr. Cathy Hohenegger, Max Planck Institute for Meteorology: cathy.hohenegger@mpimet.mpg.de
Yoon, A., Hohenegger, C., Bao, J., and Brunner, L. (2026): Extreme events in the Amazon after deforestation, Earth Syst. Dynam., 17, 167–179, https://doi.org/10.5194/esd-17-167-2026.
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