The impending loss of the Amazon rainforest due to deforestation has concerned scientists, activists, and citizens all over the globe. Natural habitats sustaining the region’s incomparable biodiversity and important carbon stores are at stake, with far-reaching implications for the global climate.

Previous studies warned that the Amazon was moving towards a tipping point, beyond which the forest would lose the ability to sustain itself and thus turn into a savannah. But new research suggests that this might not be the case.

Scientists from the Max Planck Institute for Meteorology (MPI-M) have revealed that the Amazon region sustains precipitation even if it were completely deforested. The work is published in the journal Geophysical Research Letters.

Tipping point argument was based on simplified models

The reason for scientists to fear a tipping point was the importance of the vegetation for making rain. Plants transport water from the soils via their leaves to the atmosphere, thereby creating moisture that sustains precipitation in the Amazon region. The combined capacity of soils and plants to deliver moisture to the atmosphere is known among experts as evapotranspiration.

The conceptual argument that deforestation leads to a reduction in evapotranspiration and thus in precipitation was supported by numerous modeling studies.

However, they all had important limitations: the studies were either conducted with global climate models that used a simplified representation of convection, the main atmospheric process that transforms moisture into rain in the Amazon, or they were based on regional models that do not allow for the large-scale atmospheric circulation to adapt to deforestation.

Now, for the first time, MPI-M scientists Arim Yoon and Cathy Hohenegger used the global storm-resolving ICON model to overcome both of these limitations. They ran a global simulation for the atmosphere with a horizontal resolution of five kilometers and over a time period of three years. Instead of using simplified rules of thumb, convection was explicitly resolved in the model.

Wind carries moisture into the region

The results show that precipitation in the Amazon is not as dependent on evapotranspiration as previously thought. Rather, the loss of evapotranspiration due to deforestation is compensated by changes in the large-scale circulation.

“The wind at about three kilometers altitude carries enough moisture from the ocean into the region to make up for the decline in evapotranspiration,” says Yoon. According to the computations, mean annual precipitation in the Amazon does not change significantly even after complete deforestation. This is in contrast with previous findings.

“Precipitation over land seems more tightly coupled to the large-scale circulation than to evapotranspiration in our global storm-resolving simulation if compared to state-of-the-art climate models currently used in the IPCC assessment reports. This fact is exciting as it asks for the revisitation of some of the things we thought we knew about precipitation over land and its sensitivity,” says Hohenegger.

However, while the total amount of rainfall in the Amazon during one year isn’t projected to change, the distribution of rainfall throughout the year is. “Just using one indicator to assess the future of the Amazon rainforest isn’t enough,” Yoon says. “The details of the rainfall patterns can make a big difference.”

As a next step, the researchers want to use the same simulation to investigate if extreme rainfall and extreme drought are becoming more frequent or more intense.

So, the study is good news, but not an all-clear: even though deforestation doesn’t significantly reduce mean annual precipitation, it still changes the regional and the global climate and has adverse impacts on the ecosystem, and the people that depend on it.