Evapotranspiration
The Amazon rainforest helps sustain the rainfall it depends on through evapotranspiration. This process combines evaporation from soil, water, and wet vegetation with transpiration—the release of water vapor from plants through their leaves. Trees absorb water through their roots and return much of it to the atmosphere, where it can contribute to cloud formation and further rainfall.
Moisture arriving from the Atlantic Ocean supplies the basin with water, but the forest repeatedly recycles part of that water as air moves inland. This recycling helps maintain humid conditions and supports forests farther downwind. It is especially important in regions where a pronounced dry season already places trees under water stress.
Deforestation disrupts this cycle. Replacing rainforest with pasture or cropland generally reduces evapotranspiration, particularly during the dry season. Less moisture returns to the atmosphere, potentially reducing rainfall and making the remaining forest more vulnerable to drought and fire. As additional trees die, moisture recycling weakens further.
This feedback is central to concerns about an Amazon tipping point. If drying and forest loss reinforce one another strongly enough, some areas could undergo a persistent shift toward more open, degraded vegetation or savanna-like conditions. The damage could therefore extend beyond the land directly cleared.
The threshold is uncertain, however. The Amazon is a vast and varied region, and its forests do not all respond in the same way. The location of deforestation, rising temperatures, drought, and repeated fires all influence whether forests can recover. A single percentage of forest loss cannot fully describe these interacting pressures.
Research reported by Watts (2024) estimated that 10–47% of Amazonian forests could face interacting disturbances by 2050, potentially triggering major ecosystem transitions. This describes exposure to risk, rather than a prediction that the entire affected area will become savanna. Watts, 2024
Changes in moisture recycling can also affect rivers and the people who depend on them. The relationship is complex: reduced evapotranspiration can initially leave more water available for runoff, while a sufficiently large decline in rainfall can reduce river flows. Changes in water availability can consequently affect navigation, fisheries, agriculture, and hydropower. Makarieva and colleagues, 2022
Evapotranspiration connects the Amazon’s vegetation to its climate. Protecting the forest helps preserve the moisture recycling that supports both remaining trees and ecosystems downwind. Although the timing and extent of possible transitions remain uncertain, limiting deforestation, preventing repeated fires, and reducing global warming can help keep those pressures from reinforcing one another.
References:
Kimbrough, Liz. (September 20, 2022) How close is the Amazon tipping point? Forest loss in the east changes the equation Mongabay
Watts, Jonathan. (February 14, 2024) Amazon rainforest could reach ‘tipping point’ by 2050, scientists warn The Guardian