Evapotranspiration
The Amazon rainforest—rich in biomass and biological productivity—has an enormous evapotranspirative capacity. A substantial portion of the rainfall in the basin is generated internally through this process. This is particularly true for the southern Amazon, where seasonal rains are more limited and evapotranspiration plays a crucial role in maintaining the ecosystem’s wet conditions.
Deforestation reduces vegetation, which reduces evapotranspiration, which in turn lowers regional humidity and decreases precipitation. This can initiate a feedback loop: less rain leads to more forest dieback, which further reduces evapotranspiration. As a result, rainforest can shift into seasonal tropical forest or even savanna.
According to Kimbrough (2022), the loss of 25% of the Amazon’s original forest cover could push the region past a tipping point, triggering the conversion of an additional 31% into savanna. This shift would be most dramatic in the southern and eastern Amazon, where seasonal dryness is already increasing.
As Watts (2024) reports, crossing this threshold could place 50% of the Amazon rainforest under stress, and likely result in an additional 19% transitioning to seasonal tropical forest. In other words, only 25–30% of the Amazon may retain its original, humid rainforest character if this tipping point is crossed.
The consequences go beyond forest structure. Reduced evapotranspiration can also lower river water levels, affecting navigation, fisheries, and hydropower.
Evapotranspiration is both a casualty of deforestation and a critical climate mechanism—when it's disrupted, the entire rainforest system is at risk. We haven’t crossed the tipping point yet—but the data suggests we're moving dangerously close.
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