New research suggests that tropical forests across South America, Africa, and Southeast Asia are experiencing a steady rise in drought stress, raising concerns that some regions may be approaching a critical ecological threshold beyond which forest systems could weaken significantly or shift to alternative ecosystems.
The study, published in geophysical Research Letters analyzed nearly four decades of satellite observations and climate records from 1982 to 2019. Researchers found a clear upward trend in vegetation drought stress, driven not only by reduced rainfall in some regions but also by rising temperatures that increase evaporation and atmospheric drying.
Rising drought pressure across the tropics
Tropical forests are highly sensitive to changes in water availability. Under drought conditions, trees close small pores in their leaves to conserve water, a process that reduces photosynthesis and limits carbon dioxide absorption. When droughts become frequent or prolonged, this stress can slow forest growth, increase tree mortality, and reduce the ecosystem’s ability to store carbon.
The study shows that drought affected vegetation has expanded across much of the humid tropics, with the strongest increases observed in African tropical forests, though similar patterns are also emerging in parts of the Amazon and Southeast Asia.
Tropical forests play a central role in regulating Earth’s climate by absorbing large amounts of carbon dioxide through photosynthesis. However, this carbon sink depends on forests remaining healthy and resilient. Increasing drought frequency reduces this capacity, potentially weakening one of the planet’s most important natural climate buffers.
Researchers also highlight that forests contribute to regional rainfall through moisture recycling. As vegetation stress increases, this feedback loop may weaken, potentially reinforcing dry conditions in already vulnerable regions.
Scientists warn that continued warming and drying could push some forest systems toward “tipping points,” where gradual stress leads to rapid and potentially irreversible ecosystem change. In extreme scenarios, parts of tropical forests particularly in the Amazon could transition toward more open, savanna like landscapes.
While the study does not conclude that such a shift is imminent, it emphasizes that increasing drought frequency may indicate that some ecosystems are approaching their tolerance limits.
Model limitations and uncertainty
The research also finds that many current climate models do not fully capture the complexity of vegetation atmosphere interactions in tropical regions. This creates uncertainty in predicting how forests will respond to future warming, with some areas potentially more resilient and others more vulnerable than models suggest.
Despite these concerns, scientists stress that widespread tropical forest collapse is not inevitable. The future trajectory depends strongly on global greenhouse gas emissions, deforestation rates, and forest protection efforts. Intact, undisturbed forests are generally more resilient to drought than fragmented or degraded landscapes.
The findings add to growing evidence that climate change is altering not just extreme events but the long-term stability of Earth’s major ecosystems, with tropical forests now showing signs of increasing stress under a warming and drying climate.