Many scientists believe the Amazon, encompassing the world's largest tropical rainforest, could soon reach a
where it starts to dry up and can no longer sustain rainforest. Some even predict that rainforest will ultimately be transformed into savanna-like ecosystems. However, until now, inception of such an irreversible transition has not been supported by observations.
A new study, published in Environmental Research Letters
, showed how deforestation is triggering an irreversible transition in Amazon hydrological system, recognized as a key process that can prompt a tipping point to a treeless Amazon. This study was led by scientists from the Institute of Atmospheric Physics at the Chinese Academy of Sciences.
According to this study, deforestation causes substantial reduction in evapotranspiration, leading to drier lower atmosphere up to the middle troposphere, although moisture supplies from tropical Atlantic have been enhanced due to the warming ocean surface.
"Over the past 20 years, desiccation—the removal of moisture— in the lower troposphere has been persistent during the dry season and emerging in the wet season." said Dr. XU Xiyan, the first author of this study. "This occurs because deforestation induces warming-enhanced buoyant updrafts, elevates hot and dry air and thereby reduces downward mixing of water supplies from the tropical Atlantic." They find the atmospheric drying is particularly severe in the southeastern Amazon where deforestation is extensive.
"The severe atmospheric desiccation cannot be compensated by enhanced water supplies from the Atlantic Ocean, demonstrating an emerging transition in Amazon hydrological cycle." said Dr. JIA Gensuo, the corresponding author of the study, further explained.
That being said, scientists also have some encouraging findings. According to the study, the drying over the north part of Amazon rainforest has just occurred, suggesting a window of opportunity for preventing ecosystem collapse with forest conservation. "Large scale forest conservation and ecological restoration are still promising and offer the opportunities for reversing the drying trend and preventing ecosystem collapse", said Dr. JIA.
Forest conservation and restoration have been practiced at large scale in Brazil and other Amazonian countries in past decades, which is considered to positively mitigate climate change and maintain hydrological and ecosystem services.
This study was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences, and U.S. Department of Energy, Office of Science, Biological and Environmental Research, Regional and Global Climate Modeling program through the RUBISCO Scientific Focus Area.
Reference: Xu, X., X. Zhang, W.J. Riley, Y. Xue, C.A. Nobre, T.E. Lovejoy, G. Jia*, 2022: Deforestation triggering irreversible transition in Amazon hydrological cycle. Environmental Research Letters, 17, 034037. https://doi.org/10.1088/1748-9326/ac4c1d
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