Vast areas of the Amazon rainforest are cleared for cattle ranching Michael Dantas/AFP via Getty Images
The alarming rate of deforestation is significantly diminishing rainfall patterns across the Amazon, indicating that this vital rainforest could hit a catastrophic tipping point sooner than previously anticipated.
Research from 1980 to 2019 indicates that rainfall in the southern Amazon basin has diminished by 8 to 11 percent, based on satellite data and rain gauge readings. During this same time frame, tree cover in the region has shrunk by 16 percent, primarily due to deforestation linked to beef cattle ranching.
Contrastingly, deforestation has been less pronounced in the northern Amazon Basin, where precipitation has only shown minor increases that lack statistical significance.
Recent research highlights that deforestation contributes to arid conditions within a 300-kilometer radius. This new analysis reveals that this effect spans over a basin wider than 3,000 kilometers, suggesting that deforestation harms not just forests, but also the productivity of adjacent ranches and soybean farms, according to Dominique Spracklen from the University of Leeds.
“Some in agribusiness may perceive sections of the forest as underutilized land. Yet, these forests play a crucial role in maintaining regional rainfall, which in turn benefits our agricultural practices,” Spracklen explains.
Global warming is exacerbating the drying of the Amazon, culminating in extreme droughts and unprecedented wildfires in 2024. However, atmospheric studies led by Spracklen and colleagues indicate that deforestation is responsible for 52 to 75 percent of the decline in rainfall.
Moisture from the Atlantic Ocean is transported by prevailing winds into the Amazon, where it precipitates as rain. Plants contribute to this cycle as evaporation and transpiration return about three-quarters of that water to the atmosphere. Further downwind, it falls again as rain through multiple cycles, creating “flying rivers” that distribute moisture across the rainforest.
When forested areas are destroyed, over half of the rainwater is redirected to rivers and subsequently returns to the ocean, depleting the moisture available for the flying rivers and leading to reduced rainfall. Additionally, this diminishes atmospheric instability necessary for storm cloud formation, Spracklen and his team discovered.
As fewer trees slow down the wind, it tends to pick up speed, removing more moisture from the area.
Unlike previous research, this study employs a combination of data and modeling to effectively illustrate how deforestation impacts rainfall patterns, asserts Yadvinder Malhi from Oxford University.
“The atmosphere becomes smoother and, in a sense, slipperier. There’s reduced friction with the ground, enabling moisture to travel further out of forested regions,” Malhi notes, emphasizing the significance of secondary atmospheric processes often overlooked in prior studies.
Scientists voice concerns that the cumulative impact of heightened temperatures, drought, and deforestation could push the Amazon rainforest to a tipping point where it transitions into a savannah ecosystem, although the timeline for this transition remains uncertain. Spracklen and his colleagues found that climate models may underestimate the influence of deforestation on rainfall by as much as 50 percent, implying that the rainforest could face significant threats earlier than anticipated.
According to a 2022 study, there is a 37% probability that certain regions of the Amazon could vanish by 2100 if global temperatures, currently at 1.4°C, rise to 1.5°C. However, this does not necessarily imply that rainforests will convert into savannahs; it may lead to the emergence of fewer species and scrub forests capable of storing less carbon.
“The Amazon’s sensitivity is greater than we previously imagined, which is troubling,” he states. “We may be closer to the deforestation threshold than we realize, although there remains significant uncertainty surrounding this issue.”
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Source: www.newscientist.com
