Deforestation in Brazil’s Legal Amazon drove roughly three-quarters of the region’s dry-season rainfall decline between 1985 and 2020, according to a peer-reviewed study that separated the effects of forest loss from those of global warming for the first time at this scale. The finding reframes the Amazon’s drying trend as a problem with a clear, local driver rather than a diffuse consequence of rising global temperatures. It also raises urgent questions about whether the remaining forest can sustain itself if clearing continues at recent rates.
How Researchers Isolated Deforestation’s Role
The study, published in Nature Communications, examined 29 areas of approximately 300 by 300 kilometers each across Brazil’s Legal Amazon. Using long-term atmospheric and land cover change data spanning 35 years, the team built a framework that could distinguish rainfall shifts caused by local deforestation from those linked to broader climate change driven by rising greenhouse gas concentrations.
That distinction matters because earlier research often treated the two forces as a single signal. By pulling them apart, the authors found that the total dry-season precipitation decline across their study areas averaged about 21 millimeters. Of that total, approximately 15.8 millimeters, or 74.5%, was attributable to forest clearing. Global climate change accounted for about 5.2 millimeters, a far smaller share.
The gap between those two numbers challenges a common assumption in policy discussions: that the Amazon’s drying is mainly a symptom of planetary warming that individual nations cannot control. Instead, the data suggest that decisions made within Brazil about land use have had a measurably larger effect on regional rainfall than the cumulative rise in global temperatures over the same period. For policymakers, that means curbing deforestation is not only about conserving biodiversity or reducing emissions; it is also a direct lever for stabilizing rainfall patterns that underpin agriculture, hydropower, and urban water supplies.
Satellite Data and Moisture Tracking
A separate but closely related analysis reinforced these conclusions using an atmospheric moisture-tracking approach and observation-based precipitation datasets covering 1980 to 2019. That research, also released in a Nature journal, found that a large fraction of the observed precipitation decline in the southern Amazon is attributable to deforestation. The southern Amazon has been the epicenter of agricultural expansion and cattle ranching for decades, and this second paper confirmed that the areas with the heaviest forest loss experienced the steepest rainfall drops.
Both studies relied in part on satellite-derived precipitation records. Products such as NASA’s IMERG dataset, which combines data from multiple satellites into a continuous global rainfall record, are now standard tools in Amazon rainfall analyses. Their ability to cover vast, remote areas where ground-based rain gauges are sparse makes them especially valuable for tracking precipitation trends across the basin and for checking whether model-based reconstructions match what is actually happening in the atmosphere.
To separate local and global influences, the researchers also drew on climate-model simulations accessed through an online portal for Nature users. Those simulations allowed them to estimate how much rainfall would have changed in the region if greenhouse gas concentrations had risen as observed but the forest cover had remained intact. Comparing that counterfactual world to the real one highlighted the outsized role of land-use decisions.
The Greenhouse Gas Dimension
While deforestation’s direct effect on rainfall dominated the results, the study also tracked the background greenhouse gas changes that occurred during the study period. The researchers observed an increase of approximately 87 parts per million for CO2 and about 167 parts per billion for CH4 over the timeframe they analyzed, according to coverage of the findings. Those rising concentrations contributed to the 5.2-millimeter share of the rainfall decline attributed to global climate change.
The study also found that deforestation was responsible for 16.5% of the increase in maximum surface air temperature across the study areas. That figure is smaller than the rainfall share because temperature is more strongly influenced by global greenhouse gas forcing. Still, the local warming effect of replacing forest with pasture or cropland adds heat stress to remaining trees, potentially accelerating the cycle of drying and degradation. In cleared landscapes, bare soils and grasses reflect and re-radiate more heat, creating hotter, drier boundary layers that further suppress cloud formation.
Why the Forest Makes Its Own Rain
The mechanism behind these findings is well established in tropical hydrology but often underappreciated in public debate. Amazon trees pull water from deep soil layers and release it through their leaves in a process called evapotranspiration. That moisture rises, forms clouds, and falls again as rain further downwind. By some estimates, more than half of the Amazon basin’s rainfall is recycled water that passed through forest canopy at least once, making the ecosystem a giant biotic pump that draws moist air from the Atlantic and redistributes it across South America.
When trees are removed, this recycling loop weakens. Less moisture enters the atmosphere locally, clouds form less reliably, and dry seasons grow longer and more intense. The primary study quantified this effect with unusual precision, showing that the lost moisture from deforested land accounted for the bulk of the observed drying trend. One of the researchers described the method as a kind of atmospheric bookkeeping that could “separate and weigh each of these components,” turning a complex climate signal into an “account payable” for deforestation that can be directly linked to policy choices.
A Feedback Loop That Could Accelerate
The most concerning implication of the research is the self-reinforcing nature of the cycle it describes. Less rainfall stresses surviving trees, making them more vulnerable to fire and drought-related die-off. That die-off, in turn, reduces evapotranspiration further, cutting rainfall even more. Scientists have long warned that this feedback loop could push parts of the Amazon past a tipping point where forest gives way to degraded savanna, with profoundly different climate and ecological characteristics.
These disturbances, the study’s authors wrote, have far-reaching consequences for the entire Earth system. The Amazon stores enormous quantities of carbon in its biomass and soil. A large-scale transition to savanna would release that carbon into the atmosphere, worsening global warming and reducing the planet’s capacity to absorb future emissions. The regional water cycle disruption would also affect agricultural productivity far beyond the forest itself, since Amazonian moisture feeds rainfall over major farming regions in Brazil, Bolivia, Paraguay, and Argentina.
Implications for Policy and Conservation
The new attribution results arrive amid ongoing debates over how much deforestation the Amazon can withstand before crossing critical thresholds. Earlier work on preserving the forest’s resilience has suggested that large, contiguous tracts of intact canopy are essential to maintaining both regional rainfall and global climate stability. The latest findings sharpen that warning by tying specific amounts of forest loss to measurable declines in dry-season precipitation.
For Brazil and neighboring countries, the message is that local land-use policies can quickly alter regional climate conditions, for better or worse. Expanding protected areas, enforcing existing anti-deforestation laws, and promoting sustainable agriculture on already-cleared land could all help stabilize rainfall. Conversely, if clearing continues near current levels, the studies imply that further drying is not only likely but largely within human control.
As governments negotiate climate commitments and development plans, the research underscores that the Amazon is not just a passive victim of global warming. It is an active component of the climate system whose fate will be determined in significant part by decisions made within its borders. Whether the forest continues to generate its own rain, or slips into a drier, more fire-prone state, now appears less a matter of distant global forces than of immediate choices about how much of it remains standing.
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*This article was researched with the help of AI, with human editors creating the final content.
