A South Atlantic Atmospheric River Dipole Signals Amazon Fire Seasons Months Ahead

Every year, as the dry season descends on the Amazon basin, scientists, firefighters, and policymakers brace for the question that matters most: will this be a bad fire year? The answer has always been elusive, because wildfire activity in the world’s largest rainforest emerges from a tangled web of ocean temperatures, rainfall deficits, land management practices, and chance ignitions. Now a study published in Nature Communications offers a strikingly clear piece of the puzzle. A team of researchers at Tsinghua University has identified a large-scale atmospheric pattern over the South Atlantic Ocean that, appearing in June and July, acts as a powerful precursor to the Amazon wildfires that burn in August and September. The finding could extend the useful lead time for fire forecasting and reshape how scientists think about the chain of events that turns a rainforest into a tinderbox.

The pattern in question is a dipole in atmospheric river activity. Atmospheric rivers are long, narrow corridors of concentrated water vapor transport in the atmosphere, capable of moving enormous quantities of moisture across thousands of kilometers. When they make landfall, they typically deliver intense precipitation, and they are famous for their role in flooding on the west coasts of North America and Europe. But their behavior over the South Atlantic, and their influence on the climate of South America, has received far less attention. The new research, led by Shiyue Zhang, with Wenhao Dong and Deliang Chen as co-authors, shows that the year-to-year arrangement of these moisture corridors over the South Atlantic carries a distinctive fingerprint that is strongly tied to what later happens on the ground in the Amazon.

Specifically, the team identified a June–July dipole mode of South Atlantic atmospheric rivers, characterized by suppressed atmospheric river activity in the northern portion of the basin and enhanced activity in the south. This north-south seesaw is not merely a curiosity of atmospheric circulation statistics. When the dipole is in its characteristic phase, the atmospheric rivers that would ordinarily deliver moisture toward the northern Amazon are weakened or displaced, while moisture transport is concentrated farther south. The result is a large-scale atmospheric setup that starves part of the basin of the precipitation it would otherwise receive during the transition into the dry season.

The consequences of that moisture deficit cascade through the land-atmosphere system in ways the researchers document in detail. Reduced precipitation and lower atmospheric humidity during the critical pre-fire-season months leave soils and vegetation drier than usual. With less cloud cover and less water vapor in the air to intercept incoming energy, surface warming intensifies and solar radiation at the ground increases. Drier, hotter conditions in turn elevate vegetation stress, so that trees and understory plants shed moisture and become more flammable. By the time August and September arrive, the landscape has been primed: fuels are desiccated, the canopy microclimate is hotter and drier, and any ignition source, whether from human activity or lightning, is far more likely to spread into a damaging wildfire.

What makes the study remarkable is the strength of the statistical connection. The researchers estimate that wildfire-related forest loss associated with this atmospheric river dipole mode accounts for approximately 26 percent of the observed interannual variability in total forest loss across the Amazon. In a system where forest loss is influenced by everything from drought and El Niño cycles to road building, agricultural expansion, and enforcement of environmental protections, explaining a quarter of the year-to-year variation with a single atmospheric precursor identified two to three months in advance is a substantial contribution. It suggests that the large-scale moisture circulation over the South Atlantic has been an underappreciated driver of one of the most consequential environmental phenomena on Earth.

The predictive implications are even more striking. Existing seasonal fire forecasts for the Amazon have relied heavily on sea surface temperature anomalies, particularly in the tropical Pacific and Atlantic oceans, observed in May and June, along with wildfire activity already recorded in June and July. These predictors capture part of the signal, but they leave considerable uncertainty. When the researchers added the South Atlantic atmospheric river dipole to a prediction framework built on May–June sea surface temperature anomalies and June–July wildfire activity, the model achieved a coefficient of determination, or R², of 0.67 for August–September burned area. In practical terms, that means roughly two-thirds of the variance in the extent of burned area during the peak fire season can be anticipated before the season begins, a level of skill that could meaningfully improve early-warning systems, resource allocation for firefighting, and policy decisions about land use restrictions in vulnerable regions.

The mechanism behind this predictive power highlights the importance of memory in the climate system. Ocean temperatures in May and June reflect slowly evolving conditions that persist for months, and they help shape the atmospheric circulation that positions and energizes atmospheric rivers. The dipole itself, once established in June and July, sets in motion land-surface changes, drying soils, stressed vegetation, elevated temperatures, that do not reset quickly. By August, the die is largely cast. The atmospheric river dipole therefore serves as an intermediate link in a causal chain that runs from ocean conditions through atmospheric moisture transport to land-surface desiccation and finally to fire. Capturing that intermediate link closes a gap that previous forecasting approaches left open.

Perhaps the most sobering element of the study lies in its look toward the future. Using climate model projections, the researchers find that the South Atlantic atmospheric river dipole mode is expected to intensify under continued warming. A stronger dipole would mean more pronounced suppression of moisture delivery to the northern Amazon in some years, deeper pre-season drying, and more severe vegetation stress when fire season arrives. The implication is that the atmospheric configuration that today explains a quarter of the variability in wildfire-related forest loss could become an even more dominant driver in the decades ahead, amplifying wildfire-driven ecological degradation in a biome that many scientists already consider dangerously close to a tipping point.

The stakes of that projection are difficult to overstate. The Amazon stores vast quantities of carbon, regulates regional and global rainfall patterns, and harbors an extraordinary share of Earth’s terrestrial biodiversity. When its forests burn, carbon is released to the atmosphere, biodiversity is lost, and the degraded landscape becomes more flammable and less resilient, creating feedbacks that can push portions of the forest toward a savanna-like state. Wildfire smoke also degrades air quality across South America, with documented consequences for public health. A forecasting tool that reliably flags high-risk fire seasons months in advance does not prevent fires by itself, but it gives governments, indigenous communities, and conservation organizations time to act, whether by prepositioning firefighting capacity, restricting burning permits, or intensifying surveillance of the most vulnerable landscapes.

The study also underscores how much remains to be learned about atmospheric rivers outside the well-studied mid-latitude domains. The South Atlantic dipole joins a growing body of research showing that these moisture corridors play decisive roles in tropical and subtropical climate variability, and that their behavior is sensitive to the same ocean-atmosphere dynamics, such as sea surface temperature patterns and shifts in the subtropical high, that govern drought and flood risk across the hemisphere. As climate change alters the temperature gradients and circulation features that steer atmospheric rivers, understanding their evolving behavior will be essential not only for the Amazon but for water security and disaster preparedness across South America. For now, the message of this research is direct: the sky over the South Atlantic in early winter may already be writing the script for the Amazon’s fire season, and learning to read it could buy the rainforest precious time.

Subject of Research: A South Atlantic atmospheric river dipole as a precursor of Amazon wildfires and its use in seasonal fire prediction

Article Title: A South Atlantic atmospheric river dipole as a key precursor of Amazon wildfires

Article References: A South Atlantic atmospheric river dipole as a key precursor of Amazon wildfires. (n.d.). https://doi.org/10.1038/s41467-026-78572-z

Image Credits: AI Generated

DOI: 10.1038/s41467-026-78572-z

Keywords: atmospheric rivers, Amazon wildfires, South Atlantic, seasonal forecasting, forest loss, land-atmosphere feedback, climate change, fire ecology, vegetation stress, sea surface temperature, Nature Communications, dipole mode