While El Niño is known for its far-reaching global impacts, the regions closest to the warming waters of the equatorial Pacific—particularly South America—often bear the immediate and most severe brunt of the phenomenon. "Activity here is frenetic due to the intense El Niño event," says Alice Grimm, a professor at the Federal University of Paraná in Curitiba, Brazil, and author of a study published on November 12 in Atmospheric and Oceanic Science Letters .
That brunt is unusually heavy because of what is at stake. Across much of South America, energy generation, agriculture, livestock, and fisheries remain closely tied to rainfall timing, and a large share of the population depends on these climate-sensitive livelihoods, often with limited capacity to absorb shocks. The Economic Commission for Latin America and the Caribbean has warned that an extreme El Niño could cost the region at least 2% of GDP over three years and push as many as 4.8 million more people into poverty . When rain arrives too hard, too fast, or not at all, the consequences move quickly from fields to food prices, from rivers to displaced families.
South America has already felt this harsh reality. In November 2023, rivers in Rio do Sul, South Brazil, exceeded 13 meters—9 meters above normal levels—submerging half the urban area and displacing 18,000 people .
This devastating event highlights a critical gap in how El Niño preparedness is typically framed. "Previous studies highlight the seasonal variations of El Niño's impact. However, seasonal averages fail to capture the intense, abrupt fluctuations revealed in our research," Grimm explains. "This paper presents a month-by-month evolution."
To achieve that resolution, Grimm compiled a 75-year observational dataset covering 15 distinct El Niño events, drawn from more than 10,000 rain gauge stations across the continent and verified over nearly a year. The findings reveal a stark and opposing continental divide: while the northern Amazon experiences severe drought, the subtropical belt—especially Southern Brazil—faces torrential rainfall. These swings are driven by tropical and extratropical teleconnections that depend on evolving anomalous sea surface temperatures, varying background oceanic and atmospheric states and even surface–atmosphere interactions that can rapidly reorganize regional circulation and moisture transport.
The study also uses "Influence Functions" to identify the key atmospheric source regions driving these remote impacts. Monitoring those regions, Grimm suggests, can help anticipate how intense an El Niño's effects on South America are likely to be.
"The findings indicate the months and regions most likely to experience the most intense precipitation impacts during an El Niño event, enabling more targeted, focused, and efficient preparedness," she notes. That message has already resonated beyond the lab: since July, Grimm has delivered more than ten lectures to municipal governments, civil defense agencies, and universities. Even at what is usually a milder stage in the beginning of the event, since July, the 2026 El Niño has already driven 1,035 Brazilian municipalities to suffer severe impacts related to the climate phenomenon, according to the consolidated survey by the National Confederation of Municipalities (CNM) and the National Civil Defense. The vast majority of these cities have declared a state of emergency to gain access to federal relief and reconstruction funds. The repercussions of the El Niño manifested in opposite ways across different regions of the country: extreme droughts and dry spells concentrated mainly in the North and Northeast regions; intense rains and flooding focused especially in the South region. In total, it is estimated that more than 7 million Brazilians have been directly affected by the impacts of these climate anomalies between July and October 2026 .
Grimm emphasizes, however, that the analysis describes a statistically consistent average behavior, not a fixed script. Individual El Niño events can deviate from the historical baseline, so vigilance remains necessary. Her next goal is to move beyond average rainfall anomalies and examine how El Niño changes the frequency of extreme events themselves. "Since these extreme events cause disasters and the greatest economic and social damages," she says, "it is critical to indicate when and where they become more frequent, thereby reducing exposure and vulnerability."
For a region where rainfall is both a lifeline and a threat, knowing in greater detail when and where the greatest impacts of El Niño are most likely to occur is a first step toward protecting lives and livelihoods.
