Brazil is expected to face at least six heat waves by the end of the year, driven by an El Niño that may become one of the strongest on record. The forecast comes from an analysis by the National Center for Monitoring and Early Warning of Natural Disasters (Cemaden), a federal agency, based on 47 years of temperature records. The number could be higher: during the last El Niño, in 2023 and 2024, the country endured nine heat waves between August and December, the most since records began in 1979 and more than double the national average of four events.
Under the study's criteria, a heat wave occurs when, for at least three consecutive days, both daytime highs and nighttime lows stay exceptionally above normal, with no relief even at night. "That is an average, but in the last El Niño we saw the country live through nine heat waves, with extremely hot days," researcher Mabel Calim Costa, who holds a doctorate in Earth system science and authored the survey at Cemaden, told G1. "With ocean temperatures rising, the scenario could be even more intense, and that brings consequences for the country."
More frequent and more widespread
The study points to a shift in how extreme heat behaves across Brazil. In the 1980s and 1990s, episodes were rare and concentrated in specific regions, such as the Northeast. From 2010 onward, and more sharply after 2020, heat waves became more frequent and began covering the whole country at the same time. "The heat wave now affects the entire country, and that is an issue because we are talking about additional heat in areas that are already hot and in areas that have no resilience to face such high temperatures," Mabel said. In 2024, more than 6 million Brazilians faced at least 150 days of extreme heat, according to a G1 survey.
The expected intensity originates in the equatorial Pacific. The current El Niño was officially declared in June and has strengthened quickly. According to MetSul, a Brazilian weather service, the model run by the Met Office, the United Kingdom's national weather service, projects temperatures more than 3°C above average in the Pacific's Niño 3.4 region, a level that would place the episode in the Super El Niño category and make it surpass the major events of 1982-1983, 1997-1998 and 2015-2016. The British service also estimates that 2027 could overtake 2024 as the hottest year ever measured on the planet.
The immediate trigger for the waves is usually the formation of high-pressure areas that stall over a region for several days, blocking clouds and rain and trapping a mass of hot, dry air in place. Without rain, soil moisture is depleted, which intensifies warming and can worsen existing drought. On a hotter planet, each such episode produces more extreme peaks than it would have decades ago. For September, forecast maps already show nearly all of Brazil in orange and red tones, with temperatures that could reach 3°C above average, according to G1.
Severe drought in 157 cities
The heat tends to aggravate drought. According to the Integrated Drought Index, produced by Cemaden for the federal government, 157 cities are already in severe drought, most of them in the North and Northeast. Tocantins accounts for 50 municipalities in that condition, and Bahia for 18. "The most affected regions will be the North and the Northeast, we are already seeing rainfall below what was expected in those regions," said Ana Paula Cunha, a drought specialist at Cemaden.
Fire risk is also rising. A joint survey by CPTEC/Inpe, the national weather and climate forecasting center, the Inmet meteorology institute and Funceme, Ceara's state meteorology foundation, classifies Brazilian municipalities by fire risk level, combining data on human activity with heat-spot trends. Together with the alerts issued by Cemaden, this monitoring is now the basis for states and municipalities to prepare for the extreme heat, drought and wildfire episodes that El Niño is expected to intensify in the coming months.