Characterisation of the Exceptional Heatwave Conditions Observed in Brazil During the Record‐Hot Years of 2024 and 2025

Abstract

The intense heatwaves of 2024 and the summer of 2025 underscored Brazil's vulnerability to climate change and extreme weather events. Our results show that 2024 recorded a higher number of hot spells, particularly in subtropical Brazil, while in 2023 the intensity of heatwaves was greater. During the summer of 2025, air temperatures in large parts of southern Brazil exceeded 40°C, reflecting the extreme heatwave conditions in that region. Between 1979 and the austral summer of 2025, there was a notable increase in both the number and intensity of heatwaves in tropical and subtropical regions of Brazil. Areas that rarely experienced heatwaves in the 1980s, such as the Amazon and northeastern Brazil, have been facing increasingly severe heatwave conditions since the 2000s. Significant differences were observed in the spatial extent and intensity of exceptional warm temperatures across the case studies in 2024 and in 2025, when Northern and central Brazil were the most severely affected regions. Co‐occurring drought conditions in 2024 likely heightened sensible and heat fluxes from the drying soil to the atmosphere, further escalating temperatures during the heatwave episodes. As a result, there was a significant increase in wildfire risk and activity, especially in June and September 2024. In contrast, during the summer of 2025, the central‐eastern and particularly southern regions of the country experienced the highest temperatures and the longest heatwaves.

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