Heat and Cold Waves in Brazil: An <scp>ERA5</scp> ‐Based Analysis of Trends and Seasonality (1980–2024)

ABSTRACT Anthropogenic warming intensifies heatwaves and simultaneously diminishes coldwave frequency and severity. In Brazil, while recent reanalysis‐based studies have improved the understanding of heat extremes, nationwide assessments of both heat and cold waves using reanalysis data remain scarce. This study analyzes long‐term trends in climate types, as well as in extreme temperature events using ERA5 reanalysis data (1980–2024), spanning 11,314 grid points across Brazil using apparent temperature as a metric. Extreme heat days (EHDs), extreme cold days (ECDs), and multi‐day heatwave and coldwave events were defined using the 95th and 5th percentile thresholds of temperature distributions. Temporal trends in frequency and seasonality were evaluated using linear regression and Theil–Sen estimators. Results indicate an average national warming of 0.89°C since 1980, with stronger warming (~1°C) in northern regions and weaker increases (~0.6°C) in the South. EHDs have intensified across the Amazon, Northeast interior, and Midwest, while ECDs have decreased nationwide, aside from isolated cold anomalies in the early 2020s. Heatwaves have become markedly more frequent, especially in low‐elevation and continental interior areas. Coldwaves show a widespread decline but exhibit a modest resurgence in parts of the Central Plateau during the 2020s. Seasonal analyses reveal that EHDs peak from August to October in interior regions, whereas ECDs cluster in July, closely associated with polar incursions. A key contribution of this study is the systematic analysis of the seasonality, onset timing, and long‐term evolution of extreme heat and cold events across Köppen–Geiger climate types, and all states in Brazil. Moreover, high‐resolution spatial and seasonal characterisation of extreme temperature trends further identifies regions increasingly vulnerable to heat and cold extremes, supporting improvements in early‐warning systems and climate adaptation planning.