Rethinking heatwave analysis under climate change: A climatic-type approach across Brazil

This study analyzes the spatial and temporal variability of heatwaves in Brazil based on Köppen climate classification, rather than administrative boundaries, over the period 1991–2020. It focuses on key heatwave characteristics, including frequency, intensity, and duration, while also examining seasonality and long-term trends across eight climate types. This approach contributes to a more nuanced understanding of how extreme heat events manifest under different atmospheric regimes. Daily maximum temperature data from the Instituto Nacional de Meteorologia (INMET) were used to calculate the Warm Spell Duration Index (WSDI), with heatwaves defined as periods of at least six consecutive days exceeding the climatological 90th percentile. Data processing involved gap-filling techniques and automated workflows implemented through HEATpulse, an R package designed for heatwave detection. The results reveal 1) A consistent intensification of heat extremes, particularly after 2010. 2) A seasonal expansion of heatwaves was identified, with events extending beyond the traditional dry season in the Amazon and becoming more persistent in Equatorial Savanna climates—specifically the As (summer dry) and Aw (winter dry) types—where monthly frequencies exceeded 15 and 21 days, respectively. 3) Heatwave occurrences have also surpassed typical seasonal boundaries in other climates, including Aw regimes. 4) Statistically significant positive trends ( p < 0.05) were primarily observed in tropical and semi-arid climates, indicating that extreme heat has transitioned from episodic occurrences to a structural characteristic of these regions. The findings highlight Equatorial Monsoon (Am), Equatorial Savanna (As), and Equatorial Savanna (Aw) climates as particularly vulnerable. Applying this framework, these patterns may also be relevant to analogous regions globally, including Central Africa, southern and eastern India, mainland Southeast Asia, and northern Australia, which are susceptible to heatwaves.