Influence of Atmospheric Blocking and SACZ Episodes on Extreme Heatwaves in Brazil: A Long-Term Analysis

Rising temperatures driven by climate change pose significant challenges worldwide. In Brazil, these challenges include extreme weather events such as heatwaves, which can have severe health impacts. This study investigates the influence of atmospheric blocking events and episodes of the South Atlantic Convergence Zone (SACZ) on Brazil's occurrence and intensity of extreme heatwaves. Atmospheric blocking and SACZ episodes were characterized using indices developed at LAMMOC/UFF, which effectively capture the behavior of these systems across different regions of the country. Atmospheric blocking events are typically associated with prolonged droughts, while SACZ episodes are linked to intense, spatially well-distributed precipitation. The newly developed Extreme Heatwave (XHW) index was applied in this study due to its global applicability, covering all 26 state capitals and the Federal District of Brazil. The SACZ index was calculated using NCEP Reanalysis data (I and II) while blocking and XHW indices were calculated using ERA5 reanalysis data, generating a time series from 1960 to 2024. To facilitate statistical analyses, all data were normalized. Methods such as Pearson’s correlation coefficient, Principal Component Analysis (PCA), K-means clustering, trend analysis, and the Mann-Kendall test were applied to identify and quantify trends in the series. The results showed an increase in extreme heat events in most cities, except for Florianópolis (in the South) and Fortaleza (in the Northeast), which displayed no significant trend. Atmospheric blockings also showed a clearer upward trend across all evaluated regions compared to SACZ episodes. The correlation between the SACZ and heatwaves is statistically insignificant across most of Brazil, with values close to zero, as the SACZ is not associated with significant temperature gradients, causing little to no impact on the occurrence of heatwaves. In contrast, atmospheric blockings show statistically significant positive correlations with heatwaves, particularly in geographically specific regions. For example, in the North region, Palmas (TO) stands out with a correlation of 0.44, while Manaus (AM) approaches a value of 0.38. These cities are more responsive to northern-located blockings. Rio de Janeiro (RJ), in the Southeast, and Cuiabá (MT), in the Central-West, exhibit a correlation of 0.37 due to southern and northern-located blockings, respectively. In the South, Porto Alegre (RS) is the most responsive to southern-located blockings with a correlation of 0.18. In the Northeast, values are generally low, with Recife (PE) showing the highest correlation (0.16) for northern-located blockings. This study emphasizes the importance of spatial analysis in understanding the influence of atmospheric blockings on extreme heatwaves events, revealing a direct relationship between the position of blockings and their impact, as evidenced by the varying responses of different cities. As atmospheric blockings increase in frequency due to climate change, heatwaves are also expected to become more frequent and intense. This trend poses a growing risk to public health and mortality, as well as significant challenges to the healthcare system.