Brazil is increasingly affected by extreme weather events due to climate change, with pronounced regional differences in temperature and precipitation patterns. The southeast region is particularly vulnerable, frequently experiencing severe droughts and extreme heatwaves linked to atmospheric blocking events and intense rainfall episodes driven by the South Atlantic Convergence Zone (SACZ). These phenomena contribute to recurring climate-related disasters. The country’s heavy reliance on hydropower heightens its susceptibility to droughts, while growing evidence points to intensifying dry spells and wildfires across multiple regions, threatening agricultural output and food security. Urban areas, particularly, are experiencing more frequent and severe heatwaves, posing serious health risks to vulnerable populations. This study investigates the links between global teleconnection indices and synoptic-scale systems, specifically blocking events and SACZ activity, and their influence on Brazil’s extreme heat, drought conditions, and river flow variability over the past 30 to 40 years. By clarifying these interactions, the research aims to enhance understanding of how large-scale atmospheric dynamics shape climate extremes and to assess their broader implications for water resource management, energy production, and regional climate variability.

The South Atlantic Convergence Zone (SACZ) is an atmospheric phenomenon typical of summertime where a band of nebulosity causes intense or persistent rainfall in many regions of Brazil. SACZ episodes can be responsible for many natural disasters. Besides, the impacts of rainfall on water availability and consequently on the energy sector are extensive. The main objective of this study was to investigate the implementation of the SACZ index as an objective forecasting tool using input data from the Global Forecast System (GFS) model. Initially, we compared the index with the SACZ events identified by the Center for Weather Forecasting and Climate Studies (CPTEC ) from 2017 to 2021. Results showed that the index represented all events identified SACZs by CPTEC. Finally, we used data from the GFS 0.25 Degree from 2017 to 2021 to calculate Accuracy, Probability of detection, and False alarm ratio to evaluate the SACZ index as a prediction tool. Three thresholds are defined for the binary classification of a possible SACZ event. Results showed that above the most sensitive threshold (h1), within 10 days in advance, the sign of a possible SACZ can be detected. For the intermediate threshold (h2), a forecast of 96 h can detect a sign. For the most specific threshold (h3), the index can detect the event within 72 h in advance with a probability of detection of almost 90%. The SACZ index proved to be an efficient tool for detecting the dynamics of the phenomenon and can be used to assist operationally and in decision-making.

The increase of heatwaves has been observed due to the influence of a changing climate on the planet. Among populations, this phenomenon is associated with a rise in various types of cardiovascular diseases, particularly among vulnerable groups such as the elderly and individuals with pre-existing conditions. This presents a growing concern for healthcare systems and urban management. Although the literature predominantly highlights these events on the European continent, it is known that heatwaves are not confined to this region. Thus, the objective of this study is to evaluate the temporal evolution of the phenomenon through an index developed by LAMMOC/UFF to detect extreme heatwaves in the 26 Brazilian capitals and the Federal District. For this purpose, ERA5 reanalysis data from January 1950 to September 2024 were utilized. The index was calculated hourly and aggregated on a daily and monthly basis. Initially, the Mann-Kendall test was employed to assess the trends in the time series. It was observed that 19 of the analyzed cities exhibited a positive trend, two showed no trend (Florianópolis and Fortaleza), and six coastal cities (primarily in northeastern region, except for Teresina and Recife) located in a region with barotropic conditions did not show occurrences of extreme heat waves during the study period. Subsequently, a correlation matrix between the time series was analyzed, along with clustering, identifying three distinct groups: one less affected by extreme heat waves, a second intermediate group with a positive trend, and a third group that exhibited the most significant positive trends. The time series were then divided, applying a clustering technique, into three distinct periods: 1950–1974 (P1), 1975–1999 (P2), and 2000–2024 (P3). This allowed the calculation of the average accumulated values for these three periods across all evaluated cities to observe the percentage differences. For instance, from P1 to P3, in the southeastern region, the cities of Rio de Janeiro and São Paulo presented an approximate 613% and 643% increase in extreme heatwave occurrences, while in the south region, Porto Alegre had an increase of 557%. In the midwest, Campo Grande and Cuiabá presented an increase of 983% and 671% and in the northeast Recife and Teresina presented an increase of 217% and 257%. Furthermore, the third cluster displayed the highest trends and averages, encompassing most cities of the Northern region. Therefore, cities such as Macapá, Rio Branco, Manaus and Belém experienced an increase of 3154%, 1339%, 1100% and 1028%, respectively. Notably, it was observed that this third cluster predominantly comprised cities in the northern region of the country, situated within the Amazon biome. These findings call for further investigation into the relationship between this trend and factors such as increasing deforestation and forest fires in the region. These alarming results highlight the urgent challenges in environmental, healthcare, and urban management driven by climate change and extreme events, emphasizing the need for investments in municipal health, resilience, and climate mitigation and adaptation strategies.

The South Atlantic Convergence Zone (SACZ) is one of the most important phenomena that influences the precipitation patterns in Brazil’s Southeast and Midwest regions during the spring and summer. These regions play a major role for the country’s economy, particularly in terms of agriculture and industrial production. It is estimated that the SACZ is responsible for approximately 25% of the total volume of rain in Southeast Brazil from October to April. The conditional probability of a natural disaster occurring when the SACZ is present in the region is around 24%, while, in the case of a disaster occurring in the Southeast, the conditional probability of observing the presence of SACZ is 48%. This work provides an initial understanding of how different teleconnection patterns can influence the configuration, position, and intensity of the SACZ. The goal is to investigate potential correlations between the SACZ index, the El Niño Southern Oscillation (ENSO) indexes, the Atlantic Sea surface temperatures (SST) between Central America and Africa, the Brazil-Malvinas Confluence (BMC) and the Antarctic Oscillation (AAO). For the SACZ indexes, the monthly data was derived by summing the values for each month. This process utilized data spanning from 1980 to 2010 to establish the monthly climatology. The monthly indexes and anomalies were compared with the monthly climatology values from January 1999 to December 2022. For daily indexes of BMC, Niño1+2, Niño 3, Niño 3.4, Niño 4, Atl_N, Atl_NL, Atl_C and Atl_CL sea surface temperature (SST) anomalies were referenced against a climatology spanning from 1971 to 2000. In these cases, monthly data was obtained through the average of the daily indexes. Finally, AAO indexes were already obtained monthly. In this case, the time series were normalized using the standard deviation of the monthly index, based on the 1979-2000 period. Three Pearson correlations were calculated monthly for the period from 1999 to 2022. These correlations were evaluated for the average from October to March, October to December, and from January to March. The preliminary results showed that colder anomalies of the Equatorial Pacific (La Niña), the North Equatorial Atlantic, and the CBM, in conjunction with a positive phase of the AAO and warmer waters of the Central Equatorial Atlantic, are associated with the occurrence and configuration of the SACZ (and vice versa). This signal is most pronounced in the period from October to December and during the October to March timeframe, while it weakens in the months from January to March.

Climate change is disrupting atmospheric patterns, which, in turn, alters precipitation regimes worldwide. Droughts are becoming more frequent, intense, prolonged, and spatially distributed, posing a threat to water security for millions of people. Drought monitoring is particularly critical in Brazil, a country that encompasses diverse climate regimes and biomes, and where rainfall variability greatly impacts social vulnerabilities, biodiversity, and the economy. To better understand disruptions in rainfall patterns leading to drier conditions in Brazil, we evaluated the correlation between the occurrence of atmospheric blockings and episodes of the South Atlantic Convergence Zone (SACZ) with rainfall variability, particularly for droughts, in various biomes. The Standardized Precipitation Index (SPI) was used to characterize precipitation variability, presenting simple yet robust statistical insights into the distribution, duration and frequency of rainfalls surpluses (positive values) and droughts (negative values). The SPI values for 1, 6 and 12 months were calculated using observed rainfall data from the Brazilian Daily Weather Gridded Data (BR-DWGD) database, from 1961 to 2024. SACZ episodes and atmospheric blocking events were identified using indices developed by LAMMOC/UFF research group, which effectively describe the behaviour of these systems across various regions of the country. The atmospheric blocking index was calculated using ERA5 reanalysis data, while NCEP reanalysis data was the input to the SACZ index. All data were normalized prior to statistical analyses, which included Pearson’s correlation coefficient, Principal Component Analysis (PCA), K-means clustering, Mann-Kendall test, and trend analysis to identify and quantify trends. The results demonstrate that atmospheric blocking events are increasing in all regions of Brazil. Conversely, the SACZ occurrences did not demonstrate a significant trend. The correlation between atmospheric blockings and SPI values exhibit a strong pattern in all evaluated time scales and regions, demonstrating significant positive influence in the Pampa biome within all evaluated time scales, suggesting that blockings, regardless of their position, incur in rainfall surpluses in South Brazil. In the other biomes, blockings show a consistent negative influence, particularly in Cerrado, Pantanal and Amazonia (Central and Northern regions). Cerrado shows correlations of up to -0.5, the highest values observed in the analysis - suggesting atmospheric blockings have an inhibiting effect in precipitation, creating drier conditions that are concerning for wildfire hazard in central Brazil, and also in Southern Amazonia. SACZ and SPI correlation is not as clear, with small to no trend in most biomes, except for the slight negative influence on the Pampa, region where precipitation decreases as active SACZs concentrate rainfall northward. Understanding the correlation between these important atmospheric systems and the precipitation variability observed in Brazil is valuable to drought monitoring and prediction, and may help to identify early warning signals for major droughts, providing insights that can guide mitigation and adaptation strategies to address the impacts of climate change, which affects differently the regions of the country due to the complexity of its diverse climate regimes and biomes, and therefore, water availability and wildfire hazard.