The Role of Teleconnection Indices in Modulating Rainfall and Drought in Central Brazil

Increasing temperatures due to climate change pose challenges to countries worldwide, including Brazil, where extreme weather may result in biodiversity loss, water resource availability changes, and significant economic and health impacts. This study evaluates the influence of various teleconnection indices on the variability patterns of atmospheric blocking events occurring in central Brazil and episodes of the South Atlantic Convergence Zone (SACZ). Nearly all teleconnection indices made available in the NOAA’s website were analysed, including those related to the Pacific, Atlantic, Indian Oceans and global-scale indices. Additionally, four new indices were explicitly developed for this study, focusing on NOAA’s OISST Sea Surface Temperature anomalies in the North Atlantic Ocean near the Moroccan coast. The characterization of atmospheric blocking events and SACZ episodes was carried out using indices developed at LAMMOC/UFF, which effectively capture the behaviour of these atmospheric systems across different regions of Brazil. The SACZ index was calculated using NCEP Reanalysis data, while the atmospheric blocking index used ERA5 reanalysis data, resulting in a time series spanning from 1981 to 2023. All data were normalized for statistical analyses, and methods including Pearson’s correlation coefficient, Principal Component Analysis, K-means clustering techniques, trend analysis, and the Mann-Kendall test were applied to identify and quantify trends in the data. Atmospheric blocking and SACZ episodes have contrasting yet significant influences on the rainfall in central Brazil. Atmospheric blocking events are typically associated with prolonged droughts, whereas SACZ episodes are linked to intense and spatially well-distributed precipitation. This region is vital for the country’s agriculture, industry, and energy production. The analysis revealed that a significant portion of oceanic indices from the Atlantic and the Pacific Oceans, along with atmospheric blocking events, exhibit strong increasing trends. These trends are accompanied by positive correlations, observed in the trend-inclusive and detrended series. For instance, correlations reach 0.7 values with the Global Mean Land/Ocean Temperature, 0.45 with ENSO indices, 0.55 with North Atlantic indices near the Moroccan coast, and 0.67 with the Pacific Warmpool Area Average. In contrast, the SACZ index showed no clear trend in the Mann-Kendall tests. Correlations between SACZ and the same oceanic indices often exhibited an inverse relationship compared to those with blocking indices and were also generally weaker, ranging between -0.15 and -0.30. One exception was a positive correlation of around 0.34 with the East Pacific/North Pacific Oscillation index. Overall, the study highlights that atmospheric blocking events are becoming increasingly frequent and intense in central Brazil, closely following the warming trend of the oceans. This poses a warning for the region’s hydrometeorological regime. While the absence of an evident decline in SACZ episodes provides some relief, the escalating deforestation in the Amazon, one of the primary sources of moisture driving precipitation during SACZ episodes, may become the decisive factor in altering the region’s precipitation patterns, potentially exacerbating the ongoing water crisis in central Brazil.