Impacts of Atmospheric Phenomena on River Flow and Hydropower Stability in Brazil

Renewable energy sources are inherently influenced by environmental variability. In Brazil, hydropower constitutes approximately 65% of the country’s electricity matrix, relying directly on river flow, which is strongly governed by precipitation on an operational timescale. This study investigates the influence of atmospheric blocking events and episodes of the South Atlantic Convergence Zone (SACZ) on the occurrence and magnitude of natural flow in several hydropower plants in river basins across Brazil. Atmospheric blocking and SACZ episodes were characterized using indices developed at LAMMOC/UFF, which effectively capture the behavior of these systems in different regions of the country. The SACZ index was calculated using NCEP reanalysis data, while the blocking index was derived from ERA5 reanalysis data. Natural flow data for the power plant areas were provided by the National Electric System Operator (ONS). To maximize the availability of records for this study, the time series was defined from 1960 to 2023. All data were normalized for statistical analyses, and methods such as Pearson’s correlation coefficient, Principal Component Analysis (PCA), K-means clustering, trend analysis, and the Mann-Kendall test were employed to identify and quantify trends. Results indicate that blocking events have shown a rising trend across all evaluated regions, whereas SACZ episodes do not display an increasing trend uniformly throughout the country. Regarding river flow trends, increases were observed in Southern Brazil, while decreases predominate in the Southeast, Central-West, Northeast, and North regions. SACZ episodes positively influence flow in hydropower plants in the Central-West, North, and Northeast regions, while inhibiting precipitation in the South as their effects shift northward, away from the basins. For instance, the Paranaíba River basin in the Northeast shows a correlation of 0.55 with SACZ episodes, and the Paraopeba River basin located between the Southeast and Central-West Regions, presents a correlation of 0.57. Notable SACZ-related correlations are also observed in the Grande, Paranaíba, and Baixo Paraná basins, with values exceeding 0.3 and increasing towards the South, reaching over 0.5 for Baixo Paraná and 0.6 for Grande and Paranaíba basins. Conversely, the Araguaia-Tocantins basin in the North exhibits one of the highest correlations, at 0.69. Atmospheric blocking events, in turn, are positively correlated with river flow in the South, particularly in the Uruguai and Jacuí basins, which exhibit the highest correlation values. However, they produce a negative correlation in basins of other regions, as their associated high-pressure systems inhibit atmospheric dynamics, reduce precipitation, and prevent the advance of cold fronts, concentrating precipitation in Southern areas. The results reveal a decline in river flow across most hydropower plant areas, posing risks to Brazil’s electricity production, with potential impacts on the country’s Gross Domestic Product (GPD). SACZ and atmospheric blocking events significantly influence river flow, especially in the power plants of the Central-West, North, and Northeast regions. Developing indices for these atmospheric phenomena offers valuable insights into regional water availability, supporting strategies to mitigate risks from shifting precipitation regimes across Brazil’s diverse climates and biomes.