Analysis of Climate Variability of Homogeneous Regions of Rainfall Anomalies in Southeast South America ( <scp>SESA</scp> )

ABSTRACT Rainfall variability in Southeastern South America (SESA) is influenced by local, regional, and global factors, as well as complex interactions between the Pacific and Atlantic Oceans. This study aims to characterise the monthly variability and cyclicity of the time series for six Homogeneous Regions of Rainfall Anomalies (HRRA) in SESA from 1961 to 2020 and analyse the climatic variability of precipitation in these regions. Monthly rainfall data from the Climatic Research Unit were used. The six HRRA are located between 32°–40° S (regions 1–2), 24°–32° S (HRRA‐3–4), and 20°–27° S (regions 5–6). Time series for each HRRA were calculated based on the average of its four central points. Boxplots of monthly totals were created, and the Standard Normal Homogeneity Test (SNHT) and Wavelet Transform (WT) were applied to the anomaly series. Results indicate that HRRA‐1, 2, 4, 5, and 6 are influenced by regional circulation, with dry/rainy periods in winter/summer. HRRA‐4–6 show climatological features typical of the monsoon, while HRRA‐3 exhibits variability without a dominant dry or rainy season. Boxplots reveal greater variability in spring, summer, and fall. SNHT detected structural breaks in 1972, 1976, 2000, 2009, and 2019, corresponding to HRRA‐1, 4, 2, 6, 3, and 5, respectively. WT analysis revealed significant influences in seasonal, interannual, and interdecadal cycles across all regions. Seasonal variability predominates in HRRAs‐1, 4, and 6, while interannual variability, linked to ENSO, SAM, and PSA, dominates in HRRAs‐2, 3, and 5. Interdecadal cycles were observed in HRRAs‐1, 2, 3, and 5, suggesting PDO influence.