The Tropical Atlantic as an Antecedent Indicator of the Magnitude of Hydrological Droughts in the Western Amazon: Evidence from Coari and Regional Validation

This study investigated the association between Tropical Atlantic climate indicators and the magnitude of hydrological droughts in Coari (AM), using the minimum stage of the Solimões River between August and November as the response variable. Thirty-three years (1982–2024) and 168 candidate variables were analyzed with rigorous statistical controls (Bonferroni, FDR, partial correlations, cross-validation, Monte Carlo). The TNA_Jun index showed the best performance (R² = 0.555), substantially outperforming the best ENSO indicator (Niño3.4_Feb; R² = 0.091), with partial correlations of −0.72 even after controlling for ENSO. Spatial consistency was confirmed across 19 Amazonian gauging stations and in the Tocantins–Araguaia Basin. It is concluded that the thermal variability of the Tropical North Atlantic allows the intensity of the annual low-water season to be anticipated approximately four months in advance, with potential applications in hydrological risk management and regional logistics planning. (2026-07-16)