Long-term basin trends confirm a record 2022–2024 hydrological drought and water-storage losses in western Amazonia

Western Amazonia, including the Peruvian and Ecuadorian Amazon-Andes transition zone, within the contributing basin of the Tamshiyacu hydrological station near the Marañón–Ucayali confluence, contributing ∼16 % of Amazon discharge (32,000 m³ s⁻¹). This study follows a three-part methodology: (i) establishing a long-term historical baseline by evaluating trends in precipitation (1981–2024), runoff (1984–2024), and high-runoff season timing (1984–2024); (ii) characterizing recent rainfall anomalies in the 2022–2024 period; and (iii) diagnosing the 2022–2024 drought's hydrological impacts using standardized indices (SRI) and water storage anomalies. This study first establishes critical long-term (1981–2024) trends, revealing a significant delay in the onset of the high-runoff season (12 days/decade) and a significant decrease in low-flow season discharge (−116.3 m³ s⁻¹ yr⁻¹). This trend analysis provided the necessary historical context, revealing long-term vulnerability that was exacerbated by the 2022–2024 drought, driven by persistent precipitation deficits. The drought's impacts were unprecedented: the drought lasted a record 24 months (SRI-6), TWS anomalies reached their lowest level on record (below −15 cm), and discharge collapsed below 10,000 m³ s⁻¹ by August 2024. These findings underscore the region's growing vulnerability and the urgent need for adaptive water resource management. • The 2022–2024 Amazon drought lasted 24 months, the longest on record. • High-runoff season onset delayed by 12 days per decade from 1984 to 2024. • Terrestrial and groundwater storage showed depletion, worsening water scarcity.