Variabilidade hidroclimática da bacia do Rio Negro e a influência da Zona de Convergência Intertropical do Atlântico

Abstract

This study investigates the hydroclimatic variability of the Rio Negro Basin, articulating the influence of the ITCZ ​​and ocean-atmospheric teleconnections on precipitation and regional hydrological dynamics. The objective was to determine long-term changes in hydrometeorological variability and quantify the role of the ITCZ ​​in the rainfall regime of the Rio Negro. Historical series of precipitation, level and flow (with emphasis on the level in Manaus since 1902) and climatic indices (SOI, PDO and ADI) were used, the Mann-Kendall test and Sen's slope were applied, spectral analyses (Fourier and wavelet) and dynamic/convective diagnostics with ERA5 and OLR were performed. The results indicate a positive trend in the river level in Manaus of approximately 0.9 m over 122 years, reinforced by daily and five-year data. Between 1973–2024, annual floods increased (~0.012 m year⁻¹) and droughts decreased (~−3.57 m), increasing the annual amplitude by ~4.18 m. The spectra show the dominance of annual and semi-annual cycles and multi-year (3–6 years, associated with ENSO) and quasi-decadal (~16 years) variability, with strengthening of these signals in the recent period; there is evidence of regime change from the late 1970s/early 1980s. The average precipitation of the basin does not show a significant linear trend in the analyzed period, although the ITCZ ​​explains a substantial part of its variability (significant and negative correlation between ITCZ ​​intensity and average basin rainfall), while no significant correlation with the PDO is observed; in some sub-basins there are indications of partial level-runoff decoupling. It is concluded that the seasonal intensification and increased frequency of recent extremes impose growing hydrological risks; adaptive management actions are recommended, along with the combined use of seasonal forecasts and continuous monitoring based on the relationships between the ITCZ, precipitation, and hydrological response.