Understanding Paraguay River hydrology to support sustainable management of the world's largest tropical wetland

The Paraguay River is the main hydrological axis of the Pantanal wetland, the world’s largest tropical floodplain, and plays a key role in the hydrodynamics and ecological functioning of the Upper Paraguay Basin (UPB). This study evaluated the spatio-temporal variability of river levels at six fluviometric stations distributed along the Paraguay River and adjacent sectors of the UPB: Cáceres, Cuiabá, Bela Vista do Norte, Ladário, Forte Coimbra, and Porto Murtinho. Daily water-level data provided by the Brazilian Navy (CHN-6) were used for descriptive, persistence, multivariate, spectral, duration-curve, heatmap, anomaly, and clustering analyses. Long-term trends were evaluated using annual water-level series and the Mann–Kendall test after trend-free pre-whitening (TFPW) to account for serial dependence, with Sen's slope used to quantify the magnitude of change. The results revealed pronounced hydrological seasonality associated with the annual Pantanal flood pulse and strong temporal persistence throughout the series. Bela Vista do Norte exhibited the greatest hydrological stability, whereas Porto Murtinho showed the highest hydrological amplitude and strongest influence of accumulated upstream flows. After accounting for serial dependence using trend-free pre-whitening, significant long-term decreases in annual river stage were detected at Cáceres and Cuiabá, with Sen's slopes of −0.0234 and −0.0191 m year⁻¹, respectively. In contrast, no statistically significant monotonic trends were detected at Bela Vista do Norte, Ladário, Forte Coimbra, or Porto Murtinho. PCA and cluster analysis indicated strong similarity between Cáceres and Cuiabá, whereas Porto Murtinho displayed more independent behavior. Spectral and Singular Spectrum Analysis (SSA) analyses highlighted the dominance of low-frequency seasonal oscillations. These findings improve understanding of Pantanal hydrodynamics and provide valuable information for water resources management, environmental monitoring, and climate adaptation strategies in the Upper Paraguay Basin.