Hydroclimate change affects tropical lake ecosystems on floodplains in the Pantanal

Global climate change, particularly altered precipitation patterns, has significantly impacted tropical ecosystems like floodplain lakes that are highly sensitive to fluctuations in riverine discharge. Here, we investigate the effects of interannual hydrological changes in the Upper Paraguay River on floodplain lake ecosystems in the Pantanal, the largest tropical wetland on Earth. Our analysis includes a time series of river levels (1985–2023), Landsat imagery, and lake sediment geochemistry datasets that untangle connections among river hydrology, lake basin morphology, and the proliferation of aquatic vegetation. Our results found that Lakes Cáceres, Vermelha, Uberaba, and Negra have significant temporal variations in open water habitats. They are particularly vulnerable to hydroclimatic changes because of their flat lake beds and shallow bathymetry, which promote rapid replacement of open water habitats with dense aquatic macrophyte cover during droughts. Lakes Gaíva and Mandioré are more resistant to changes in the Upper Paraguay River level, with a dominance of open water habitats even during severe drought events. Our time series analysis shows the severe drought of 2019–2020 as a tipping point in the Pantanal’s floodplain lake ecosystems, with the analyzed lakes experiencing marked reductions in open water habitat and expansion of aquatic vegetation. Predictive climate models indicate that more frequent, extended drought may result in floodplain lake ecosystem transformations in the coming decades. Low river levels drive transitions in tropical floodplain lakes, leading to macrophyte and terrestrial vegetation expansion and increased fuel accumulation. These changes elevate wildfire risk, reduce aquatic biodiversity, and threaten local livelihoods that depend on fisheries and other ecosystem services.