The Global Threat of Sinking Deltas

River deltas are essential socio-ecological systems, sustaining dense human populations, major economic centers, and vital ecosystems worldwide. Rising sea levels and subsiding land threaten the sustainability of these valuable landscapes with relative sea-level rise and associated flood, land-loss, and salinization hazards. Despite these risks, vulnerability assessments are impeded by the lack of contemporary, high-resolution delta-wide subsidence observations. Here, we present spatially variable surface elevation changes across 40 global deltas using interferometric synthetic aperture radar. Using this dataset, we quantify delta surface elevation loss and reveal the prevalence and severity of subsidence in river deltas worldwide. Our analysis shows that in 37% of global deltas, groundwater extraction is the primary anthropogenic driver of land subsidence. In other deltas, anthropogenic factors such as reduced sediment supply, urban expansion, and groundwater loss contribute secondarily to additional subsidence and exacerbated elevation loss. Furthermore, we find that contemporary subsidence surpasses absolute (geocentric) sea-level rise as the dominant driver of relative sea-level rise for most deltas in the 21st century. These findings emphasize the need for targeted interventions addressing subsidence as an immediate and localized challenge, in parallel with broader efforts to adapt to climate change-driven global sea-level rise.