Global subsidence of river deltas reveals widespread sinking and varied risks

A Nature study analysed 40 major river deltas using satellite and other datasets and reports about 42,000 km² of delta area now lies below sea level, with roughly 10.2 million people currently exposed; groundwater loss, reduced sediment supply and urban expansion are identified as key contributors.

A new Nature study combines satellite radar, altimetry, gravimetry and population datasets to examine land subsidence and sea-level change across 40 globally important river deltas. The authors report mapped vertical land motion from 2016–2023 and compared those rates with historical and projected sea-level changes to assess combined exposure. The analysis covers deltas on five continents and reports both local variations and broad patterns in drivers of elevation loss. The study highlights persistent challenges for many deltas despite differences in local adaptive capacity. Key findings: - About 42,000 km² of delta land is currently below mean sea level, with an estimated 10.2 million people in those low-lying areas. - Only two deltas (Fraser and Rioni) fall into the study’s “Safe Havens” category of low relative sea-level rise and high adaptation readiness. - Satellite altimetry and tide-gauge comparisons show regional sea-level trends exceeding the global average for many deltas; about 45% of the 40 deltas experience exacerbated regional sea-level rise. - The analysis attributes much of the residual subsidence (after accounting for long-term geophysical processes) to three main human-related drivers: groundwater storage loss, reductions in fluvial sediment supply, and urban expansion. Summary: The study documents widespread contemporary subsidence across major river deltas and shows that combined land sinking and regional sea-level trends increase exposure for large populations living in these areas. It notes that addressing these vulnerabilities will involve attention to subsidence drivers and governance for long-term land elevation, but specific policy measures and actions are undetermined at this time.