Building on March research revealing sea levels underestimated by nearly a foot in many coastal areas—affecting 80 million people below sea level—a new study maps accelerated land subsidence across 40 major river deltas. Subsidence often exceeds sea level rise tenfold, heightening flood risks for megacities from Shanghai to Jakarta.
Recent findings from Wageningen University researchers Katharina Seeger and Philip Minderhoud, detailed in a prior article, showed current sea levels 9.4 to 10.6 inches (24-27 cm) higher than geoid models due to unaccounted ocean currents, winds, and thermal expansion. This doubles estimates of people living below sea level to 80 million, as confirmed by tidal gauge data from 385 locations. Experts like Matt Palmer of the UK Met Office noted systematic underestimation, especially in the Global South.
Complementing this, Leonard Ohenhen at the University of California, Irvine, used satellite radar to map subsidence in 40 major river deltas. In 18 deltas—including the Nile (Egypt), Mekong (Vietnam), Mahanadi (India), and Yellow River (China)—sinking rates surpass sea level rise, sometimes by tenfold. Robert Nicholls of the University of East Anglia praised the high-resolution data.
Urban threats are acute: Shanghai has subsided over 6 feet, Jakarta up to 13 feet since 1970 (prompting Indonesia's capital relocation), and Semarang experiences subsidence 20-50 times faster than sea rise, with recent floods in October 2025 and February 2026. Primary causes are groundwater extraction and dams impeding sediment flow. Franck Ghomsi of the University of Cape Town and others warn of heightened vulnerability.
Hope exists: Scott Jasechko notes subsidence is locally addressable, as Tokyo demonstrated by stabilizing after 15 feet of mid-century sinking via groundwater pumping bans.