River Deltas Around the World Are Sinking Faster Than Sea Level is Rising: Groundwater Withdrawal, Reduced Sediment Supply, and Urban Expansion Are the Causes

    

      A new study published in Nature in January 2026 notes that there are river deltas around the world that are sinking faster than sea level is rising. The study examined 40 deltas and found that in 18 of them, the land elevations were subsiding (dropping) faster than sea level rise, and in nearly every delta studied, there are areas where subsidence is exceeding sea level rise. This is increasing the flooding risks for about 236 million people.

     Advanced satellite radar systems were used to measure changes in surface elevation across deltas on five continents. In particular, the Mekong, Nile, Chao Phraya, Ganges-Brahmaputra, Mississippi, and Yellow River deltas are experiencing rapid elevation loss.

     Three major causes are to blame for the subsidence, and all are caused by humans. These are groundwater withdrawal, reduced sediment supply, and urbanization. The study indicates that groundwater depletion is the chief cause, although the main causes vary by region.

     The study was overseen by Virginia Tech geoscientists Manoochehr Shirzaei and Susanna Werth and led by former Virginia Tech graduate student Leonard Ohenhen, now an assistant professor at the University of California, Irvine.

“When groundwater is over-pumped or sediments fail to reach the coast, the land surface drops,” said Werth, who co-led the groundwater analysis. “These processes are directly linked to human decisions, which means the solutions also lie within our control.”

     The authors created a high-resolution map where each pixel corresponds to 75 square meters of the surface. Some deltas are sinking at a rate double that of sea level rise.

     As the abstract below notes, along with flooding risks and land loss, there are also risks of salination of freshwater. This high-resolution study is an important step toward understanding the issue, its causes, and its possible mitigation. As noted in the quote below from the abstract, relative sea level rise is dominated not by climate change but by subsidence.

“…we find that contemporary subsidence surpasses absolute (geocentric) sea-level rise as the dominant driver of relative sea-level rise for most deltas over the twenty-first century. These findings suggest the need for targeted interventions addressing subsidence as an immediate and localized challenge, in parallel with broader efforts to mitigate and adapt to climate change-driven global sea-level rise.”

 

References:

 

Sinking river deltas put millions at risk of flooding: Some of the world’s biggest megacities are located in river deltas threatened by subsidence due to excessive groundwater extraction and urban expansion, compounding the threat they face from sea-level rise. James Woodford. New Scientist. 14 January 2026. Sinking river deltas put millions at risk of flooding | New Scientist

Major river deltas are sinking faster than sea-level rise: A new study published in Nature finds human-driven land sinking now outpaces sea-level rise in many of the world’s major delta systems, threatening more than 236 million people. Kelly Izlar. Virginia Tech. January 14, 2026. Major river deltas are sinking faster than sea-level rise | Virginia Tech News | Virginia Tech

Major river deltas are sinking faster than sea-level rise. Geology Page. May 2, 2026. Major river deltas are sinking faster than sea-level rise | Geology Page

Global subsidence of river deltas. L. O. Ohenhen, M. Shirzaei, J. L. Davis, A. Tiwari, R. Nicholls, O. Dasho, N. Sadhasivam, K. Seeger, S. Werth, A. J. Chadwick, F. Onyike, J. Lucy, C. Atkins, S. Daramola, A. Ankamah, P. S. J. Minderhoud, J. Oelsmann & G. C. Yemele. Nature. Volume 649, pages 894–901 (2026). Global subsidence of river deltas | Nature