A study published today in Nature shows that many of the world's major river deltas are sinking faster than sea levels are rising, potentially affecting hundreds of millions of people in these regions.
The major causes are groundwater withdrawal, reduced river sediment supply, and urban expansion.
The research provides the first high-resolution, delta-wide assessment of elevation loss across 40 river deltas worldwide. 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.
The findings show that in nearly every river delta examined, at least some portion is sinking faster than the sea is rising. Sinking land, or subsidence, already exceeds local sea-level rise in 18 of the 40 deltas, heightening near-term flood risk for more than 236 million people.
Using advanced satellite radar technology, the team created a map of surface elevation change across river deltas in five continents. Each pixel of the high-resolution map corresponds to 75 square meters of the surface.
Deltas experiencing concerning rates of elevation loss include the Mekong, Nile, Chao Phraya, Ganges–Brahmaputra, Mississippi, and Yellow River systems.
"In many places, groundwater extraction, sediment starvation, and rapid urbanization are causing land to sink much faster than previously recognized," Ohenhen said.
Some regions are sinking at more than twice the current global rate of sea-level rise.
"Our results show that subsidence isn't a distant future problem — it is happening now, at scales that exceed climate-driven sea-level rise in many deltas," said Shirzaei, co-author and director of Virginia Tech's Earth Observation and Innovation Lab.
Groundwater depletion emerged as the strongest overall predictor of delta sinking, though the dominant driver varies regionally.
"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."
This research was supported by the National Science Foundation, the Department of Defense, and NASA.
Original study : DOI: 10.1038/s41586-025-09928-6
