New research involving the University of East Anglia (UEA) has unveiled the alarming rate at which the world’s river deltas are sinking, primarily due to human activities. This groundbreaking study, published in Nature, highlights the urgent need for intervention as these deltas, home to hundreds of millions of people, face increasing risks of flooding.
Led by the University of California, Irvine, and involving researchers from the Tyndall Centre for Climate Change Research at UEA, the study identifies groundwater extraction as the primary driver of delta subsidence. The findings indicate that more than 236 million people living in these regions are at heightened risk of flooding in the near future.
Understanding the Causes of Delta Subsidence
The research team quantified the contributions of various human activities, such as groundwater extraction, sediment starvation, and urbanization, to the sinking of these deltas. This comprehensive analysis allows for a clearer understanding of the dominant causes, enabling communities to prioritize local interventions alongside broader climate adaptation strategies.
“Our study provides the first delta-wide, high-resolution subsidence observations across 40 major river delta systems, revealing not just where land is sinking, but quantifying how much,” said Leonard Ohenhen, UC Irvine assistant professor of Earth System Science and lead author of the study.
Co-author Prof Robert Nicholls, of UEA and the University of Southampton, emphasized the significance of these findings: “The dominance of subsidence over sea-level rise is striking. In every delta that we monitored, at least some portion is sinking faster than the sea surface is rising.”
Global Impact and Regional Variations
The study highlights significant regional variations in subsidence rates. For instance, the Fraser Delta in Canada is sinking at less than one millimeter per year, whereas China’s Yellow Delta experiences subsidence exceeding one centimeter annually. In many densely populated deltas, such as the Mekong, Chao Phraya, and Nile, vast areas are sinking faster than current sea-level rise rates, threatening millions of inhabitants.
In the United States, the Mississippi River Delta has a well-documented history of subsidence. The new analysis confirms this trend, with the delta sinking at an average rate of 3.3 millimeters per year, compared to the regional Gulf Coast sea-level rise of 7.3 millimeters per year. Some areas are subsiding even faster, exacerbating land-loss concerns in coastal Louisiana.
Implications for Climate Change and Flood Risk
While climate-driven sea-level rise remains a significant long-term threat, the study underscores that the immediate danger for delta communities is the ground sinking beneath them. The combined effects of subsidence and rising sea levels increase the risk of flooding and submergence in deltaic regions.
“These results give delta communities a clearer picture of what is driving persistent flood risk and overall vulnerability, and that clarity matters,” said Dr. Ohenhen. “If land is sinking faster than the sea is rising, then investments in groundwater management, sediment restoration, and resilient infrastructure become the most immediate and effective ways to reduce exposure.”
Prof Nicholls added: “Measures to address subsidence are complementary to adapting to rising seas, and dealing with subsidence makes us less vulnerable to rising seas.”
Collaborative Efforts and Future Directions
The study’s key collaborators included Manoochehr Shirzaei of Virginia Tech, Jim Davis and Austin Chadwick of Columbia University, Philip Minderhoud of Wageningen University and Research, and Julius Oelsmann of Tulane University. Their collective efforts have provided critical insights into the global subsidence of river deltas, published in Nature on January 14.
As the world continues to grapple with the impacts of climate change, this research highlights the urgent need for targeted interventions to mitigate the risks associated with delta subsidence. By prioritizing local solutions and integrating them with broader climate adaptation strategies, communities can better safeguard themselves against the dual threats of sinking land and rising seas.
