Scientists Uncover the Hidden Force Making Sea-Level Rise Far Worse Than Expected

Sea-level rise is not just about the oceans. New research shows that sinking land is dramatically increasing flood risk in many coastal cities.

As climate change pushes oceans higher, many of the world’s biggest coastal cities are confronting a second, less visible threat beneath their streets. In places where millions of people live, the ground itself is sinking, increasing flood risk and causing local sea levels to rise faster than global averages.

Now, researchers from the German Geodetic Research Institute at the Technical University of Munich (DGFI-TUM) and Tulane University have quantified just how much this hidden process is amplifying the problem.

Writing in Nature Communications, they report that densely populated coastal regions experience an average relative sea-level rise of about 6 millimeters per year—nearly twice the rate of climate-driven sea-level rise alone and roughly three times the coastline-weighted global average. Their findings suggest that human-driven land subsidence has become a major contributor to coastal flood risk, but one that can often be slowed through local policies.

Key drivers of land subsidence: groundwater extraction, resource use, ice loss, and tectonics

The exact causes of subsidence are not always easy to identify in every location, according to the researchers. Still, several major factors stand out, including heavy groundwater extraction, oil and gas production, the compaction of young sediments in deltas, and the load from buildings and infrastructure in fast-growing cities. Longer-term geological processes, including tectonic movement and post-glacial adjustment, can also contribute.

“If we want to understand sea-level rise along coastlines and respond effectively, we must not only observe the ocean but also the land itself. Especially in densely populated coastal regions, human activities cause the land to subside more strongly – often due to excessive extraction of water and resources that previously stabilized the subsurface. The sheer weight of cities, along with long-term geological processes, can further intensify this subsidence. In doing so, we significantly amplify the effects of climate-driven sea-level rise,” says Dr. Julius Oelsmann, lead author of the study and researcher at DGFI-TUM.

Subsidence of Up to 42 Millimeters per Year

The countries with the highest relative sea level rise include Thailand, Bangladesh, Nigeria, Egypt, China, and Indonesia. In those places, the population-weighted coastal averages were about 7 to 10 millimeters per year. The United States, the Netherlands, and Italy also showed elevated rates, at about 4 to 5 millimeters per year.

Major subsidence hot spots include Jakarta at 13.7 millimeters per year, Tianjin at 13.5 millimeters per year, Bangkok at 8.5 millimeters per year, Lagos at 6.7 millimeters per year, and Alexandria at 4 millimeters per year. Subsidence can differ sharply within the same city. In Jakarta, some areas are sinking by as much as 42 millimeters per year, while other parts are rising.

In some regions, the opposite is happening. Geological uplift is causing the relative sea level to fall along parts of the coast, including in Sweden and Finland. There, the land is still rising after the last Ice Age because of post-glacial rebound, and it is rising faster than sea levels are increasing.

Groundwater Management as a Countermeasure

“In many large coastal cities, groundwater extraction is a major driver of land subsidence. This means that local political and water-management decisions can make a significant difference. Improved groundwater management, stricter regulation of withdrawals, or targeted recharge of aquifers can at least slow subsidence rates and, in some cases, largely halt them,” says Florian Seitz, Professor of Geodetic Geodynamics and Director of the German Geodetic Research Institute at TUM (DGFI-TUM).

Tokyo and the Houston metropolitan region in Texas show that subsidence can be reduced. In Tokyo, subsidence once exceeded 10 centimeters per year and reached about 24 centimeters per year in the hardest hit areas. Government action and alternative water supplies greatly reduced those rates.

In the Harris-Galveston region of Texas, heavy groundwater pumping was also the main cause of sinking land. To address the problem, the Harris-Galveston Subsidence District was created in 1975 to regulate groundwater withdrawals, encourage alternative water sources, and support water conservation.

Reference: “Subsidence more than doubles sea-level rise today along densely populated coasts” by Julius Oelsmann, Robert J. Nicholls, Daniel Lincke, Marta Marcos, Manoochehr Shirzaei, Laura Sánchez, Leonard Ohenhen, Denise Dettmering, Jochen Hinkel, Benjamin P. Horton and Florian Seitz, 16 May 2026, Nature Communications.
DOI: 10.1038/s41467-026-72293-z

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