Coastal Cities Are Sinking Faster Than Sea Levels Are Rising

Researchers from the Technical University of Munich (TUM) and Tulane University have found that land subsidence is significantly intensifying sea level rise for millions of people living in coastal regions.

Land Subsidence Is Accelerating Coastal Sea Level Rise

More than 500 million people live in low-lying coastal areas, placing them at the center of one of the most serious risks associated with climate change.

According to researchers from the German Geodetic Research Institute at TUM (DGFI-TUM) and Tulane University in New Orleans, residents of densely populated coastal regions are experiencing an average relative sea level rise of approximately 6 millimeters per year. The findings were published in Nature Communications.

This rate is nearly three times higher than the coastline-weighted global average of 2.1 millimeters per year, which reflects the average relative sea level increase measured along coastlines worldwide. It is also almost twice the climate-driven absolute sea level rise of about 3.15 millimeters per year.

The primary reason for this difference is land subsidence, the gradual sinking of the ground beneath coastal cities and communities. When sinking land combines with rising oceans, the result is a much faster increase in relative sea levels.

Why Is Coastal Land Sinking?

Identifying the exact cause of land subsidence can be difficult because several natural and human-driven processes may occur simultaneously.

Major causes include excessive groundwater extraction, oil and gas production, the compaction of young sediments in river deltas, and the growing weight of expanding cities. Natural factors such as tectonic activity and the Earth’s crustal response to the loss of ancient ice sheets can also influence land movement.

“To understand sea-level rise along coastlines and respond effectively, we must monitor not only the ocean but also the land itself. In densely populated coastal regions, human activities can intensify land subsidence, often through excessive extraction of groundwater and other resources that previously helped stabilize the subsurface. The weight of cities and long-term geological processes can further accelerate this sinking. As a result, the impacts of climate-driven sea-level rise are significantly amplified,” says Dr. Julius Oelsmann, lead author of the study and researcher at DGFI-TUM.

Major Coastal Cities Are Sinking Rapidly

Thailand, Bangladesh, Nigeria, Egypt, China, and Indonesia are among the countries experiencing the highest rates of relative sea level rise. Their population-weighted coastal averages range from approximately 7 to 10 millimeters per year.

The United States, the Netherlands, and Italy are also recording elevated rates, with population-weighted coastal averages of roughly 4 to 5 millimeters per year.

Several major cities have emerged as land subsidence hotspots. Average sinking rates 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 rates can vary dramatically within the same city. In Jakarta, some areas are sinking by as much as 42 millimeters per year, while other parts of the city are rising at the same time.

Geological Uplift Can Reduce Relative Sea Level Rise

Not all coastal regions are sinking. In parts of Sweden and Finland, geological uplift is causing relative sea levels to decline.

The land in these areas continues to rise because of postglacial rebound, a process that began after the last Ice Age. In some locations, the uplift is occurring faster than the oceans are rising.

Groundwater Management Can Help Slow Land Subsidence

Although some causes of land movement are natural, groundwater extraction is a major factor that governments and communities can address directly.

“Groundwater extraction is a leading cause of land subsidence in many large coastal cities. This means local policies and water-management strategies can make a meaningful difference. Better groundwater management, stricter limits on withdrawals, and targeted aquifer recharge can slow subsidence and, in some cases, largely stop it,” says Florian Seitz, Professor of Geodetic Geodynamics and Director of the German Geodetic Research Institute at TUM (DGFI-TUM).

Tokyo demonstrates how effective regulation can be. The city previously experienced land subsidence of more than 10 centimeters per year, while the hardest-hit areas sank by approximately 24 centimeters annually.

Government regulations and the development of alternative water supplies eventually reduced the rate of sinking substantially.

A similar strategy was implemented in the Harris-Galveston region of Texas, where widespread groundwater extraction had become the leading cause of land subsidence. In 1975, officials established the Harris-Galveston Subsidence District to regulate groundwater use, support alternative water supplies, and encourage water conservation.