Land Subsidence Causes Dramatic Sea Level Rise

According to the researchers, the exact causes of subsidence cannot always be clearly identified in every case. However, among the most important and consequential factors are intensive groundwater extraction, oil and gas production, the compaction of young sediments in delta regions, as well as structural loads in rapidly growing cities. In addition, long-term geological processes such as tectonics and post-glacial adjustments also play a role.

"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.

Countries with the highest relative sea-level rise include Thailand, Bangladesh, Nigeria, Egypt, China, and Indonesia, where population-weighted coastal averages of around 7 to 10 millimeters per year were calculated. The United States, the Netherlands, and Italy also show elevated values of about 4 to 5 millimeters per year.

Prominent subsidence hot spots include Jakarta (-13.7 mm/year), Tianjin (-13.5 mm/year), Bangkok (-8.5 mm/year), Lagos (-6.7 mm/year), and Alexandria (-4 mm/year). The extent of subsidence can vary greatly within individual cities: In Jakarta, some areas reach rates of up to -42 millimeters per year, while other parts of the city simultaneously show uplift.

Conversely, in some regions geological uplift leads to a relative decrease in sea level along coastlines, as seen in Sweden and Finland. There, the land continues to rise as a result of post-glacial rebound following the last Ice Age - and does so faster than sea levels are increasing.

"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).

Successful examples include Tokyo and the metropolitan region of Houston, Texas. In Tokyo, subsidence rates once exceeded 10 centimeters per year, reaching peaks of around 24 centimeters per year in particularly affected areas. Through government intervention and the introduction of alternative water supplies, these rates were significantly reduced.

Similarly, in the Harris-Galveston region in Texas, intensive groundwater extraction was the main driver of subsidence. In response, the Harris-Galveston Subsidence District was established in 1975 to regulate groundwater withdrawal, promote alternative water sources, and support water conservation measures.