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Scientific Frontline: Extended "At a Glance" Summary: Relative Sea-Level Rise and Land Subsidence
The Core Concept: Coastal regions face severe, accelerated risks from relative sea-level rise, a phenomenon driven by the dual impact of climate-driven ocean expansion and localized land sinking (subsidence).
Key Distinction/Mechanism: While absolute sea-level rise is a global metric caused by warming oceans and melting ice, relative sea-level rise accounts for land subsidence driven by excessive groundwater extraction, urban structural weight, and sediment compaction. Consequently, the effective sea-level rise in densely populated coastal areas is roughly three times higher than the global coastline average.
Major Frameworks/Components:
- Absolute Sea-Level Rise: The climate-driven global ocean increase, measuring approximately 3.15 millimeters per year.
- Population-Weighted Relative Rise: The effective sea-level change experienced by people, averaging 6 millimeters per year in densely populated coastal zones.
- Drivers of Subsidence: Anthropogenic factors (intensive groundwater and resource extraction), the immense structural loads of megacities, sediment compaction in deltas, and natural tectonic shifts.
- Subsidence Hotspots: Major coastal cities experiencing extreme land sinking, such as Jakarta (up to 42 mm/year in some districts), Tianjin, Bangkok, and Lagos.
Branch of Science: Geodesy, Geodynamics, Climate Science, and Hydrology.
Future Application: The development of sustainable urban water management policies, targeted aquifer recharge protocols, and strict regulations on groundwater withdrawal to actively slow or halt rapid coastal land subsidence.
Why It Matters: With more than half a billion people residing in low-lying coastal zones, localized land subsidence drastically multiplies the vulnerability to flooding and infrastructural collapse, making groundwater management an essential climate mitigation strategy.
Densely populated coastal regions in many parts of the world are particularly vulnerable to flooding. The sinking of landmasses exacerbates the impacts of rising sea levels in these areas, as researchers from the Technical University of Munich (TUM) and Tulane University have demonstrated.
Global sea-level rise is one of the greatest challenges of climate change; more than half a billion people live in low-lying coastal zones. A research team from the German Geodetic Research Institute at TUM (DGFI-TUM) and Tulane University in New Orleans has shown that people in densely populated coastal regions experience a relative sea-level rise of about 6 millimeters per year on average. This rate is roughly three times the coastline-weighted global mean of 2.1 millimeters per year, which describes the average relative rise measured worldwide along coastlines. Even when compared with the climate-driven absolute sea-level rise of around 3.15 millimeters per year, the value is nearly twice as high. This amplified rise is caused by sinking land, a process known as subsidence.
Key Drivers of Land Subsidence: Groundwater Extraction, Resource Use, Ice Loss, and Tectonics
According to the researchers, the exact causes of subsidence cannot always be clearly identified. However, the most important and consequential factors include intensive groundwater extraction, oil and gas production, the compaction of young sediments in delta regions, and structural loads in rapidly growing cities. In addition, long-term geological processes, such as tectonics and postglacial adjustments, 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, a researcher at DGFI-TUM.
Subsidence of Up to 42 Millimeters per Year
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 hotspots include Jakarta (−13.7 millimeters per year), Tianjin (−13.5 millimeters per year), Bangkok (−8.5 millimeters per year), Lagos (−6.7 millimeters per year), and Alexandria (−4 millimeters per 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 postglacial rebound following the last ice age—and it does so 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).
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.
Published in journal: Nature Communications
Title: Subsidence more than doubles sea-level rise today along densely populated coasts
Authors: Julius Oelsmann, Robert J. Nicholls, Daniel Lincke, Marta Marcos, Manoochehr Shirzaei, Laura Sánchez, Leonard Ohenhen, Denise Dettmering, Jochen Hinkel, Benjamin P. Horton & Florian Seitz
Source/Credit: Technische Universität München
Reference Number: es051826_01