Coastal Cities Are Sinking Faster Than the Ocean is Rising

Topic: Environment

Researchers from Germany and the US found that coastal cities are sinking at a rate of 6 millimeters per year. This is three times faster than the global average sea level rise. The main reason for this difference is land subsidence, which is caused by human activities such as groundwater pumping.

Coastal communities around the world face a growing flood threat from two directions. Ocean levels are increasing, while in many densely populated regions, the ground itself is also sinking. A team of researchers from the Technical University of Munich (TUM) and Tulane University found that this downward movement of land is greatly increasing the amount of sea level rise experienced by millions of coastal residents.

More than half a billion people live in low-lying coastal zones, placing them on the front lines of one of climate change's most serious challenges. A team from the German Geodetic Research Institute at TUM (DGFI-TUM) and Tulane University in New Orleans reports that people living in heavily populated coastal regions experience an average relative sea level rise of about 6 millimeters per year.

The main reason for this difference is land subsidence, which is caused by human activities such as groundwater pumping. The precise cause of subsidence is not always easy to determine because several forces can operate at the same time. Among the most important contributors are heavy groundwater pumping, oil and gas extraction, the compression of relatively young sediments in river deltas, and the weight of expanding urban areas.

Some cities are sinking extremely fast. Thailand, Bangladesh, Nigeria, Egypt, China, and Indonesia are among the countries experiencing the highest relative sea level rise. Their population-weighted coastal averages range from roughly 7 to 10 millimeters per year.

Why It Matters

As India's coastline is vulnerable to climate change, understanding how coastal cities around the world are affected can help us prepare for and respond to similar challenges at home.

Key Facts

• More than half a billion people live in low-lying coastal zones worldwide.
• The average relative sea level rise experienced by coastal populations is about 6 millimeters per year, which is three times faster than the global average sea level rise.
• Land subsidence, caused by human activities such as groundwater pumping, is the main reason for this difference.
• Some cities are sinking extremely fast, with rates ranging from 7 to 10 millimeters per year.

Key Terms

Subsidence

The gradual sinking of the ground beneath a coastal city or community.

Land subsidence

The downward movement of land caused by human activities such as groundwater pumping.

Implications

As India's coastline is vulnerable to climate change, understanding how coastal cities around the world are affected can help us prepare for and respond to similar challenges at home.