Why Sinking Cities Make Sea-Level Rise Far Worse Worldwide

Imagine streets that edge closer to the sea, not because waves have grown taller alone, but because the ground beneath your feet is quietly collapsing. Cities are heavy. They drink from aquifers. They compress young sediments. Together, these forces turn a global problem—climate-driven sea-level rise—into a local emergency.

Researchers at the German Geodetic Research Institute (DGFI-TUM) and Tulane University have quantified just how big that hidden factor is. In a Nature Communications study they show that densely populated coastal regions see an average relative sea-level rise of roughly 6 millimeters per year. That figure is nearly double the increase produced by climate change alone, and about three times the coastline-weighted global average.

What drives that extra rise? The usual suspects appear again: intensive groundwater pumping, oil and gas extraction, and the slow compaction of deltaic sediments. Add the literal weight of buildings and infrastructure in fast-growing metropolises, plus long-term geological motions such as tectonics and post-glacial adjustment, and you get a patchwork of subsiding and uplifting coasts worldwide.

Cities and countries on the front lines include Thailand, Bangladesh, Nigeria, Egypt, China, and Indonesia, where population-weighted coastal rates hover between 7 and 10 millimeters per year. The United States, the Netherlands, and Italy register elevated rates around 4 to 5 millimeters annually. Within individual cities the contrast can be stark: Jakarta averages 13.7 mm per year, Tianjin about 13.5 mm, Bangkok 8.5 mm. Lagos and Alexandria register 6.7 and 4 mm respectively. In some Jakarta neighborhoods, the ground is falling as fast as 42 millimeters per year, while other districts are stable or even rising.

Not every shore is sinking. In parts of Sweden and Finland the land is still rebounding after the last Ice Age, rising faster than the sea and effectively lowering local flood risk. Context matters. Local geology, human choices, and the pace of climate-driven ocean rise combine to produce wildly different outcomes along neighboring stretches of coast.

There is a practical upside: many subsidence causes are human-made and therefore manageable. Groundwater extraction stands out as a problem that local policies can address. Stricter regulation of withdrawals, managed aquifer recharge, and investment in alternative water sources can slow or halt subsidence in many places.

Policy choices still shape how bad the flood risk gets. Look to Tokyo and the Houston region for proof. Tokyo once faced subsidence exceeding 10 centimeters per year in parts, peaking around 24 centimeters per year in the hardest hit districts; coordinated government action and new water supplies brought those rates down. In Texas, the creation of the Harris-Galveston Subsidence District in 1975 led to regulations and incentives that significantly reduced sinking tied to groundwater pumping.

So what does this mean for coastal planning? Scientists say we must watch both ocean and land. Flood maps that ignore subsidence risk hand planners an incomplete picture. Engineering and adaptation investments—seawalls, drainage upgrades, and retreat plans—work best when informed by measurements of how the ground is moving beneath cities.

The sea is rising. But in many places, the land is helping it—unseen, uneven, and largely preventable. Which cities will act in time?