Sinking Coastal Cities, Rising Sea Levels: Global Warming Causes Double Trouble

A recent study demonstrates that global warming is creating two distinct problems: sinking coastal cities and rising sea levels.

Parts of many large coastal cities have been sinking faster than the sea is rising, according to research from Nanyang Technological University, the Jet Propulsion Laboratory of NASA, and another researcher from ETH Zürich.

The team describes how they used satellite-based radar to gauge the amount of land subsidence in 48 of the world's largest cities in their paper that was published in the journal Nature Sustainability.

Weight of Buildings + Compaction

According to earlier studies, global warming is melting ice all over the world, which is raising sea levels.

Towns and cities that are close to the sea are very concerned about this rise in sea levels.

A different issue that affects many cities is land subsidence, in which the ground sinks as a result of the removal of gas or groundwater and the compaction of the ground brought on by the enormous weight of buildings erected on top of it.

Rising Sea Levels + Sinking Land

In this new study, the researchers noted that coastal cities may face serious issues in the years to come as a result of rising sea levels combined with sinking land. The researchers accessed and examined radar data from NASA satellites, measuring the altitude of land all over the world to learn more about the severity of the issue.

Over the course of four years, from 2014 to 2020, the researchers measured land subsidence in 48 of the world's largest cities. They discovered that almost all of the cities they looked at had some level of land subsidence. Additionally, in 44 of the cities, some regions were sinking more quickly than the sea was rising.

According to earlier studies, the rate of sea level rise is about 3.7 mm annually. According to their research, some urban areas are experiencing up to 20 mm/year of land subsidence. For instance, Ho Chi Minh City's median rate was 16.2 mm/year. They also looked more closely at some cities, like Rio de Janeiro, and discovered that if action is not taken to slow the sea level rise, by 2030, about 2 sq km of land will be underwater, Phys Org reports.

Subsidence

According to NASA, the term "relative" sea level refers to sea level as measured by land. Subsidence, or sinking land, causes higher sea levels and a greater risk of flooding in coastal areas. I

n contrast, raising land lowers sea levels and encourages coastlines to move toward the sea.

Vertical land motion, or VLM, is the collective term for subsidence and uplift and typically happens at rates of only a few millimeters annually.

Although it might seem insignificant, it can contribute significantly to sea level rise and result in immeasurable harm, as is strikingly evident in Venice, Italy.

We can comprehend VLM and its effects on coastal sea level by using advanced computer models in conjunction with measurements of VLM from the ground and space.

The primary tool historically has been leveling, which involves scientists repeatedly going outside and measuring the difference between two points.

Although this is still a crucial technique, over the past 30 years or so, space-borne instruments have completely changed how we can measure and comprehend VLM.