Daily Hot Topic

Topic : Sinking Cities in China: A Growing Threat

GS-1 Mains : Geography

Revision Notes

A recent study reveals a concerning trend:

• Over 270 million urban residents in China (more than a third) live in cities experiencing subsidence (sinking land).
• This phenomenon, coupled with rising sea levels, could significantly impact coastal areas.

Key findings:

• The study analyzed 82 cities, finding 37 experiencing subsidence.
• Nearly 70 million people face rapid subsidence exceeding 10mm annually.

What is subsidence?

• Land subsidence occurs when underground materials shift, causing the ground to sink.
• This phenomenon can affect large areas or even localized spots.

Global examples:

• Several megacities worldwide face subsidence, including Jakarta, Manila, New Orleans, Vancouver, and Mexico City.

Recent case in India:

• Land subsidence impacted around 65% of houses in Joshimath, Uttarakhand, in 2023.

Potential future impact (China):

• The study projects a tripling of China’s urban area below sea level by 2120, affecting 55-128 million residents.

This situation highlights the need for:

• Effective land management strategies to address subsidence.
• Climate change mitigation efforts to curb sea-level rise.

Causes of Sinking Cities:

• Groundwater Extraction: Overpumping groundwater compacts the soil, causing the land to subside. This is especially risky in areas with young sediments like river deltas.
• Land Reclamation: Filling coastal areas for development adds weight, compressing the underlying soil and leading to subsidence.
• Mining Activities: Underground mines collapse over time, leaving voids that cause the ground above to sink unevenly.
• Natural Factors: Natural processes like soil compaction, sediment consolidation, and tectonic movements contribute to subsidence.

Impacts of Sinking Cities:

• Uneven Subsidence: Damages infrastructure, buildings (uneven settling), and overall urban stability.
• Traffic and Infrastructure: Disrupts transportation networks like subways and highways, increasing maintenance costs and safety hazards.
• Coastal Vulnerability: Worsens the effects of sea-level rise, making coastal cities more susceptible to flooding. (e.g., Hurricane Katrina in New Orleans)
• Social Disruption: Displacement, loss of livelihoods, and increased vulnerability to disasters can lead to social unrest.

Solutions to Address Sinking Cities:

• Improved Urban Planning: Assess subsidence risks to inform land use decisions and identify vulnerable areas.
• Coastal Protection Measures: Invest in dikes, seawalls, and levees to mitigate subsidence and rising sea levels in coastal areas.
• Deep Soil Mixing: Inject stabilizing agents into the ground to reinforce soil and prevent subsidence.
• Alternative Construction Techniques: Use lightweight building materials and foundation systems to reduce building weight and minimize subsidence risk.

The Way Forward:

• Artificial Recharge: Replenish depleted aquifers by injecting water, reducing the need for excessive pumping and preventing further subsidence.
• Satellite Monitoring: Regularly track subsidence trends using satellite measurements to guide solutions.

Source : https://www.thehindu.com/sci-tech/science/more-than-a-third-of-urban-chinese-living-in-sinking-cities-study-finds/article68174263.ece#:~:text=A%20recent%20study%20by%20researchers,people%20%E2%80%93%20live%2