Relevance: GS-1 (Geography – Urbanization, Water Resources) & GS-3 (Science & Tech, Disaster Management) | Source: The Hindu

1. What is the Core Issue?

Recent satellite data from NASA confirms that Mexico City is facing a massive crisis: it is one of the fastest-sinking cities in the world.

• The Data: The city is sinking (subsiding) at an alarming rate of 2 cm per month (nearly 25 cm per year).
• The Damage: Over the last 100 years, the city’s ground level has dropped by a massive 12 meters, severely damaging its infrastructure.

2. Why is the City Sinking?

To explain this simply to students, the disaster is a mix of bad geography and human mistakes:

• Weak Foundation: The city was historically built on top of a soft, muddy, ancient lake bed.
• Human Action (Anthropic Cause): To supply drinking water to 22 million people, the city aggressively pumps out water from deep underground (aquifers).
• The Collapse: When massive amounts of water are pumped out, the underground soil spaces become empty. Unable to support the heavy weight of the city above, the soil simply collapses, causing the ground to sink.
• The Vicious Cycle: As the ground sinks unevenly, it breaks underground water pipes. This creates massive water leaks and shortages. To fix the shortage, the city pumps even more groundwater, which makes the sinking even worse.

3. The Technology: What is NISAR?

The exact data tracking this disaster was collected by the NISAR satellite.

• The Partnership: NISAR stands for NASA-ISRO Synthetic Aperture Radar. It is a historic joint space mission between the United States and India.
• How it Works: It uses advanced radar technology (SAR) that can see through thick clouds and darkness. It scans the Earth every 12 days and can detect ground movements as tiny as a few millimeters.
• The Administrative Benefit: By looking at this satellite data, administrators can “see below the surface.” It allows governments to map vulnerable areas and plan disaster mitigation before buildings and roads collapse.

4. Strategic Significance for India 

This topic bridges a global crisis with our own regional realities:

• Urban Sinking in India: Indian cities built on soft soils (like Kolkata) and fragile Himalayan towns (like Joshimath) face similar sinking risks due to unchecked construction and heavy groundwater pumping.
• Flood & Infrastructure Management: For regions tackling complex hydrology—such as the annual flooding of the mighty Brahmaputra—NISAR is a game-changer. Because its radar can see through heavy monsoon clouds, it will help authorities monitor soil moisture, predict deadly landslides, and ensure the structural safety of vital river bridges and embankments across the Northeast.

UPSC Value Box

• Subsidence: The formal geographical term for the gradual caving in or sinking of an area of land, heavily linked to the depletion of underground water.
• Aquifer: A deep underground layer of water-bearing permeable rock, gravel, or sand from which we extract groundwater using tube wells.
• NISAR: A dual-frequency radar imaging satellite built jointly by NASA and ISRO to map Earth’s surface changes globally.

With reference to the NISAR mission and urban geological challenges, consider the following statements:

1. The NISAR mission is a joint initiative between NASA and the European Space Agency (ESA) to exclusively monitor the melting of polar ice caps.
2. Synthetic Aperture Radar (SAR) technology enables satellites to track Earth’s surface changes with extreme precision, regardless of cloud cover.
3. The rapid urban subsidence observed in Mexico City is primarily attributed to the excessive extraction of groundwater from its underlying aquifers.

Which of the statements given above is/are correct? (a) 1 and 2 only (b) 2 and 3 only (c) 1 and 3 only (d) 1, 2 and 3

Correct Answer: (b)