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Geography May 03, 2026 5 min read Daily brief · #4 of 25

Mexico City is sinking so quickly, it can be seen from space

The NASA-ISRO joint satellite NISAR (NASA-ISRO Synthetic Aperture Radar) has produced detailed maps showing Mexico City and its surroundings are subsiding by...

GS Paper 1 (Geography) GS Paper 3 (Science & Technology Environment)

What Happened

  • The NASA-ISRO joint satellite NISAR (NASA-ISRO Synthetic Aperture Radar) has produced detailed maps showing Mexico City and its surroundings are subsiding by more than 2 centimetres (approximately 0.8 inches) per month in the most severely affected zones.
  • Measurements were based on data collected between October 25, 2025, and January 17, 2026 — within months of NISAR's launch in July 2025.
  • The primary driver of subsidence is decades of intensive groundwater extraction from the aquifer beneath the city, combined with the compaction of the ancient lakebed sediments under the weight of urban infrastructure.
  • The phenomenon has been observed since 1925; by the 1990s–2000s, some areas were sinking at approximately 35 centimetres (14 inches) annually.
  • NISAR used Interferometric SAR (InSAR) processing of its L-band radar data to generate millimetre-scale precision displacement maps across the metropolitan region.

Static Topic Bridges

NISAR — NASA-ISRO Synthetic Aperture Radar Mission

NISAR is a joint Earth observation satellite developed collaboratively by NASA's Jet Propulsion Laboratory (JPL) and the Indian Space Research Organisation (ISRO). It was launched on July 30, 2025, from the Satish Dhawan Space Centre, Sriharikota, aboard a GSLV rocket, and represents the largest and most technically complex bilateral space collaboration between the United States and India.

  • NISAR carries two SAR instruments: an L-band radar (longer wavelength, ~24 cm) provided by NASA/JPL, and an S-band radar (shorter wavelength, ~12 cm) provided by ISRO — making it the first satellite to carry dual-frequency SAR systems simultaneously.
  • The satellite's antenna is a giant drum-shaped deployable reflector measuring 12 metres (39 feet) in diameter — the largest radar antenna reflector NASA has ever sent to space.
  • NISAR orbits at approximately 747 km altitude and revisits every location on Earth every 12 days, systematically monitoring land surfaces, ice sheets, ecosystems, and hazard zones.
  • Primary science objectives: measuring ground deformation from earthquakes, volcanic activity and glacial melting; monitoring ecosystem biomass changes; and tracking ice dynamics.
  • The L-band radar is particularly suited for penetrating vegetation and soil cover, enabling subsurface movement detection in densely vegetated and urban environments.

Connection to this news: NISAR's L-band InSAR capability allowed it to detect and map centimetre-scale vertical displacement across Mexico City within months of becoming operational — demonstrating its utility for urban hazard monitoring.

Land Subsidence — Causes and Urban Consequences

Land subsidence is the gradual sinking or downward settling of the ground surface, caused by the compaction or displacement of subsurface materials. In urban contexts, the dominant anthropogenic cause is excessive extraction of groundwater from underground aquifers, which reduces pore water pressure and causes fine-grained sediments (especially clay and silt) to compact irreversibly.

  • Mexico City is built on the bed of former Lake Texcoco, which was drained during the colonial period. The lakebed consists of highly compressible lacustrine clays — materials especially prone to irreversible consolidation when dewatered.
  • Differential subsidence (uneven sinking across an area) is particularly damaging to urban infrastructure: it causes building foundations to tilt, pipelines and sewers to fracture, roads to buckle, and drainage systems to reverse gradient.
  • The Angel of Independence monument on Paseo de la Reforma — built in 1910 at ground level — now requires 14 additional steps at its base because the surrounding land has sunk so dramatically while the monument's deep foundations have remained relatively stable.
  • Similar land subsidence problems affect other cities built on alluvial or lacustrine deposits: Jakarta (Indonesia), Tehran (Iran), Ho Chi Minh City (Vietnam), and parts of the Indo-Gangetic Plain.

Connection to this news: Mexico City's subsidence is an extreme case study in the consequences of urban groundwater depletion — with quantified rates now confirmed by satellite-based remote sensing at a scale and precision previously unavailable.

InSAR — Interferometric Synthetic Aperture Radar

Interferometric SAR (InSAR) is a remote sensing technique that compares two or more SAR images of the same area taken at different times. By measuring the phase difference (interference pattern) between the radar signals, InSAR can detect surface displacement as small as a few millimetres over large areas — far exceeding the precision possible with conventional optical imaging.

  • The technique works by generating an "interferogram" — a colour-coded map where each fringe (colour cycle) represents a fixed amount of displacement (typically half the radar wavelength).
  • InSAR is routinely used for: earthquake coseismic deformation mapping, volcanic uplift monitoring, glacier flow measurement, infrastructure subsidence monitoring, and landslide hazard assessment.
  • Limitations include: atmospheric water vapour distortion, decorrelation in densely vegetated areas, and line-of-sight (not vertical) measurement geometry requiring geometric correction.
  • ISRO uses InSAR data from its RISAT series and international satellites (Sentinel-1, ALOS-2) to monitor subsidence in Indian cities and earthquake-affected regions.

Connection to this news: NISAR's dual-frequency InSAR provides unprecedented mapping detail and geographic coverage for subsidence monitoring, enabling urban planners and disaster managers to identify priority intervention zones.

Key Facts & Data

  • NISAR launch date: July 30, 2025
  • Launch site: Satish Dhawan Space Centre, Sriharikota
  • Orbit altitude: ~747 km
  • Revisit period: Every 12 days (complete global coverage)
  • Radar bands: L-band (NASA/JPL) + S-band (ISRO) — world's first dual-frequency SAR satellite
  • Antenna size: 12 metres (39 ft) diameter — NASA's largest ever radar antenna reflector
  • Mexico City measurement period: October 25, 2025 – January 17, 2026
  • Peak subsidence rate recorded: >2 cm per month in worst-affected zones
  • Historical peak: ~35 cm/year in some areas during the 1990s–2000s
  • Root cause: Groundwater extraction from underlying aquifer + compaction of ancient lacustrine (lakebed) clay deposits
  • Duration of documented problem: Since 1925 (over a century)
  • Visible indicator: Angel of Independence monument (built 1910) now requires 14 additional base steps
  • Key technique used: Interferometric SAR (InSAR)
On this page
  1. What Happened
  2. Static Topic Bridges
  3. NISAR — NASA-ISRO Synthetic Aperture Radar Mission
  4. Land Subsidence — Causes and Urban Consequences
  5. InSAR — Interferometric Synthetic Aperture Radar
  6. Key Facts & Data
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