New satellite imagery released by NASA in May 2026, derived from the joint NASA-ISRO Synthetic Aperture Radar (NISAR) satellite, has revealed that Mexico City is sinking at a rate of nearly 25 centimeters per year — making it one of the fastest subsiding urban areas in the world. In some localities, the subsidence reaches 2 centimeters per month. The measurements were taken between October 2025 and January 2026 and represent the most precise real-time monitoring of urban land subsidence ever conducted.
This development is significant for UPSC aspirants for several reasons. First, it demonstrates the operational capabilities of the NISAR mission — a landmark collaboration between India and the United States that represents one of the most expensive Earth observation satellites ever built. Second, it illustrates the application of space technology to climate adaptation, disaster risk management, and urban planning — all themes that are increasingly central to international environmental governance. Third, it reflects India’s growing stature as a space power capable of co-developing frontier technologies with the world’s leading space agency.
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The NISAR satellite, launched in January 2024, is a joint mission of ISRO and NASA with a total mission cost of approximately $1.5 billion, making it the most expensive bilateral science collaboration India has ever participated in. Its implications extend far beyond Mexico City: the same technology can monitor fault lines, glacial retreat, agricultural land use, groundwater depletion, and coastal flooding — all of which are directly relevant to India’s vulnerability to climate change.
Background and Context: The NISAR Mission
The NASA-ISRO Synthetic Aperture Radar mission was formally agreed upon in 2014 through a Joint Statement on Civil Space Cooperation between the governments of the United States and India. ISRO contributed the S-band radar and the spacecraft bus, while NASA contributed the L-band radar, the GPS system, solid-state recorder, and payload data subsystem. The satellite operates in a low Earth orbit and completes a full scan of the Earth’s surface every 12 days.
Five Important Key Points
- NISAR uses Synthetic Aperture Radar technology, which can penetrate cloud cover and darkness to collect precise surface measurements, making it superior to optical satellites for continuous monitoring of terrain changes regardless of weather conditions.
- The satellite can detect surface movements as small as 1 centimeter across an area of hundreds of kilometers, enabling it to track subtle geological processes like fault creep, volcanic inflation, and aquifer depletion that are invisible to conventional observation methods.
- Mexico City’s subsidence is driven primarily by the over-extraction of groundwater from the aquifer system beneath the ancient lake bed on which the city was built, causing the clay layers to compact irreversibly — a process that NISAR can now track in near-real-time.
- India’s contribution of the S-band radar to NISAR makes ISRO a scientific partner with data access rights, meaning Indian scientists and institutions can use NISAR data to monitor Indian geographies including the Himalayan glaciers, subsidence in coastal cities like Mumbai and Chennai, and seismically active regions like Uttarakhand and Manipur.
- NASA scientist Paul Rosen has indicated that NISAR data can eventually support building-level subsidence monitoring, which would allow urban planners and infrastructure managers to assess structural risk with unprecedented precision.
The Science of Urban Subsidence: Understanding the Mechanism
Urban land subsidence occurs when the ground beneath cities sinks due to natural compaction, geological processes, or — most commonly and most preventably — the extraction of groundwater from underground aquifers. When water is pumped from aquifers faster than natural recharge can replenish them, the clay and silt layers that hold the water compact under the weight of the overlying material. This compaction is irreversible: once the clay has compressed, refilling the aquifer does not restore the original ground elevation.
Mexico City’s case is extreme because the city was built on the bed of Lake Texcoco, whose soft lacustrine clay is particularly susceptible to compaction. The city has sunk more than 12 meters over the past century, and the process continues. Similar dynamics — though less severe — are observable in many Asian cities including Jakarta (sinking at 1-25 cm per year in different localities), Shanghai, Beijing, and Indian cities including Chennai and the Gangetic plains.
India’s Relevance: Where NISAR Data Will Matter Most
India faces multiple categories of land surface change that NISAR is positioned to monitor with transformative precision. In the Himalayan region, glacial retreat, permafrost thaw, and slope instability due to changing precipitation patterns create landslide and flood risks that claim hundreds of lives annually. NISAR’s 12-day repeat cycle means that dangerous slope movements can be detected before they reach catastrophic thresholds, enabling early evacuation.
In India’s coastal cities, particularly Mumbai, Chennai, Kolkata, and Kochi, a combination of groundwater extraction, sediment compaction, and sea-level rise is creating conditions for accelerating subsidence. Mumbai’s low-lying areas along the Arabian Sea coast and the Thane Creek are particularly vulnerable. NISAR data integrated with India’s National Disaster Management Authority’s early warning systems could substantially improve the country’s preparedness.
The Indo-Gangetic Plain, which is India’s agricultural heartland and the region of most intense groundwater extraction for irrigation, shows measurable subsidence in several districts. This subsidence ultimately compromises the long-term viability of groundwater-dependent agriculture and threatens urban infrastructure in cities including Lucknow, Kanpur, and Patna.
Space Diplomacy: NISAR as a Model for India-US Cooperation
The NISAR mission represents a qualitative advancement in India-US science and technology cooperation. Unlike earlier cooperation that was primarily in the domain of civil nuclear energy and defense technology, NISAR is a purely civilian scientific collaboration with global public good benefits. It reflects the maturation of the bilateral relationship under successive Indian and American governments and demonstrates that India is capable of contributing frontier-level technology to international missions.
The mission also has implications for India’s commercial space sector. The data processing and downlink infrastructure developed for NISAR, combined with India’s expanding network of ground stations, positions ISRO and Indian private space companies to compete in the global Earth observation data market — an industry projected to exceed $11 billion by 2028.
Way Forward
India should establish a National Earth Observation Data Center that integrates NISAR data with data from its own earth observation satellites (RESOURCESAT, CARTOSAT, and the upcoming GISAT series) to create a unified national subsidence and terrain monitoring platform. The National Remote Sensing Centre at Hyderabad should develop specific applications for groundwater monitoring, glacier hazard assessment, and coastal erosion tracking using NISAR data. India should also leverage its NISAR partnership to negotiate data-sharing agreements with the Copernicus program (EU’s Earth observation initiative) to further enhance coverage. Urban local bodies in high-risk cities should be mandated to incorporate satellite-derived subsidence data into building codes and infrastructure planning under the Smart Cities Mission framework.
Relevance for UPSC and SSC Examinations
This topic is relevant for UPSC GS-III (Science and Technology — Space Technology, Applications of Technology in Governance and Disaster Management), GS-I (Geography — Physical Geography, Natural Disasters), and GS-II (International Relations — India-US Relations). For SSC examinations, it covers General Awareness in Science and Technology and Current Affairs. Key terms aspirants must remember include NISAR satellite, Synthetic Aperture Radar, land subsidence, ISRO-NASA collaboration, Earth observation, groundwater depletion, and disaster risk reduction.