India's Coastline Sinking at Alarming Rates, Satellite Study Reveals
A groundbreaking new study has uncovered that extensive stretches of India's 7,500-kilometer coastline are experiencing significant sinking, with rates in many areas surpassing global sea-level rise. Conducted by researchers from the University of Rhode Island in the United States, this first comprehensive satellite-based assessment of coastal land subsidence along India's shoreline recorded a maximum subsidence rate of 44 millimeters per year in localized hotspots, while other regions showed annual sinking ranging from a few millimeters to over 20 millimeters.
Comprehensive Satellite Analysis of Coastal Movement
Titled 'Vertical Land Motion and Human Exposure Across India's Coastal Regions', the study meticulously analyzed eight years of Sentinel-1 satellite radar data from 2016 to 2024. The research focused on measuring vertical land motion within a 100-kilometer coastal buffer zone along India's entire coastline. The team of authors included Quantao Zhu, Pei-Chin Wu, and Meng (Matt) Wei from the Graduate School of Oceanography at the University of Rhode Island, along with lead data scientist Estelle Chaussard from FM Global's research division in the United States.
Millions of Residents Exposed to Subsidence Risks
The study's findings are particularly concerning given the substantial population living in coastal areas. More than 200 million people reside within 100 kilometers of India's coast. Among the 207.4 million residents in this coastal belt, the research revealed that:
- 27.1 million people (13.1%) live in districts subsiding faster than 2 millimeters per year
- 8.5 million people (4.1%) inhabit areas sinking more than 5 millimeters per year
- 3.4 million people (1.6%) face severe subsidence exceeding 10 millimeters per year
Using nearly 4,900 radar interferograms and over 39 million measurement points, researchers identified major subsidence hotspots in several key cities across India.
City-Specific Subsidence Patterns and Rates
The study documented varying subsidence patterns across different urban centers:
- Ahmedabad: More than half of the metropolitan area is experiencing subsidence, with peak rates reaching up to 44 millimeters per year
- Kolkata: While widespread areas show sinking at less than 5 millimeters per year, localized hotspots reach 13 millimeters annually
- Chennai: Mostly localized subsidence under 5 millimeters per year, with peaks up to 11 millimeters annually
- Kochi and Puducherry: Exhibit widespread sinking exceeding 6 millimeters per year across much of their urban areas, with maximum rates of 21 millimeters and 13 millimeters per year respectively
- Kakinada: Shows rates between 5 and 19 millimeters per year, with localized maxima reaching 30 millimeters annually
Major Delta Systems and Accelerating Sea Level Rise
The five major deltas along India's east coast—the Ganges-Brahmaputra, Mahanadi, Godavari, Krishna, and Cauvery systems—also demonstrate extensive sinking, with rates locally reaching 20 millimeters per year or more in certain areas.
Compounding the problem, tide-gauge data indicates that sea levels near Kochi have risen dramatically faster in recent years. Between 1940 and 2000, sea level rose at approximately 1.45 millimeters per year. This increased to around 2.47 millimeters per year between 2000 and 2016, but surged to more than 17 millimeters per year between 2016 and 2025, pointing to a sharp acceleration in relative sea-level rise that significantly amplifies coastal vulnerability.
Population Concentration and Elevation Vulnerabilities
The study found that subsidence was primarily concentrated near population centers, creating disproportionate risks for urban residents. While only 1.7% of coastal land was sinking faster than 5 millimeters per year, 4.1% of the population was exposed to those accelerated rates. Furthermore, more than half of severely subsiding areas lie at elevations below 25 meters above sea level, increasing flood risks for vulnerable communities.
Primary Causes and Drivers of Coastal Subsidence
On the underlying causes, the study noted that subsidence can result from both natural processes and human activities:
- Natural Factors: Tectonic activity, glacial isostatic adjustment, and sediment compaction
- Human-Induced Factors: Surface water drainage, groundwater extraction, mining activities, and structural loading from buildings and infrastructure
The findings strongly suggest that groundwater extraction is likely the primary driver across much of India's coastline, while in delta regions, the subsidence reflects a combination of sediment compaction and groundwater withdrawal.
Critical Implications for Coastal Risk Assessment
The authors issued a stark warning that conventional coastal risk assessments—which consider only climate-driven sea-level rise—may substantially underestimate future flood exposure and vulnerability. They emphasized that accounting for land subsidence is no longer optional but essential for effective long-term resilience planning along India's coasts. The integration of subsidence data into coastal management strategies represents a crucial step toward protecting millions of residents and valuable coastal ecosystems from escalating threats.
