Satellite data show millions living in rapidly sinking coastal regions

March 6, 2026

In India, five major east coast deltas and many cities along the coastline are sinking more extensively than previously recognized. This widespread land subsidence threatens millions of people living in low-lying coastal regions that already face growing flood risks from sea level rise. 

In a new paper, scientists from the University of Rhode Island Graduate School of Oceanography found that 8.5 million residents live in coastal areas experiencing subsidence greater than 5 millimeters per year. In the five major deltas along India’s east coast, subsidence rates reach up to 20 millimeters per year.

The study, led by GSO doctoral student Quantao Zhu, GSO alum Pei-Chin Wu, Ph.D. ‘24, Professor Meng (Matt) Wei, and FM’s Estelle Chaussard, adds to a growing body of research showing that waterfront cities are facing not just rising seas, but also sinking land.

Global sea levels are rising due to climate change, increasing flood risks for coastal communities worldwide. While subsidence has been documented in many coastal cities across Asia, no previous study has examined land subsidence across India’s coastline at a national scale.

More than 200 million people live within 100 kilometers of India’s coastline, making the region particularly vulnerable to the combined effects of sea level rise and sinking land. To better understand these risks, the researchers created a unified geodetic assessment of vertical land motion across India’s coastal zone, producing high-resolution models of how the land surface is sinking. Using eight years of Sentinel-1 Interferometric Synthetic Aperture Radar (InSAR) time-series data (2016–2024), the team measured subsidence patterns in areas within 100 kilometers of the coastline. Notable hotspots include Ahmedabad, Chennai, Amaravathi, Kochi, Kakinada, and Kolkata.

The findings suggest that coastal subsidence in India is more extensive than previously recognized, posing a significant challenge for long-term land-use planning in coastal zones.

“One of the most surprising findings was how many mid-sized cities are experiencing significant subsidence,” Wei said. “Past research has focused primarily on megacities. We were also struck by how much cropland is subsiding, which could have serious implications for food security for millions of people.”

The researchers believe the primary driver of subsidence across much of India is groundwater extraction. When large volumes of groundwater are withdrawn from fine-grained sediments, the soil compacts because the water that once helped support the ground is removed. This compaction can cause the land surface to gradually sink. India is currently the largest consumer of groundwater in the world, and widespread groundwater depletion has been linked to subsidence in many regions.

Wei and Wu have previously documented similar patterns in other coastal cities. In a 2023 study with GSO Interim Dean Steven D’Hondt, they found that New York City is sinking at a rate of 1 to 4 millimeters per year.

As coastal cities continue to grow, particularly in rapidly developing countries like India, the compounding impacts of sea level rise and land subsidence are becoming increasingly important. The researchers emphasize that subsidence should be incorporated into coastal risk assessments and planning frameworks alongside sea level rise projections.

This project was funded by FM, a company headquartered in Johnston, Rhode Island.