More than half of India major river deltas are sinking faster than global sea levels are rising, putting millions of people at growing risk of floods, land loss and displacement, a new global study has found. Published in the journal *Nature*, the research points to excessive groundwater extraction as the single biggest driver accelerating land subsidence across several densely populated delta regions.
The study identifies the Ganga–Brahmaputra, Brahmani, Mahanadi, Godavari, Cauvery and Kabani deltas among those experiencing rapid sinking of land. Researchers warn that in many of these regions, the pace of subsidence now exceeds the rate of sea-level rise, compounding flood risks even without extreme climate events.
River deltas may occupy just about one per cent of the world’s land area, but they support between 350 and 500 million people globally and host some of the world’s largest cities. In India, these low-lying landscapes are critical for agriculture, fisheries, transport and trade, yet their natural resilience is being steadily eroded.
Subsidence Emerges as a Bigger Threat Than the Sea
The global analysis covered 40 major river deltas across 29 countries, home to more than 236 million people who face increasing flood risks in the near future. Using high-resolution satellite data, researchers found that between 2014 and 2023, over half of these deltas experienced land subsidence of more than 3 millimetres per year.
In 13 deltas worldwide, including India’s Brahmani, Mahanadi and Godavari, average subsidence rates exceeded current global mean sea-level rise of about 4 millimetres annually. Nearly 50 per cent of all deltas studied showed widespread sinking across more than 90 per cent of their area, with the Ganga–Brahmaputra delta among the most severely affected.
Brahmani and Mahanadi stood out as two of the fastest-sinking deltas in the world. Around 77 per cent of the Brahmani delta and 69 per cent of the Mahanadi delta are subsiding, with large areas sinking at rates faster than 5 millimetres per year. Overall, the study estimates that between 54 and 65 per cent of the world’s habitable delta land is now sinking.
Major Cities and Millions at Rising Flood Risk
Large deltas account for most of the global land loss. Seven river systems including the Ganga–Brahmaputra, Nile, Mekong and Mississippi together make up nearly 57 per cent of the total subsiding delta area worldwide. In India, land subsidence is occurring faster than regional sea-level rise in several deltas, intensifying flood risks even in normal monsoon years.
Major cities located in delta regions are also sinking at alarming rates. Kolkata, situated in the Ganga–Brahmaputra delta, is among the cities experiencing significant subsidence, alongside Dhaka, Bangkok, Alexandria and Shanghai. This increases vulnerability to flooding, infrastructure damage and long-term displacement of urban populations.
The study highlights that deltas are among the world’s most fragile ecosystems. As low-lying landforms, often less than two metres above sea level, they face multiple overlapping threats, including rising seas, storm surges, saltwater intrusion, changing rainfall patterns and human-driven land subsidence. These pressures damage farmland, disrupt freshwater supplies, accelerate wetland loss and weaken natural flood buffers.
Groundwater Overuse Driving an Environmental Crisis
Researchers identify excessive groundwater extraction as the primary cause of subsidence in the Ganga–Brahmaputra and Cauvery deltas. Intense demand from agriculture, industry and domestic use in densely populated regions has led to groundwater being pumped out faster than it can be naturally replenished. As underground sediments compact, the land surface sinks, often irreversibly.
In deltas such as the Mahanadi and Kabani, subsidence is driven by a combination of groundwater depletion, reduced sediment supply due to upstream dams, and land-use changes linked to population growth. The study notes that river regulation has cut off the seasonal flow of silt that historically helped deltas maintain their elevation, mirroring patterns seen in the Nile, Po and Mississippi deltas.
The authors classify many Indian deltas as “unprepared divers” regions facing high relative sea-level rise but lacking adequate institutional capacity and financial resources to adapt. Indigenous and rural communities are particularly vulnerable, as they often live in the lowest-lying areas and face cultural and economic barriers to relocation.
The study warns that without urgent measures to regulate groundwater extraction, restore sediment flows and strengthen long-term adaptation planning, India sinking deltas could face escalating floods, land loss and forced migration in the decades ahead.