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A new global study finds several major Indian river deltas are sinking faster than sea levels are rising
The Ganga–Brahmaputra, Mahanadi, Brahmani and Godavari deltas are among those where land subsidence now outpaces sea-level rise
Researchers say excessive groundwater extraction is a key driver, increasing flood risks for millions living in delta regions
Several of India’s major river deltas are sinking at alarming rates due to a combination of excessive groundwater extraction and rising sea levels, according to a new global study.
The research, published in the journal Nature, identified the Ganga-Brahmaputra, Brahmani, Mahanadi, Godavari, Cauvery and Kabani deltas as among those experiencing significant land subsidence, placing millions of people at growing risk of flooding.
The study underlined that human activity was the dominant driver of subsidence in river deltas, with groundwater extraction identified as the major culprit accelerating land sinking in many regions.
The analysis examined 40 major river deltas across 29 countries on five continents. Together, these deltas are home to more than 236 million people who face increasing flood risk in the near future.
River deltas occupy just 1 per cent of the world’s land area, yet support between 350 and 500 million people, or nearly 6 per cent of the global population. They also host 10 of the world’s 34 megacities.
These ecosystems play a crucial role in shaping socioeconomic, ecological, and energy-related functions by supporting agricultural productivity, fisheries, ports, transportation, and maritime trade at domestic, regional, and global levels.
Despite this importance, the study warned that they are among the world’s most fragile ecosystems. As low-lying landforms — with extensive areas less than two metres above sea level — deltas are highly vulnerable to rising seas, storm surges, land subsidence, shifting rainfall and temperature patterns, and other climate-driven pressures.
These combined threats damage farmland, disrupt freshwater supplies, increase saltwater intrusion, accelerate wetland loss, worsen coastal and river flooding, and place infrastructure at risk.
The study notes that these impacts can reinforce one another.
“Land loss and freshwater scarcity may drive displacement and migration, heightening competition for dwindling resources and fuelling social tensions,” the authors said, adding that such intersecting pressures make deltas “the most fragile landscapes on Earth”.
Among the various threats, land subsidence — the gradual sinking of the Earth’s surface — has emerged as a major contributor to risk in river deltas.
The researchers selected deltas based on subsidence rates and horizontal land motion measured at 75-metre resolution, focusing on areas with populations exceeding three million, historically recognised sinking deltas, and less-populated but ecologically and economically important regions.
Their analysis shows that between 2014 and 2023, more than half of the deltas experienced subsidence rates exceeding 3mm per year. In 13 deltas (Nile, Po, Vistula, Ceyhan, Brahmani, Mahanadi, Chao Phraya, Mekong, Red, Ciliwung, Brantas, Godavari and Yellow River) average subsidence rates exceeded current estimates of global mean sea-level rise of about 4 millimetres (mm) per year.
The study found that 35 per cent of the total delta area analysed is sinking, and in 38 of the 40 deltas, more than half of the area showed subsidence. Nearly 50 per cent of the deltas — including India’s Brahmani, Mahanadi and Ganga-Brahmaputra — showed widespread subsidence affecting more than 90 per cent of their area, including Brahmani, Mahanadi and Ganga-Brahmaputra in India.
Brahmani and Mahanadi stood out among the fastest-sinking deltas, with 77 per cent and 69 per cent of their respective areas subsiding, and large portions sinking at rates faster than 5 mm per year.
The researchers calculated that around 460,370 square kilometres of delta land worldwide is exposed to subsidence. When set against an estimated 710,000 to 855,000 square kilometres of habitable delta terrain globally, this means between 54 per cent and 65 per cent of the world’s deltas are now sinking, based on analysis of 40 river deltas.
Seven major deltas — Ganga-Brahmaputra, Nile, Mekong, Yangtze, Amazon, Irrawaddy and Mississippi — account for about 57 per cent of the total subsiding delta area worldwide, covering roughly 265,000 square kilometres.
In 18 of the 40 deltas analysed, including India’s Brahmani, Mahanadi, Ganga-Brahmaputra and Godavari, the study found that local land subsidence is occurring faster than regional geocentric sea-level rise, compounding flood risk even in the absence of extreme sea-level change.
Several major cities located in delta regions are also sinking at rates equal to or higher than their surrounding landscapes. Kolkata, located in the Ganga-Brahmaputra delta, is among the cities experiencing significant subsidence, alongside Alexandria in the Nile delta, Bangkok in the Chao Phraya delta, Dhaka, and Shanghai.
This increases their vulnerability to flooding, infrastructure damage and long-term displacement.
The study identifies excessive groundwater extraction as a primary cause of subsidence in the Ganga-Brahmaputra and Cauvery deltas, largely driven by unsustainable use for agriculture, industry and domestic supply in densely populated regions.
When groundwater is extracted faster than it can be replenished, underground sediments compact under their own weight, leading to irreversible surface-level decline. While natural geological compaction occurs slowly, the authors of the paper noted that human activity has accelerated the process into an urgent environmental crisis.
The Mahanadi and Kabani deltas are affected by a combination of groundwater depletion, reduced sediment supply due to upstream dams and levees, and population-driven land-use changes.
Like many deltas worldwide, Indian deltas are increasingly deprived of the seasonal silt deposits that historically maintained their elevation, as river regulation and infrastructure disrupt natural sediment flows.
The study points out that this pattern mirrors what has already occurred in the Nile, Po and Mississippi deltas, where dams and flood-control systems have caused severe sediment deficits and rapid elevation loss.
The researchers classify many Indian deltas as “unprepared divers” — regions facing high rates of relative sea-level rise but with low adaptation readiness due to institutional and financial constraints.
This lack of preparedness disproportionately affects Indigenous and rural communities, who often live in the lowest-lying areas — below one metre above sea level — and face significant barriers to relocation due to cultural, economic and subsistence ties to the land.
The authors warned that without urgent action to regulate groundwater extraction, restore sediment flows and strengthen adaptation planning, India’s deltas — and those elsewhere — will face escalating risks from flooding, land loss and displacement in the coming decades.