The Ganga-Brahmaputra delta isn’t just huge; it’s one of the most densely populated deltaic systems, and it’s sinking even faster than the sea is rising. The Ganga Delta’s rapid sinking is turning into a serious climate, social, and environmental mess, and a recent study using data from ESA’s Sentinel-1 radar (2014-2023) found that over 90% of the delta is sinking, and some spots are dropping faster than sea levels are rising.

Right now, the global sea level is rising by about 4 mm each year, mostly because of melting ice and warmer oceans. But in the Ganga Delta, parts are sinking more than 3 mm a year, and in some places, it’s much worse.

Understanding the Sinking: Sea Level Rise vs. Land Subsidence

Deltas, such as the Ganga Delta that stretches over India and Bangladesh, maintain a balance of water levels by depositing sediment.

However, today, two factors are working together:

• Rise in sea levels because of global warming and melting ice.
• Land subsidence due to human and natural compaction.

These two factors are working together to create relative sea-level rise, or the rise in water levels as it is experienced on the surface, which is much higher than the rise in sea levels.

Here are the key data points for Ganga Delta’s rapid sinking:

Also Read: Scientists Warn Global Sea Level Rise May Be Greater Than Previously Calculated

Why the Ganga Delta Is Sinking: The Causes

1. Groundwater Extraction

One of the main causes of land subsidence is the over-extraction of groundwater. Agricultural, industrial, and other uses of groundwater in the delta region lead to a rapid depletion of groundwater, resulting in the compaction of soil and the sinking of the land surface, or essentially the collapse of the land surface.

2. Reduced Sediment Supply

The construction of dams and embankments in the upper regions of the delta has resulted in the trapping of sediment that would otherwise be deposited in the delta region.

3. Urban Growth & Development

In Kolkata and the other cities on the Ganga Delta, urban development (increasing construction) and resource usage (water extraction) create subsidence pressures, or more rapidly sinking rates of the land.

4. Natural or Geologic Processes

While the majority of subsidence that is occurring is due to the natural compaction of delta sediments by gravity over many years, human activity has greatly amplified this process.

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The Dual Threat: Subsiding Land with Rising Sea Levels

When considering relative sea-level rise in the Ganga Delta, it is critical to note that it is not just created by the ocean rising, but also by the sinking of the land, which is causing sea-levels to rise substantially above the land surface as sea-levels rise, as impacted by climate change via subsidence and sea-level rise.

Thus:

• Flooding will occur more frequently, even in the absence of a storm.
• Storm surges will impact the coastline farther inland.
• Saltwater will move into the freshwater supply system and agricultural land, affecting the availability of these resources.
• Urban infrastructure will incur greater damage due to increased demand for services.

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Impact on People, Cities, and Ecosystems

The Ganga-Brahmaputra delta is home to millions who rely on farming, fishing, and coastal jobs. The Ganga Delta’s rapid sinking means the risks get worse for coastal towns and villages, roads and rail lines, drainage systems, mangrove forests like the Sundarbans, clean groundwater, and anyone whose job depends on good farmland.

Even the milder predictions say that by 2100, parts of the delta could see the water rise by as much as 140 cm, way more than if we ignored the land sinking.

Also Read: 30% Ocean Protection Goal Moves Forward As UN Biodiversity Treaty Takes Effect

A Delta at a Crossroads

The Ganga Delta’s rapid sinking is an urgent socio-ecological issue with direct impact on many people and places who are facing this challenge to their way of life. In addition, the compounding effect of land subsidence (which is distinct from sea-level rise) will continue to increase risk, even under moderate warming scenarios. Globally, it has been shown that coastal communities with combined land subsidence and sea-level rise experience a more rapid increase in risk than coastal communities that are not adapted to it.

The window of opportunity for taking meaningful action through local groundwater regulation or international climate mitigation is closing quickly. Urgent, coordinated action is needed to address both the increasing risk to natural systems and human communities in the Ganga Delta, to prevent worsening of these systems and communities in the years to come.

Also Read: Rapid Rise In Coastal Ocean Acidity Surprises Scientists Amid Climbing CO₂ Levels

FAQs

1. What is land subsidence?

Land subsidence refers to the Earth’s surface moving downwards due to natural processes, such as settlement, or due to human activities such as the extraction of excessive amounts of groundwater.

2. How fast is the Ganga Delta sinking?

Satellite analysis of the Ganga Delta shows the average land subsidence rate exceeds 3 mm/year (some places even faster, such as those areas experiencing similar rates of sea-level rise)

3. How does subsidence worsen flooding?

When the land is subsiding towards an increasing sea level, the floodwater travels further inland, increasing the frequency and severity of floods, even without extreme weather, resulting in more significant storm surge and saltwater intrusion.

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