Groundwater exploitation and sinking land

Context: In the plains of northwest India (Punjab, Haryana, Delhi, Faridabad), which are heavily dependent on groundwater withdrawal for agricultural practices, land sinking/subsidence has been a problem for years.

Groundwater situation in India:

It is India’s most used water resource, accounting for a quarter of total global groundwater extraction.
According to the 2021 CAG report, groundwater extraction in India (annual use – ~433 billion cubic metres) has exceeded the recharge rate, threatening 80% of potable water over the next two decades.

What is land subsidence?

Land subsidence is defined as the progressive or abrupt sinking of the earth’s surface caused by the elimination or dislocation of subsurface earth components (like aquifers) triggered by natural/human activity.

How groundwater extraction is linked to sinking land?

When the underlying aquifers – deep water channels that are stores of percolated water, aren’t recharged, they run dry. Hence, the layers of soil and rock above them start to sink and the issue is not specific to north India alone.

How severe is the problem in India?

Data from the Sentinel-1 satellite shows that the NCR region sank 15 mm per year (on average) between 2011-2017.
Urbanisation and unplanned growth were major factors → exacerbated groundwater withdrawal → land sinking.

Impact:

If land sinking is expanded out over a large area, this could imply that th region will become flood-prone.
However, if the pace of sinking varies, it could have an effect on civil facilities such as roads, buildings, and residences.
It may cause fundamentals to deteriorate or cracks to form in buildings.

Detecting the link between groundwater and land subsidence:

The Central Ground Water Board (CGWB) – a subsidiary body of the Jal Shakti Ministry, does not analyse the consequences of ‘over-exploitation’
This link only started to become clear from the data of the GRACE (Gravity Recovery and Climate Experiment) satellites that could measure minute changes in gravity on different parts of the Earth’s surface.

Why is it difficult to detect the link?

Unlike land movement from landslides or earthquakes, it is gradual and barely visible annually.
So, it is harder to correlate with structural damage.

What needs to be done?

There needs to be greater recognition that groundwater exploitation has consequences other than water scarcity.
The government and policymakers should have a detailed understanding of the geophysical properties of the areas undergoing subsidence.
Incentivising rainwater harvesting, ensuring strict implementation of laws against illegal mining of groundwater, evaluating building conditions in hazard zones and provisioning of such subsidence in building designs.

Some initiatives

International National : The United Nations-Water Summit on Groundwater 2022: Organised to raise awareness on groundwater conservation.
“Groundwater: Making the invisible visible” campaign run by UN-Water throughout 2022.
Atal Bhujal Yojana is a groundwater management scheme launched in 2019.
Jal Shakti Abhiyan (2019): Launched in 256 waterstressed districts to improve groundwater conditions in these areas.
Aquifer Mapping and Management Programme