Delhi sinking fastest among Indian megacities, Pg3.

Key Highlights:

• Delhi is sinking faster than other Indian megacities, with a maximum subsidence rate of 51.0 mm per year.
• Approximately 1.7 million people in Delhi are exposed to the risks of land subsidence.
• The study identifies 2,264 buildings in Delhi as being at high structural risk due to subsidence.
• Land subsidence in Delhi is primarily driven by the compaction of alluvial deposits from extensive groundwater withdrawals.
• By 2055, an estimated 11,457 buildings in Delhi will face a very high risk of damage due to land subsidence.

Detailed Insights:

• The study, published in Nature, analyzed satellite radar observations from 2015 to 2023 to assess land subsidence in major Indian cities.
• Besides Delhi, the study identifies Mumbai (262.36 km²) and Kolkata (222.91 km²) as having larger areas affected by subsidence. Delhi has 196.27 km² area affected.
• The research links land subsidence to groundwater depletion, changes in monsoon patterns, and the broader impacts of climate change.
• The study highlights localized land uplift in areas near Dwarka, Delhi, at a rate of 15.1 mm per year, indicating varied geological activity within the region.
• The National Capital Region (NCR) shows subsidence hotspots in Bijwasan (28.5 mm/year), Faridabad (38.2 mm/year), and Ghaziabad (20.7 mm/year).
• Changes in monsoon dynamics, including delayed onsets, earlier offsets, and variable precipitation, are straining aquifers and accelerating subsidence.

Key Concepts Involved:

• Land Subsidence: The sinking or settling of the Earth's surface due to various factors.
• Groundwater Depletion: The long-term decline in the quantity of groundwater resources.
• Alluvial Deposits: Sediments like gravel, sand, silt, and clay deposited by flowing water.