Delhi is sinking faster than any other Indian megacity, recording the highest maximum rate of land subsidence and the largest number of buildings at high structural risk, a new study published in Nature, a multidisciplinary science journal, has revealed. Around 1.7 million people in the Capital, the researchers estimate, are exposed to land subsidence.
The Capital currently has 2,264 buildings categorised as being at high risk from the ongoing land subsidence, according to the study titled “Building Damage Risk in Sinking Indian Megacities”. The findings, published in the journal on October 28, highlight that the city has exhibited a maximum subsidence rate of 51.0 mm per year.
Among the five megacities analysed, Delhi has the third largest area affected by subsidence, at 196.27 km², following Mumbai (262.36 km²) and Kolkata (222.91 km²).
The study has linked land subsidence with groundwater depletion, monsoon variability, and climate change. “In Delhi, the primary driver of land subsidence is the compaction of alluvial deposits caused by extensive groundwater withdrawals,” it reads.
The study notes that “climate change and human actions can accelerate subsidence rates in places lacking adequate adaptation and mitigation strategies.”
It reads, “Surface water supply and groundwater demand in India critically depend on monsoon precipitation for replenishment. However, observed shifts in the monsoon dynamics, characterised by a delayed onset and earlier offset, coupled with variable precipitation intensities, have exerted considerable stress on aquifers in recent decades.”
The paper, authored by researchers from the Department of Earth System Science, University of California; Department of Geosciences, Virginia Tech; and the United Nations University in Richmond Hill, Ontario, analysed satellite radar observations (InSAR) over the period between 2015 and 2023.
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In the National Capital Region (NCR), it identified subsidence hotspots with land subsidence “rates of up to 28.5 mm per year, 38.2 mm per year and 20.7 mm per year in affected areas of Bijwasan, Faridabad and Ghaziabad”. It also observed “localised uplift in some cities, such as areas near Dwarka, Delhi that are rising at a rate of 15.1 mm per year.”
On future risk projections, the authors write, “Our analysis suggests that in 30 years, an estimated 3,169, 958 and 255 buildings in Delhi, Chennai and Mumbai will face a very high risk of damage. Furthermore, in 50 years, 11,457, 3,477, 112, 8,284 and 199 buildings in Delhi, Mumbai, Bengaluru, Chennai and Kolkata are expected to be at very high risk of damage.”
The researchers cautioned that “differential land subsidence may affect future structural damage,” and stressed the need for “a comprehensive building damage record that is spatially explicit, temporally resolved and standardized and that includes both damage attributes and building metadata, along with georeferenced information to align with InSAR-based subsidence measurements.”
They noted that “not all building cracks indicate settlement. Conversely, the absence of visible cracks does not definitively rule out the occurrence of settlement. Navigating this complexity makes it challenging to identify structurally damaged buildings based on conventional techniques and instruments on a large scale, presenting a formidable obstacle for asset managers and policymakers to take preventive actions.”
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The study underlines, “Weather extremes directly influence infrastructure vulnerabilities, and as they become more frequent and intense in the face of climate change, their toll is increasing, too. Thus, the compounding effect of land subsidence, climate change and weather extremes forms a complex and critical nexus that can exacerbate the risk of structural damage.”
