Cyclones can disrupt groundwater, trigger seawater mixing deep below ground: IIT Kharagpur study
Snehal Sengupta
Kolkata, Oct 6 (UNI) Extreme cyclones like Amphan that lashed the city and the state back in 2020 can alter groundwater levels and chemistry more than 100 metres beneath the ground and trigger seawater mixing in deep coastal aquifers, posing an additional threat to drinking-water security in vulnerable delta regions, a study involving researchers from IIT Kharagpur has found.
The study, published in Scientific Reports, examined the impact of Cyclone Amphan and 10 other extreme weather events on groundwater in the Sundarbans, part of the Ganges-Brahmaputra-Meghna delta. Researchers found that cyclones and atmospheric depressions can rapidly change groundwater levels and hydraulic gradients at different depths, disturbing the balance between freshwater and seawater within coastal aquifer systems.
The findings are significant for the Sundarbans and other densely populated coastal regions where groundwater is a major source of drinking water and is already under pressure from salinisation, arsenic contamination, pollution, groundwater extraction and rising sea levels. The researchers said the results point to the need for continuous monitoring of groundwater at multiple depths and for extreme-weather forecasts to be incorporated into water-resource management. The team analysed seven atmospheric depressions and four tropical cyclones - Titli, Fani, Bulbul and Amphan - recorded between May 2017 and May 2020. It combined groundwater-level measurements from different depths with hydrogeochemical analysis, stable-isotope testing and numerical modelling to assess how aquifers responded before, during and after the events.
The study found marked differences in groundwater response with depth. Shallow aquifers generally experienced larger and faster changes, while disturbances in deeper aquifers could continue for longer periods. The researchers said stable-isotope measurements, including analysis of oxygen-18 (δ¹⁸O), helped identify water movement and mixing that was not always evident from changes in groundwater levels alone. Their analysis indicated that extreme events can facilitate the movement of saline water into freshwater-bearing zones, including aquifers more than 100 metres below the surface.
The extent and nature of seawater mixing varied between aquifer depths, suggesting that coastal groundwater systems cannot be effectively managed as a single, uniform resource. The findings have wider implications for tropical deltas across South and Southeast Asia, where large populations depend on groundwater while facing rising sea levels, increasing groundwater demand and more disruptive climatic events. The researchers said groundwater-management measures should include depth-specific monitoring, careful control of extraction and strategic placement of wells to reduce exposure to seawater intrusion.
Protecting deeper aquifers could become increasingly important as climate-related extremes intensify pressure on coastal freshwater reserves. The research was conducted by Abhijeet Mukherjee and Prakrity Majumder of the Department of Geology and Geophysics at IIT Kharagpur, Aditya Bandopadhyay of its Department of Mechanical Engineering, and Kousik Das of the Department of Environmental Science and Engineering at SRM University, Andhra Pradesh. The paper, titled Groundwater vulnerability to Amphan and other recent cyclones in a tropical mega-delta, has been published in Scientific Reports in 2026.
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