When a cyclone passes, its effects are often measured at the surface — strong winds, heavy rainfall, flooding and storm surges.
But beneath the ground, the response can be less visible.
A recent study published in Scientific Reports examined how extreme weather events affected groundwater at different depths in the Sundarbans, part of the Ganges-Brahmaputra-Meghna delta in India. Researchers analysed seven atmospheric depressions and four tropical cyclones recorded between May 2017 and May 2020, combining groundwater measurements, hydrogeochemical analysis, stable-isotope testing and numerical modelling.
The study found that these events could alter groundwater levels and chemical conditions at different depths. Under certain conditions, they could also enhance seawater movement into freshwater-bearing zones, with mixing observed in aquifers more than 100 metres below the surface.
The findings highlight an important point: in coastal environments, extreme weather can influence groundwater systems in ways that are not immediately visible from the surface.
The Impact Doesn't Stop at the Surface
Groundwater is not a static resource. Its movement is influenced by rainfall, groundwater flow, hydraulic gradients, pressure conditions and interactions between surface water and underground aquifers.
The Sundarbans study found that groundwater did not respond uniformly at different depths. Shallow aquifers generally showed faster and more pronounced changes, while disturbances in deeper groundwater could persist for longer periods.
This depth-dependent response matters because coastal aquifers contain both freshwater and saline water, and the balance between them can change when groundwater conditions are disturbed.
The study therefore provides a closer look at an often-overlooked connection: Extreme Weather → Groundwater Movement → Changes in Aquifer Conditions
Rather than affecting only surface water, extreme weather can influence the underground water system as well.
When Freshwater Meets Seawater
The Sundarbans is a low-lying delta where groundwater systems are naturally connected to rivers, tidal processes and the surrounding coastal environment.
When hydraulic conditions within an aquifer change, the movement and distribution of freshwater and saline water can also change.
The study indicates that extreme weather events can enhance seawater ingress and contribute to lateral mixing within coastal aquifers, including aquifers more than 100 metres deep.
However, this does not mean that every cyclone will automatically make groundwater saline.
The response depends on factors such as the characteristics of the aquifer, the depth of groundwater, the distance and intensity of the extreme weather event, and the existing hydraulic conditions.
This distinction is important. The research points to a potential mechanism through which extreme weather can affect coastal groundwater quality — not a universal conclusion that all coastal groundwater will become saline after a cyclone.
Why Salinity Matters
When seawater mixes with freshwater, salinity becomes an important water-quality parameter.
For water-treatment applications, TDS (Total Dissolved Solids) is another commonly used indicator of the concentration of dissolved substances in water. Changes in TDS and salinity can influence how water needs to be treated and what operating conditions are appropriate.
For coastal communities and water-treatment operators, this makes continuous water-quality monitoring particularly important.
The question is not simply whether groundwater is “clean” or “polluted.” It is about understanding the actual feed-water conditions — including its TDS, salinity and other characteristics — before selecting an appropriate treatment process.
From Groundwater Changes to Water Treatment
Reverse osmosis (RO) is widely used for treating brackish and saline water. By applying pressure across a semi-permeable membrane, RO can separate dissolved salts and other substances from the feed water.
But RO performance depends on the water entering the system.
Feed-water TDS, salinity, pressure, temperature and fouling potential can all influence membrane performance and system operation. For this reason, understanding the characteristics of the source water is an essential part of selecting and operating an RO system.
In coastal areas where groundwater may be influenced by seawater mixing, treatment solutions need to be matched to the actual water conditions rather than relying on a one-size-fits-all approach.
Built for High-Salt Water
At HJC, high-salinity water is at the center of our RO membrane technology.
From brackish water to high-TDS applications, HJC develops RO membrane solutions for different water-treatment requirements, with a focus on stable desalination performance under demanding feed-water conditions.
The Sundarbans study offers a broader reminder: water quality can be influenced by processes taking place far below the surface, and those changes may vary from one aquifer and depth to another.
Understanding the water comes first. Choosing the right treatment technology comes next.
HJC — Innovator for High Salt Water.