Chasing aquifers from the sky: Heliborne surveys are mapping India's hidden water reserves

Beneath the sun-baked plains of western India and the densely cultivated stretches of the Indo Gangetic basin, an invisible crisis has been unfolding for decades. As wells run dry and traditional water tables collapse under the weight of modern demand, locating underground water has become a matter of national survival. This account draws on the work of the Central Ground Water Board, where three of the authors, KP Singh, Anirudh Singh and Sashi Kant Singh, are based, alongside Dipankar Saha of the Manav Rachna International Institute of Research and Studies, Faridabad, who formerly served with the Board.

Today, a fleet of helicopters floating over the Indian landscape is offering an extraordinary new perspective. Suspended thirty metres above the earth, hexagonal sensor loops are peering deep into the subterranean bedrock, tracing ancient lost rivers and mapping concealed aquifer architectures with remarkable precision. Without digging a single test pit or sinking a single trial borewell, airborne geophysics is reshaping how India finds, manages and preserves its most vital resource.

A crisis written underground

India's modern economic growth and agricultural productivity are inseparable from its groundwater reserves. The Green Revolution of the 1960s transformed the country's food security, but it also triggered an unprecedented surge in extraction from beneath the surface. Today, India draws roughly 240 cubic km, or 240 billion cubic metres, of groundwater from its aquifers each year, a rate higher than any other nation on Earth. Three out of every five irrigated fields depend entirely on groundwater, as does the vast majority of rural drinking water and more than half of all urban domestic water use.

The limits of traditional drilling

Despite this overwhelming reliance, the techniques used to locate groundwater have remained strikingly primitive for decades. The standard approach involved selecting a surface location, conducting basic local geological or surface geophysical surveys, drilling a deep borewell, and hoping the rock formations below cooperated.

In complex, varied environments, such as the hard rock terrains of central India or the sprawling arid expanses of the west, this trial-and-error method often fails badly. In arid belts, where brackish and saline water zones sit intertwined with small pockets of freshwater, a borewell sunk just a few metres from a productive site can turn up completely dry or yield only useless, salt-heavy water. The need for a rapid, accurate and large-scale diagnostic tool led the Central Ground Water Board, operating under the Union Ministry of Jal Shakti, to look to the skies.

The physics of seeing through rock

The core technology behind this shift is time domain electromagnetics, or TDEM. Rather than relying on manual earthwork or scattered point-by-point ground readings, TDEM trades physical drilling for applied physics. The principle is simple: different subsurface materials, whether saturated river sand, dense dry clay, fractured basalt, fresh water or highly saline groundwater, all conduct electricity at markedly different rates.

To capture these differences, a specialised transmitter coil slung beneath a survey helicopter emits powerful, precisely timed pulses of electromagnetic energy into the ground. These waves penetrate several hundred metres deep. As each pulse switches off, a receiver sensor measures how the secondary electrical signals generated by the underground formations fade over fractions of a second. Scientists decode this decay curve to build high-resolution, three-dimensional digital profiles of what lies beneath.

The gain in efficiency is substantial. Traditional ground-based geophysical crews using vertical electrical soundings might spend an entire field season mapping a few dozen square km. A single helicopter equipped with TDEM sensors, by contrast, can cover thousands of square km in a matter of weeks, flying continuous paths and generating uninterrupted subterranean cross sections that are later validated against real borewell lithology and local pumping data.

Uncovering the lost rivers of the Ganga-Yamuna-doab

The Central Ground Water Board's first major field test of TDEM technology took place over the Ganga-Yamuna Doab near Prayagraj, a fertile agricultural belt increasingly threatened by declining water tables. Between 2016 and 2018, in a joint project with the National Geophysical Research Institute, survey flights covered approximately 1,200 square km to investigate a long-standing hydrological mystery: the existence of ancient, buried river channels, or paleochannels, long believed to belong to historical river systems such as the Saraswati.

The electromagnetic data delivered clear evidence. The survey traced continuous subterranean pathways made of coarse-grained sand deposits buried beneath thick alluvial clay floodplains. Because sand conducts electricity differently to the fine clay around it, the sensor loops mapped these ancient riverbeds in sharp detail. Crucially, these buried paleochannels act as vast, highly porous underground reservoirs holding high-quality freshwater. Encouraged by these results, the Board expanded the survey between 2019 and 2021 to cover roughly 8,500 square km, extending towards Kanpur, redrawing the hydrogeological map across a significant stretch of northern India's agricultural heartland.

Mapping the arid belts at unprecedented scale

Building on this success in the Gangetic plains, the Central Groundwater Board launched one of the world's largest groundwater-focused aerial mapping programmes between 2021 and 2022. The campaign swept across 97,165 square km of arid and semi-arid terrain spanning Rajasthan, Gujarat and Haryana. Helicopters flew more than 40,000 line km across 92 administrative blocks, capturing subsurface data in regions where a single failed well can plunge a rural community into severe water hardship.

Two crises, one technology

India's groundwater crisis takes two very different forms depending on geography, and heliborne data offers targeted insight into both.

In the intensively farmed Indo-Gangetic Plains, decades of subsidised power and water-hungry cropping have driven water levels down rapidly. High-resolution three-dimensional mapping pinpoints exactly where aquifer zones have been depleted, showing water managers where deep storage capacity remains and where artificial recharge can safely be injected.

In the arid west, scarcity takes a different shape, driven by minimal rainfall, erratic monsoons and naturally occurring saline water bodies. Here, heliborne imaging maps the precise boundary between fresh and brackish water, helping farmers avoid unintentionally drilling into salt pockets, and identifies permeable sand channels through which surface runoff can be directed straight into freshwater aquifers without evaporating or degrading along the way.

From data to community stewardship

The real value of these aerial surveys lies in how the data reaches the people who need it. Rather than sitting in static archives, the processed electromagnetic data has been translated into accessible reports at the block and Gram Panchayat level. Local authorities, state agencies and district planners can scan a simple QR code to access detailed maps showing the best locations for check dams, recharge shafts, injection wells and productive borewells.

By pairing airborne geophysics with satellite remote sensing and local ground monitoring, India is moving away from a historically reactive pattern of drilling ever deeper into a depleting resource. In its place, the country is building a comprehensive subterranean atlas that supports proactive, data-driven stewardship, treating groundwater less like an endless reserve and more like a finite account that must be carefully managed. In doing so, this airborne technology is helping ensure that India can protect and replenish the unseen water resources that millions of its people depend on every day.