A global analysis of groundwater depletion has concluded that in many of the world’s major agricultural regions demand has outstripped supply for groundwater use. According to the study, published in the journal Nature, almost a quarter of the global population live in a region where groundwater is being abstracted faster than it can be replenished.   

The study was conducted by researchers at McGill University, Montreal and the University of Utrecht in the Netherlands. Using computer modelling and groundwater usage data, the researchers were able to estimate the global supply of groundwater relative to demand. In so doing they revealed that, for the 800 aquifers measured, the current groundwater footprint, or area above ground reliant on water from underground, is larger than the aquifers themselves at 20 per cent of those studied. This means an estimated 1.7 billion people, mostly in Asia, are living in areas where groundwater resources are threatened.

Massive aquifers which humans rely on for drinking water, household use and irrigation also support vital environmental processes, including forests, streams and the wildlife which inhabit them. However, the joint study showed that in some of the world’s most significant agricultural regions, including California’s Central valley, Egypt’s Nile Delta and the Upper Ganges, groundwater recharge rates have fallen below demand.

Hydrogeologists who led the study said their findings have worrying implications for local agriculture and ecosystems, as overstressed water resources will result in long term shortages and have adverse effects on vital ecosystem functions. Experts have hailed the study as the first which accounts for environmental health as well as human demand; there have been calls for research and policy to take a more holistic approach and view human activity and ecosystem functions as interlinked.

Overall, 20 per cent of the 800 aquifers examined worldwide are currently being overexploited, according to the international team of scientists. What is more, some of the most densely populated and agriculturally significant sites are amongst the worst affected; the Upper Ganges’ aquifer has a ‘groundwater footprint’ over 50 times the size of its capacity.

The scientists acknowledge that, as their study focuses on recharge rates, it does not answer the question of how much water is stored underground, and so how long supplies will last at the current rate of extraction. What it does demonstrate is that, throughout a number of global regions, many of which transcend national boundaries, water use is unsustainable.

In fact, the study’s authors posited that a more comprehensive analysis of groundwater stocks would paint an even grimmer picture. It is thought that population growth, climate change and consequent droughts and the expansion of agriculture in sensitive regions will exacerbate the problem.  

The researchers called for moves towards more sustainable water management and a joined up approach from all nations. Tom Gleeson, the study’s lead author, said that around 99 per cent of planet’s fresh, unfrozen water is groundwater and that “It’s this huge reservoir that we have the potential to manage sustainably, if we choose to.”

Gleeson recommended placing limits on water extraction and introducing more sustainable agricultural techniques and efficient irrigation systems to reduce water use in the areas which are “critical to agriculture” and have been shown to be overexploiting water resources. He added that more sustainable diets, including a drastic reduction in consumption of meat and animal products which carry large environmental footprints, would also help to address overuse.

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