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Water footprint

Posted 14/08/2012 by sevans

Recently in this weekly blog, I highlighted that the Earth is in fact a ‘dry’ planet – and the evidence indicates that it is getting drier; or rather, water is rapidly becoming a scarce resource.  In another earlier blog, I reported that Dutch researchers at Utrecht University had suggested that like ‘peak oil’ there is also a point of ‘peak water’, the maximum amount of water that will be available for use by the global population. And the researchers also expressed concern that we may have passed that water peak and are now depleting underground water reserves that have existed for millennia and have no possibility of being sustained.

Now Utrecht researchers, together with Canadian colleagues from McGill University in Montreal, have combined global groundwater usage data with computer models of underground water resources to produce a measure of water usage compared with supply (Nature, doi: 10.1038/nature11295). This ‘groundwater footprint’ is formally defined in the study as the area required to sustain groundwater use and groundwater-dependent ecosystem services. It is claimed to be the first tool suitable for consistently evaluating the use, renewal and ecosystem requirements of groundwater at an aquifer scale.

And the results are not encouraging, being described by the leader of the study, Tom Gleeson, from McGill University, as ‘sobering’. The footprint shows that we are over-exploiting groundwater in many larger aquifers that are critical to agriculture, especially in Asia and North America.

‘We estimate the size of the global groundwater footprint is currently about 3.5 times the actual area of aquifers and that about 1.7bn people live in areas where groundwater resources and/or ground water-dependent ecosystems are under threat,’ says Gleeson. That said, he also emphasises that 80% of aquifers have a groundwater footprint that is less than their area. This means that the net global value is driven by a few heavily over-exploited aquifers.

Earlier this year, Mona Arnold, the head of the Green Solutions for Water & Waste at Finland’s VTT Technical Research Centre, pointed out that water consumption has risen threefold over the last 50 years, twice as fast as population growth. And because groundwater is being used to support this growth, the quality for use as drinking water is deteriorating and reserves are falling. She highlighted that in large cities such as Mexico City, Bangkok, Beijing, Shanghai and Manila, the depths for access to groundwater have increased from 10m to 50m. 

But Arnold also pointed out that domestic water consumption accounts for around just 8% of total global water consumption, depending on the country, with agriculture accounting for the vast majority. And as we have seen recently with the severe drought in the US Midwest, and the floods in Asia, it would appear that climate change is having an effect on harvests that available water reserves cannot address.

Being able to measure the amount of water available and used is just one aspect of the problem. What is really needed is action that addresses the issue directly – something the global community has so far shown itself to be either too slow or ineffective in agreeing and organising.

Neil Eisberg - Editor

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