Groundwater loss in cubic liters per year…..Credit: American Geophysical Union
Of the most useful water for humans, groundwater – water that flows or resides underground – comprises about 30% of the total. Another 1% is surface water. The rest is water locked in glaciers and polar ice caps. As you might expect, it’s difficult to take an inventory of groundwater. A new study, led by Marc Bierkens of Utrecht University (Netherlands) and published in the American Geophysical Union journal Geophysical Research Letters has made a concerted effort to make accurate estimates of the groundwater supply and the rate at which it is depleted. The results, like similar studies of fresh water resources, are unsettling in their implications. Quite simply, we – the human population – are using groundwater faster than it is replenished.
The study was built on figures that, on the one hand, added up the precipitation figures in regions throughout the world and on the other, the amounts being withdrawn for agricultural and human consumption. From the available data, which admittedly is not complete for all parts of the world, they built a model that included factors such as evaporation, geology, and climate variation. Applying this model to key regions, the research team found the rate of groundwater depletion doubled between 1960 and 2000. The rate increased in a linear fashion (no interruptions). Because of the intense use of water by rapidly developing giant countries such as China, India, and Brazil; the rate of water depletion is not likely to decrease. The loss in the forty years covered by the study was estimated to be between 126 to 283 cubic kilometers (30-68 cubic miles) of water per year. For perspective this rate of loss would leave the Great Lakes of the United States and Canada dry in 80 years.
Soaring global groundwater depletion bodes a potential disaster for an increasingly globalized agricultural system, says Marc Bierkens of Utrecht University in Utrecht, the Netherlands, and leader of the new study.
“If you let the population grow by extending the irrigated areas using groundwater that is not being recharged, then you will run into a wall at a certain point in time, and you will have hunger and social unrest to go with it,” Bierkens warns. “That is something that you can see coming for miles.”
[Source: American Geophysical Union]
I doubt this comes as a surprise. Droughts are common enough in human history. The idea that major population centers might be running out of easily accessible fresh water has been floating (if that’s the word) around for decades. Intuitively it’s easy enough to understand that water is a finite commodity. Still we do little about it. Water conservation is no more thoroughly observed than energy conservation. Perhaps people feel that we’ll always discover more groundwater, or that technology will solve the problem of desalinating ocean water. Technology might do that, but rest uneasily because it will be costly. Most water now is ‘free’ – rain is totally free, of course. Pumping and piping water costs something, but nothing compared to what it will cost if we are forced to desalinate seawater.
Meanwhile we are building up a dependence on virtual water. This is an interesting concept that conservationists are beginning to use as a means of explaining how areas with adequate water supply will trade their water – mostly in the form of agricultural products – to areas that are short of water. Water is shipped around not in bulk form but incorporated in the production process – virtual water.
In a study by Paolo D’Odorico of the University of Charlottesville (North Carolina, USA) [Does globalization of water reduce societal resilience to drought?, AGU: Journal of Geophysical Research Letters, July, 2010] his team modeled a world increasingly dependent on a globalized water supply. They reported that the global transport of ‘virtual water’ has sustained the current population growth and is apparently efficient. However – and this is a very big however – the end result of virtual water transactions is an economy based on water debt, the water resources that are not replenished. This is particularly true in areas of the world responsible for much of the surplus agricultural output: The American midwest, California’s central valley, China’s northeast, northwest India. This makes the world economy more vulnerable to shocks from major droughts and crop failures. By analogy this is not unlike the developed world spending itself into debt to raise its standard of living – and then facing the (inevitable) contraction(s).
Yes, we have heard this story before. Debt. Oil. Water. What else?