Saturday, March 3, 2012

Humanity's Growing Impact on the World's Freshwater: Original from National Geographic's Water Currents / By Sandra Postel

Humanity's Growing Impact on the World's Freshwater

It takes water to make everything, and the explosion of demand for all manner of products is draining rivers, shrinking lakes and depleting aquifers. 

As the human population has climbed past seven billion, and the consumption per person of everything from burgers to blue jeans has risen inexorably, the finiteness of Earth’s freshwater is becoming ever more apparent.

It takes water to make everything, and the explosion of demand for all manner of products is draining rivers, shrinking lakes, and depleting aquifers.

Consider this: on average it takes 2,700 liters (713 gallons) to make a cotton shirt and 9,800 liters (2600 gallons) to make a pair of blue jeans.  The cotton crops growing in farmers’ fields consume most of that water; a smaller share is used in the factories that churn out the clothes.

On any given day we’re likely wearing more than 15,000 liters (~4,000 gallons) worth of water.  And if we slip on a pair of leather loafers, well, add another 8,000 liters (~2,100 gallons).  It takes a lot of water to grow the grain to feed the cow whose skin is turned into shoes.

Such figures might not matter if there was abundant water whenever and wherever we needed it – or if water had a substitute.  But water is limited, and there’s no substitute for it.  We need water to quench our thirst, to grow our food, to cool electric power plants, and to make cars, computers and all those cotton shirts.

And that’s why the size of humanity’s water footprint – and of yours and mine – matters.

In a study published this week in the Proceedings of the National Academy of Sciences, researchers Arjen Hoekstra and Mesfin Mekonnen of the University of Twente in the Netherlands, have made the most detailed estimate to date of the scale and patterns of humanity’s water consumption.

This is a tricky and complicated task.  Using a high level of spatial resolution, the researchers tabulated all the water from both rainfall and irrigation that’s consumed in making goods and services for the global population. To complete the picture, they added in the volume of water needed to assimilate the pollution generated along the way.  They calculated the annual average global footprint for 1996-2005, the most recent ten-year period for which the necessary data were available.

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