Virtual Water

Close on the heels of the carbon footprint comes the concept of virtual water, as explained by Fred Pearce in an article in NewScientist.

... The term was the invention of water scientist Tony Allan from King's College London [winner of the 2008 Stockholm Water Prize] and, I think, it goes a long way to explaining why the world is currently in the grips of a food crisis.

Most crops take extraordinary amounts of water to grow: a thousand tonnes for a tonne of wheat, for instance. In fact, two-thirds of all the water abstracted from the world's rivers and underground reserves goes for crop irrigation. Unsurprisingly, dry countries, like most of the Middle East, don't have enough water to feed their growing populations.

So they import water. They import virtual water. This trade is huge, the equivalent of 20 times the flow of the world's longest river, the Nile...

Meanwhile global demand for virtual water is soaring, especially from China, where water is the main constraint on food production. China has effectively run out of water in its traditional breadbasket region in the north of the country, where the Yellow River now rarely reaches the sea in any volume. China can't feed itself any more...

In another article, NewScientist has one of those graphics that are worth a thousand words.