(This is Part 5 of a continuing series. Go back to Part 4.)
The Great Plains of the United States is the world's bread basket. Half of all the grain exported in the entire world comes from the U.S. Great Plains.
Beneath the Great Plains is a vast underground reservoir of water called the Ogallala Aquifer, laid down through eons of geological time. Water drawn from this aquifer through millions of wells has helped to greatly increase grain yields in the last half century because the water can irrigate crops whenever and wherever desired.
Similarly, there are vast underground aquifers beneath the farmlands of China and India—who along with the U.S. account for half the grain grown on the planet—as well as in many other countries around the world.
The experience in the United States is being replicated in these other countries. That is, water from these gigantic aquifers has been tapped in the last 50 years to greatly increase crop yields worldwide, particularly on lands that are dry or somewhat dry.
However, there's a catch. The increased use of electric and diesel pumps since 1950 has hugely increased the amount of water that can be brought to the surface, but in doing so the amount of water in these deep aquifers has been dropping.
The overpumping of aquifers has resulted in falling water tables worldwide. For instance, the average level of the water in the aquifer under the North China Plain is falling, by some estimates, at 10 feet a year. Wheat farmers in China are having to drill wells of 1000 feet or more. Wells around Beijing now have to be drilled over half a mile down to reach fresh water.
In India and the United States the story is the same. The water table in Gujarat, for example, has fallen from 15 meters to 400 meters in the last 30 years. In the United States wells on thousands of farms in the southern Great Plains have gone dry.
The thing is, in many cases it's simply not known how deep these vast "fossil" aquifers are. Thus their depletion could come very suddenly and unexpectedly, particularly given the huge rate at which they are being depleted worldwide.
Whenever this aquifer depletion happens it is certain to drastically lower crop yields worldwide, because crops are heavily dependent on water. For example, it takes about 1000 tons of water to grow one ton of grain.
Now let's step back again for a moment: We see the world drawing from deep aquifers in order to gain greater crop yields. Greater yields are the immediate, primary effect.
But underneath the surface something else is happening—the depletion of the aquifers on a global scale. Because high-yield crops depend tremendously on irrigated water and because the deep aquifers cannot be replenished once gone, when they do become depleted a precipitous decline in crop yields will almost certainly follow—the opposite, long-lasting and secondary effect.
(This is the end of Part 5. Go to Part 6.)
—jim sloman, 9.20.04 for Feb 6
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