Scores of countries are overpumping aquifers as they struggle to satisfy their growing water needs. The drilling of millions of irrigation wells has pushed water withdrawals beyond recharge rates, in effect leading to groundwater mining. The failure of governments to limit pumping to the sustainable yield of aquifers means that water tables are now falling in countries that contain more than half the world’s people, including the big three grain producers—China, India, and the United States.

Most of the world’s aquifers are replenishable, so that when they are depleted, the maximum rate of pumping will be automatically reduced to the rate of recharge. Fossil aquifers, however, are not replenishable. For these—including the vast U.S. Ogallala aquifer, the deep aquifer under the North China Plain, or the Saudi aquifer, for example—depletion brings pumping to an end. Farmers who lose their irrigation water have the option of returning to lower-yield dryland farming if rainfall permits. But in more arid regions, such as in the southwestern United States or the Middle East, the loss of irrigation water means the end of agriculture.

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