Many countries are facing dangerous water shortages. As world demand for food has soared, millions of farmers have drilled too many irrigation wells in efforts to expand their harvests. As a result, water tables are falling and wells are going dry in some 20 countries containing half the world’s people. The overpumping of aquifers for irrigation temporarily inflates food production, creating a food production bubble that bursts when the aquifer is depleted.
The shrinkage of irrigation water supplies in the big three grain-producing countries—the United States, India, and China—is of particular concern. Thus far, these countries have managed to avoid falling harvests at the national level, but continued overexploitation of aquifers could soon catch up with them.
In most of the leading U.S. irrigation states, the irrigated area has peaked and begun to decline. In California, historically the irrigation leader, a combination of aquifer depletion and the diversion of irrigation water to fast-growing cities has reduced irrigated area from nearly 9 million acres in 1997 to an estimated 7.5 million acres in 2010. (One acre equals 0.4 hectares.) In Texas, the irrigated area peaked in 1978 at 7 million acres, falling to some 5 million acres as the Ogallala aquifer underlying much of the Texas panhandle was depleted.
Other states with shrinking irrigated area include Arizona, Colorado, and Florida. All three states are suffering from both aquifer depletion and the diversion of irrigation water to urban centers. And now that the states that were rapidly expanding their irrigated area, such as Nebraska and Arkansas, are starting to level off, the prospects for any national growth in irrigated area have faded. With water tables falling as aquifers are depleted under the Great Plains and California’s Central Valley, and with fast-growing cities in the Southwest taking more and more irrigation water, the U.S. irrigated area has likely peaked.