Peak oil has generated headlines in recent years, but the real threat to our future is peak water. There are substitutes for oil, but not for water.
We drink on average four liters of water per day, in one form or another, but the food we eat each day requires 2,000 liters of water to produce. Getting enough water to drink is relatively easy, but finding enough to produce the ever-growing quantities of grain the world consumes is another matter.
Grain consumed directly supplies nearly half of our calories. That consumed indirectly as meat, milk, and eggs supplies a large part of the remainder. Today roughly 40 percent of the world grain harvest comes from irrigated land.
During the last half of the twentieth century, the world’s irrigated area expanded from close to 250 million acres in 1950 to roughly 700 million in 2000. But since then the growth in irrigation has come to a near standstill, expanding only 10 percent between 2000 and 2010.
Today some 18 countries, containing half the world’s people, are overpumping their aquifers. Among these are the big three grain producers—China, India, and the United States—and several other populous countries, including Iran, Pakistan and Mexico.
During the last couple of decades, some of these countries have overpumped to the point where aquifers are being depleted and wells are going dry. Several have passed not only peak water, but also the peak in grain production that often follows. Among the countries whose use of water has peaked and begun to decline are Saudi Arabia, Syria, Iraq, and Yemen. In each of these countries peak grain has followed peak water.
In summarizing prospects for the three big grain producers—the United States, China, and India—we see sharp contrasts. In the United States, the irrigated grainland is starting to shrink largely as a result of depletion of the Ogallala aquifer, making it more difficult to rapidly increase overall grain production.
China, with four fifths of its grain harvest coming from irrigated land, relies heavily on irrigation, but it is largely river water. A notable exception to this is the all-important North China Plain which relies heavily on underground water. With tight water supplies in northern China and with cities claiming more irrigation water, the shrinking water supply will likely reduce the harvest in some local situations. And before long it could more than offset production gains, leading to an absolute decline in China’s grain harvest.
Of the big three countries, India is the most vulnerable to overpumping. Three fifths of its grain harvest comes from irrigated land. And since only a minor share of its irrigation water comes from rivers, India is overwhelmingly dependent on underground water. Its millions of wells, each powered with a diesel engine or electric motor, are dropping water tables at an alarming rate. Accurate data are hard to come by, but India may have already passed peak water. The question is, will peak water be followed by peak grain or is there sufficient unrealized technological potential remaining to raise grain yields enough to offset any imminent losses from wells going dry?
The world has quietly transitioned into a situation where water, not land, has emerged as the principal constraint on expanding food supplies. As water tables fall and as wells go dry, world food prices are rising. This collision with the earth’s water limits underlines the urgency of not only halting population growth but stabilizing it at a size that is within the earth’s water limits.
The findings, interpretations, and conclusions expressed in this blog do not necessarily reflect the views of The World Bank, its Board of Executive Directors, or the governments they represent. The views here represent the views of the author.