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 can produce food without oil, but not without 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, or 500 times as much. 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. It thus comes as no surprise that irrigation expansion has played a central role in tripling the world grain harvest over the last six decades.
During the last half of the twentieth century, the world’s irrigated area expanded from close to 250 million acres (100 million hectares) in 1950 to roughly 700 million in 2000. This near tripling of world irrigation within 50 years was historically unique. But since then the growth in irrigation has come to a near standstill, expanding only 10 percent between 2000 and 2010.
In looking at water and our future, we face many questions and few answers. Could the world be facing peak water? Or has it already peaked?
Farmers get their irrigation water either from rivers or from underground aquifers. Historically, beginning with the Sumerians some 6,000 years ago, irrigation water came from building dams across rivers, creating reservoirs that then enabled them to divert the water onto the land through a network of gravity-fed canals. This method of irrigation prevailed until the second half of the twentieth century, where with few sites remaining for building dams, the prospects for expanding surface irrigation faded. Farmers then turned to drilling wells to tap underground water resources.
In doing so, they learned that there are two types of aquifers: those that are replenishable through rainfall, which are in the majority, and those that consist of water laid down eons ago, and thus do not recharge. The latter, known as fossil aquifers, include two strategically important ones, the deep aquifer under the North China Plain and the Ogallala aquifer under the U.S. Great Plains.
Tapping underground water resources helped expand world food production, but as the demand for grain continued climbing, so too did the amount of water pumped. Eventually the extraction of water began to exceed the recharge of aquifers from precipitation, and water tables began to fall. And then wells begin to go dry. In effect, overpumping creates a water-based food bubble, one that will burst when the aquifer is depleted and the rate of pumping is necessarily reduced to the rate of recharge.
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. More
