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.
Falling water tables are already adversely affecting harvests in some countries, including China, which rivals the United States as the world’s largest grain producer. A groundwater survey released in Beijing in August 2001 revealed that the water table under the North China Plain, an area that produces over half of the country’s wheat and a third of its corn, is falling fast. Overpumping has largely depleted the shallow aquifer, forcing well drillers to turn to the region’s deep aquifer, which is not replenishable.
The survey reported that under Hebei Province in the heart of the North China Plain, the average level of the deep aquifer was dropping nearly 3 meters (10 feet) per year. Around some cities in the province, it was falling twice as fast. As the deep aquifer is depleted, the region is losing its last water reserve—its only safety cushion.
A World Bank study indicates that China is mining underground water in three adjacent river basins in the north—those of the Hai, which flows through Beijing and Tianjin; the Yellow; and the Huai, the next river south of the Yellow. Since it takes 1,000 tons of water to produce one ton of grain, the shortfall in the Hai basin of nearly 40 billion tons of water per year (1 ton equals 1 cubic meter) means that when the aquifer is depleted, the grain harvest will drop by 40 million tons—enough to feed 120 million Chinese.
As serious as water shortages are in China, they are even more serious in India, where the margin between food consumption and survival is so precarious. To date, India’s 100 million farmers have drilled 21 million wells, investing some $12 billion in wells and pumps. In a survey of India’s water situation, Fred Pearce reported in New Scientist that “half of India’s traditional hand-dug wells and millions of shallower tube wells have already dried up, bringing a spate of suicides among those who rely on them.”
India’s grain harvest, squeezed both by water scarcity and the loss of cropland to non-farm uses, has plateaued since 2000. A 2005 World Bank study reports that 15 percent of India’s food supply is produced by mining groundwater. Stated otherwise, 175 million Indians are fed with grain produced with water from irrigation wells that will soon go dry.
In the United States, the U.S. Department of Agriculture (USDA) reports that in parts of Texas, Oklahoma, and Kansas—three leading grain-producing states—the underground water table has dropped by more than 30 meters (100 feet). As a result, wells have gone dry on thousands of farms in the southern Great Plains, forcing farmers to return to lower-yielding dryland farming. Although this mining of underground water is taking a toll on U.S. grain production, irrigated land accounts for only one fifth of the U.S. grain harvest, compared with close to three fifths of the harvest in India and four fifths in China.
Pakistan, a country with 164 million people, is also mining its underground water. Observation wells near the twin cities of Islamabad and Rawalpindi in the fertile Punjab plain show a fall in the water table between 1982 and 2000 that ranges from 1 to nearly 2 meters a year. In the province of Balochistan, which borders Afghanistan, water tables around the capital, Quetta, are falling by 3.5 meters per year. Throughout the province, six basins have exhausted their groundwater supplies, leaving their irrigated lands barren. Sardar Riaz A. Khan, former director of Pakistan’s Arid Zone Research Institute, expects that within 10–15 years virtually all the basins outside the canal-irrigated areas will have depleted their groundwater supplies, depriving the province of much of its grain harvest.
Iran, a country of 71 million people, is overpumping its aquifers by an average of 5 billion tons of water per year, the water equivalent of one third of its annual grain harvest. Under the small but agriculturally rich Chenaran Plain in northeastern Iran, the water table was falling by 2.8 meters a year in the late 1990s. New wells being drilled both for irrigation and to supply the nearby city of Mashad are responsible. Villages in eastern Iran are being abandoned as wells go dry, generating a flow of “water refugees.”
Saudi Arabia, a country of 25 million people, is as water-poor as it is oil-rich. Relying heavily on subsidies, it developed an extensive irrigated agriculture based largely on its deep fossil aquifer. After several years of supporting wheat prices at five times the world market level, the government was forced to face fiscal reality and cut the subsidies. Its wheat harvest dropped from a high of 4.1 million tons in 1992 to 2.7 million tons in 2007, a drop of 34 percent. Some Saudi farmers are now pumping water from wells that are 4,000 feet deep, nearly four fifths of a mile or 1.2 kilometers. Recognizing its hydrologic limitations, in early 2008 the Saudi government announced plans to phase out wheat production entirely by 2016.
In neighboring Yemen, a nation of 22 million, the water table under most of the country is falling by roughly 2 meters a year as water use outstrips the sustainable yield of aquifers. In western Yemen’s Sana’a Basin, the estimated annual water extraction of 224 million tons exceeds the annual recharge of 42 million tons by a factor of five, dropping the water table 6 meters per year. World Bank projections indicate the Sana’a Basin—site of the national capital, Sana’a, and home to 2 million people—may be pumped dry by 2010.
With its population growing at 3 percent a year and with water tables falling everywhere, Yemen is fast becoming a hydrological basket case. With its grain production falling by two thirds over the last 20 years, Yemen now imports four fifths of its grain supply.
Since the overpumping of aquifers is occurring in many countries more or less simultaneously, the depletion of aquifers and the resulting harvest cutbacks could come at roughly the same time. And the accelerating depletion of aquifers means this day may come soon, creating potentially unmanageable food scarcity.