http://www.eoearth.org/article/Aquifer_depletionAquifer depletion
Lead Author: Lester Brown (other articles)
Article Topics: Environmental history,
Water,
Agriculture and food and
Ground water management
This article has been reviewed and approved by the following Topic Editors: Brian Black (other articles) and
Galal Hassan Galal Hussein (other articles)
Last Updated: February 12, 2007
Scores of countries are overpumping
aquifers as they struggle to satisfy their growing water needs, including each of the big three grain producersChina, India, and the United States. These three, along with a number of other countries where water tables are falling, are home to more than half the worlds people. (See Table at end of article.)
There are two types of
aquifers: replenishable and nonreplenishable (or fossil) aquifers. Most of the aquifers in India and the shallow aquifer under the North China Plain are replenishable. When these are depleted, the maximum rate of pumping is automatically reduced to the rate of recharge.
For fossil aquiferssuch as the vast U.S. Ogallala aquifer, the deep aquifer under the North China Plain, or the Saudi aquiferdepletion brings pumping to an end. Farmers who lose their irrigation water have the option of returning to lower-yield dryland farming if rainfall permits. In more arid regions, however, 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, the worlds largest grain producer. A
groundwater survey released in Beijing in August 2001 revealed that the water table under the North China Plain, which produces over half of that countrys wheat and a third of its corn, is falling faster than earlier reported. Overpumping has largely depleted the shallow aquifer, forcing well drillers to turn to the regions deep fossil aquifer, which is not replenishable.
The survey, conducted by the Geological Environmental Monitoring Institute (GEMI) in Beijing, 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. He Qingcheng, head of the GEMI groundwater monitoring team, notes that as the deep aquifer is depleted, the region is losing its last water reserveits only safety cushion.
He Qingcheng's concerns are mirrored in a World Bank report: Anecdotal evidence suggests that deep wells [drilled] around Beijing now have to reach 1,000 meters [more than half a mile] to tap fresh water, adding dramatically to the cost of supply. In unusually strong language for a Bank report, it foresees catastrophic consequences for future generations unless water use and supply can quickly be brought back into balance.
The U.S. embassy in Beijing reports that wheat farmers in some areas are now pumping from a depth of 300 meters, or nearly 1,000 feet. Pumping water from this far down raises pumping costs so high that farmers are often forced to abandon irrigation and return to less productive dryland farming.
Falling water tables, the conversion of cropland to nonfarm uses, and the loss of farm labor in provinces that are rapidly industrializing are combining to shrink Chinas grain harvest. The wheat crop, grown mostly in semiarid northern China, is particularly vulnerable to water shortages. After peaking at 123 million tons in 1997, the harvest has fallen in five of the last eight years, coming in at 95 million tons in 2005, a drop of 23 percent.
The U.S. embassy also reports that the recent decline in rice production is partly a result of water shortages. After peaking at 140 million tons in 1997, the harvest dropped in four of the following eight years, falling to an estimated 127 million tons in 2005. Only corn, Chinas third major grain, has thus far avoided a decline. This is because corn prices are favorable and because the crop is not as irrigation-dependent as wheat and rice are.
Overall, Chinas grain production has fallen from its historical peak of 392 million tons in 1998 to an estimated 358 million tons in 2005. For perspective, this drop of 34 million tons exceeds the annual Canadian wheat harvest. China largely covered the drop-off in production by drawing down its once vast stocks until 2004, at which point it imported 7 million tons of grain.
A World Bank study indicates that China is overpumping three river basins in the north-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.
Of the leading grain producers, only China has thus far experienced a substantial decline in production. Even with a worldwide grain crunch and climbing grain prices providing an incentive to boost production, it will be difficult for China to regain earlier grain production levels, given the loss of irrigation water.
Serious though emerging water shortages are in China, they are even more serious in India simply because the margin between actual food consumption and survival is so precarious. In a survey of Indias water situation, Fred Pearce reported in the
New Scientist that the 21 million wells drilled in this global epicenter of well-drilling are lowering water tables in most of the country. In North Gujarat, the water table is falling by 6 meters (20 feet) per year.
In Tamil Nadu, a state with more than 62 million people in southern India, wells are going dry almost everywhere. According to Kuppannan Palanisami of Tamil Nadu Agricultural University, falling water tables have dried up 95 percent of the wells owned by small farmers, reducing the irrigated area in the state by half over the last decade.
As water tables fall, well drillers are using modified oil-drilling technology to reach water, going as deep as 1,000 meters in some locations. In communities where underground water sources have dried up entirely, all agriculture is rain-fed and drinking water is trucked in. Tushaar Shah, who heads the International Water Management Institutes groundwater station in Gujarat, says of Indias water situation: When the balloon bursts, untold anarchy will be the lot of rural India.
At this point, the harvests of wheat and rice, Indias principal food grains, are still increasing. But within the next few years, the loss of irrigation water could override technological progress and start shrinking the harvest in some areas, as it is already doing in China.
In the United States, the 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. 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 158 million people that is growing by 3 million per year, is also mining its underground water. In the Pakistani part of the fertile Punjab plain, the drop in water tables appears to be similar to that in India. Observation wells near the twin cities of Islamabad and Rawalpindi 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 Baluchistan, water tables around the capital, Quetta, are falling by 3.5 meters per year. Richard Garstang, a water expert with the World Wildlife Fund and a participant in a study of Pakistans water situation, said in 2001 that within 15 years Quetta will run out of water if the current consumption rate continues.
The water shortage in Baluchistan is province-wide. Sardar Riaz A. Khan, former Director of Pakistans Arid Zone Research Institute in Quetta, reports that six basins have exhausted their
groundwater supplies, leaving their irrigated lands barren. Khan expects that within 1015 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.
Future irrigation water cutbacks as a result of
aquifer depletion will undoubtedly reduce Pakistans grain harvest. Countrywide, the harvest of wheat-the principal food staple-is continuing to grow, but more slowly than in the past.
Iran, a country of 70 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 using oil money to support 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 1.2 million tons in 2005, a drop of 71 percent.
Craig Smith writes in the
New York Times, From the air, the circular wheat fields of this arid lands breadbasket look like forest green poker chips strewn across the brown desert. But they are outnumbered by the ghostly silhouettes of fields left to fade back into the sand, places where the kingdoms gamble on agriculture has sucked precious aquifers dry. Some Saudi farmers are now pumping water from wells that are 4,000 feet deep, nearly four-fifths of a mile (1 mile equals 1.61 kilometers).
Countries Overpumping Aquifers in 2005 Country Population
(million) China 1,316 India 1,103 Iran 70 Israel 7 Jordan 6 Mexico 107 Morocco 31 Pakistan 158 Saudi Arabia 25 South Korea 48 Spain 43 Syria 19 Tunisia 10 United States 298 Yemen 21
Total 3,262 A 1984 Saudi national survey reported fossil water reserves at 462 billion tons. Half of that, Smith reports, has probably disappeared by now. This suggests that irrigated agriculture could last for another decade or so and then will largely vanish, limited to the small area that can be irrigated with water from the shallow
aquifers that are replenished by the kingdoms sparse rainfall. It is a classic example of an overshoot-and-collapse food economy.
In neighboring Yemen, a nation of 21 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 Yemens Sanaa 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 Sanaa Basin-site of the national capital, Sanaa, and home to 2 million people-will be pumped dry by 2010.
In the search for water, the Yemeni government has drilled test wells in the basin that are 2 kilometers (1.2 miles) deep-depths normally associated with the oil industry-but they have failed to find water. Yemen must soon decide whether to bring water to Sanaa, possibly by pipeline from coastal desalting plants, if it can afford it, or to relocate the capital. Either alternative will be costly and potentially traumatic.
With its population growing at 3 percent a year and with water tables falling everywhere, Yemen is fast becoming a hydrological basket case. Aside from the effect of overpumping on the capital, World Bank official Christopher Ward observes that groundwater is being mined at such a rate that parts of the rural economy could disappear within a generation.
Israel, even though a pioneer in raising irrigation water productivity, is depleting both of its principal aquifers-the coastal aquifer and the mountain aquifer that it shares with Palestinians. Israels population, whose growth is fueled by both natural increase and immigration, is outgrowing its water supply. Conflicts between Israelis and Palestinians over the allocation of water in the latter area are ongoing. Because of severe water shortages, Israel has banned the irrigation of wheat.
In Mexico-home to a population of 107 million that is projected to reach 140 million by 2050-the demand for water is outstripping supply. Mexico Citys water problems are well known and rural areas are also suffering. For example, in the agricultural state of Guanajuato, the water table is falling by 2 meters or more a year. At the national level, 51 percent of all the water extracted from underground is from
aquifers that are being overpumped.
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.
