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Falling water tables threatens grain harvests and agriculture worldwide

Posted by: Aqua Blog Maven on May 12, 2008 at 6:04 am

From People and Planet:

As China’s farmers sink their pumps ever lower and aquifers begin to run dry grain harvests could be in serious trouble says Lester Brown in this wide-ranging report on the problem.

As the world’s demand for water has tripled over the last half-century and as the demand for hydroelectric power has grown even faster, dams and diversions of river water have drained many rivers dry. As water tables fall, the springs that feed rivers go dry, reducing river flows. Scores of countries are overpumping aquifers as they struggle to satisfy their growing water needs, including each of the big three grain producers - China, India, and the United States. More than half the world’s people live in countries where water tables are falling.

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 aquifers, such as the vast US Ogallala aquifer, the deep aquifer under the North China Plain, or the Saudi aquifer, 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. 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.

The article discusses water use and shortages from around the world, including the U.S.:

While falling water tables are largely hidden, rivers that are drained dry before they reach the sea are highly visible. Two rivers where this phenomenon can be seen are the Colorado, the major river in the southwestern United States, and the Yellow, the largest river in northern China. Other large rivers that either run dry or are reduced to a mere trickle during the dry season are the Nile, the lifeline of Egypt; the Indus, which supplies most of Pakistan’s irrigation water; and the Ganges in India’s densely populated Gangetic basin. Many smaller rivers have disappeared entirely.

Since 1950, the number of large dams, those over 15 meters high, has increased from 5,000 to 45,000. Each dam deprives a river of some of its flow. Engineers like to say that dams built to generate electricity do not take water from the river, only its energy, but this is not entirely true since reservoirs increase evaporation. The annual loss of water from a reservoir in arid or semiarid regions, where evaporation rates are high, is typically equal to 10 percent of its storage capacity.

The Colorado River now rarely makes it to the sea. With the states of Colorado, Utah, Arizona, Nevada, and, most important, California depending heavily on the Colorado’s water, the river is simply drained dry before it reaches the Gulf of California. This excessive demand for water is destroying the river’s ecosystem, including its fisheries.

Read more from People and Planet by clicking here.

May 12, 2008 · Filed Under International Water Issues

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