Battling Drought: The Science of Water Management

Investments in the development of water resources have rarely exceeded 1 or 2 percent of the gross national product. In most countries they cannot be raised much above that level without causing hardship elsewhere in the economy. Capital is a resource in shorter supply than water, and the same strategies must be adopted for its conservation.

Egyptian records show an average of one plague every 11 years.

holdings ; land-rental and taxation systems that destroy incentive; extreme difficulties in obtaining a farm loan promptly at a reasonable interest rate; poor marketing and storage systems; administrative inefficiency and corruption; the shortage of trained teachers and farm advisers; inadequate government services for agricultural research, educat

When irrigation is combined with other practices for increasing the efficiency of agriculture, such as the planting of improved crop varieties and the application of fertilizer and pesticide, yields can be increased by a factor of three or four.

Even agriculture, man's principal consumer of water, takes little of the available supply. A billion acre-feet per year—less than 4 per cent of the total river flow—is used to irrigate 310 million acres of land, or about 1 per cent of the

few industries account for some two-thirds of all the demand: they are metals, chemicals and petroleum refining, pulp and paper manufacturing and food processing.

The total amount of rain and snow falling on the earth each year is about 380 billion acre-feet: 300

Wheat, rice and cotton fiber respectively require about 1,500, 4,000 and 10,000 tons of water per ton of crop.

Leaving crop residue in the field can reduce moisture loss by the equivalent of an inch or more of rainfall annually, scientists say. Funk