Large commercial grain farms are particularly susceptible to drought. A recent Newsweek article mapped a region of an extended drought that encompasses much of the U.S. Corn Belt.

A heavy May thunderstorm raked parts of the Corn Belt, but did little to increase soil moisture or provide drought relief. Farmers throughout the Midwest are reminded of the largest and deepest drought this country has ever seen. Thoughts of the 1930s Dust Bowl still chill farmers across the U.S. Interior Lowlands and the Great Plains.

Prolonged periods with less than normal precipitation and bright, clear and windy days are the farmer's bane. A drought occurs when soil moisture is depleted through evaporation and evapotranspiration by plants. Curling leaves and wilting plants are evidence of insufficient soil moisture, resulting in stunted plants and decreased crop yields.

A major axiom of climatology is, "The lower the average of annual precipitation, the less predictable is precipitation." In other words, desert rainfall is among the world's least predictable.

Any region can experience a drought. The U.S. Great Plains is a semi-arid grassland and periodic drought is expected. But in the glory years following World War I, much of the Great Plains' grasslands came under the plow. Particularly vulnerable was a region that centered on the Oklahoma panhandle, including eastern Colorado and New Mexico, western Oklahoma and Kansas, and panhandle Texas. This became known as the Dust Bowl.

Two important developments between 1917 and 1928 ultimately led to the Dust Bowl. First, the primitive armored tanks used in World War I provided technology for development of powerful tractors that could pull massive gangplows. Secondly, the end of the war brought an expanding and inflationary world economy with many Europeans to feed and clothe.

Although the normal annual precipitation was only about 20 inches (51 cm) in the southern Great Plains, during the 1920s the region received up to 30 inches (76 cm) annually. Section after section of natural grassland, locally called prairie, was plowed under from horizon to horizon. A section is a square mile, or 640 acres.

Wheat and cotton were planted on huge acreages of this marginal cropland. Rising inflation sent some land values from $5 per acre to more than $20. Farmers mortgaged their farms to purchase more farm machinery and more acreage. The world economy seemed limitless, but disaster loomed.

Wall Street crashed in 1929 and, so too, did the economy. World markets for wheat and cotton dried up. Then drought struck in 1932. Where crops grew luxuriantly a few years before, the ground was barren. In some places, precipitation dropped to less than half its normal average.

As banks foreclosed on farms, a wave of landless farm and tenant farm families left the region. John Steinbeck's The Grapes of Wrath describes the plight of the "Okies" in vivid detail as they left the Dust Bowl's terrible blowing dust in a hapless, desperate exodus for California.

At the height of the drought's unceasing winds, topsoil exposed by the plow was no longer anchored by the deep-rooted native bunch grasses. Dust blew into everything, into houses, beds and food. Crops from seeds that germinated were cut off at ground level by the blowing soil.

When the drought finally broke in 1938, farmers realized that such droughts were cyclic and would return. The few farmers who stayed watched the few areas of unplowed grass withstand the drought. They adopted soil and moisture conserving techniques of strip-cropping and windbreaks, planting cover crops and plowing small fields rather than large acreages.

Such lessons are not entirely lost on other agricultural regions around the country. Although few regions are as susceptible to these cyclic droughts as are the Great Plains, droughts do occasionally visit the more humid Corn Belt and even the Southeast.

While the Corn Belt contained many diversified farms through the 1950s, most of the region's farms are now commercial grain farms. Diversified farms had dairy and beef cattle, hogs and poultry and often depended upon several crops 50 years ago. Today's commercial grain farm, however, is likely to depend entirely upon one or two crops, leaving profits vulnerable to disease and commodity prices, not to mention drought.

The Corn Belt's current drought is severe enough to deeply concern farmers. They know that disaster lurks always in the fickleness of precipitation for the farming profession.