Bone-dry China

Arid or semi-arid regions make up 58 percent of China's total landmass [source: Youlin et al.]. The growing population's demand for food and water has led to the desertification of approximately one-third of the land in these areas. As a result, dust storms have ravaged the country with increased frequency in the past decade. In response, China has followed the example of America's response to the Dust Bowl in the 1930s, and has implemented multiple national programs to protect and restore the dry lands used for agriculture.

Where Do Dust Storms Occur?

The erosion of soil in one area and deposition of it in another is a process that has played a role in our global ecosystem since time began. Although dust storms make headlines for the havoc they cause, their occurrence is not always a tale of destruction and mayhem. For instance, 20 million tons of dust are transported from the Bodele depression in the Sahara to the Amazon basin each year, supplying the rain forest with essential minerals and nutrients to keep it fertile and thriving [source: Koren].

From a small, cyclone-like burst of dust that only lasts for a few minutes to storms that blow dust for 50 days straight at near-hurricane speeds, dust storms result from a combination of climate, weather and wind. Central Asia, North America, Central Africa and Australia are home to the most dust storms, but they can kick up anywhere where the conditions are ripe.

The first element needed for any dust storm -- a source of dust -- depends largely on climate. Ideal dust sources occur in areas where the composition of the soil is very dry and loosely held on the surface. This most commonly occurs in arid and semi-arid regions, usually after a prolonged drought. Moisture keeps soil compact and helps maintain vegetation, which protects it from being swept up into passing winds. Not surprisingly, dust storms frequently occur in the desert. However, marginal dry lands are increasingly a source of major dust storms. These areas have fragile, delicately balanced ecosystems. Their degradation, called desertification, makes the soil less resilient to wind during prolonged drought. Desertification sometimes happens naturally; the Bodele Depression, for instance, is a natural dry lake bed that was once a large freshwater lake in northern Chad. Now, an average of 0.7 tons of dust a day is blown up from the dried up lake each winter [source: Koren].

Increasingly, however, desertification results from human activity. Excessive animal grazing, timber cutting and farming methods strip and exhaust dry-land topsoil. When a drought occurs in these areas -- and eventually it will -- all you need is the right weather and you've got yourself a dust storm.

So how do dust storms form? First, we'll examine how wind gets dust into the air and later find out how weather patterns determine what happens to the dust once it's airborne.