When there is a dry spell, grass begins to turn brown. Flowers need to be watered more frequently. Dirt patches dry up. Cracks form across the surface of the ground. After many weeks of such weather, plants die out. The roots of the plants, which previously anchored soil down, can no longer keep the soil from eroding. The dirt is then blown up by the wind, causing huge clouds known as dust storms. Because they can turn the sky dark, they are sometimes known as black blizzards.
Forces of Nature: ThinkQuest 2000 (Team #C003603)
http://library.thinkquest.org/C003603/english/droughts/whatsadrought.shtml
A drought occurs when there is not enough rain to support people or crops. In temperate regions, a drought is classified as 15 consecutive days with less than 0.01 inches (0.25 millimeters) of rain. During a drought, it still rains once in a while. However, storms or cloudbursts are brief and any precipitation that falls dries up quickly afterwards. Small droughts occur every now and then, and these are not particularly harmful. Most happen in the summer, when hot and dry weather is normal. However, sometimes droughts can occur of months, years, or even decades. When an area appears to suffer from dryness for thousands of years, the region is said to have a dry climate.