Answer: A drought is a period of drier-than-normal conditions that results in water-related problems. Precipitation (rain or snow) falls in uneven patterns across the country. The amount of precipitation at a particular location varies from year to year, but over a period of years, the average amount is fairly constant. In the deserts of the Southwest, the average precipitation is less than 3 inches per year. In contrast, the average yearly precipitation in the Northwest is more than 150 inches.
The amount of rain and snow also varies with the seasons. In some areas, most of the yearly precipitation falls in the early spring. In the Southeast, most of the yearly precipitation falls during the hurricane season in late summer and fall. Even if the total amount of rainfall for a year is about average, rainfall shortages can occur during a period when moisture is critically needed for plant growth.
When no rain or only a very small amount of rain falls, soils can dry out and plants can die. When rainfall is less than normal for several weeks, months, or years, the flow of streams and rivers declines, water levels in lakes and reservoirs fall, and the depth to water in wells increases. If dry weather persists and water-supply problems develop, the dry period can become a drought.
Reference: Moreland, 1993, Drought: U.S. Geological Survey Water Fact Sheet, Open-File Report 93-642, 2
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