Drought is a condition of moisture deficit sufficient to have an adverse effect on vegetation, animals, and man over a sizeable area. The following questions and answers provide background on some of the scientific issues regarding drought. For questions on regulatory issues, such as water-use restrictions in states and localities, please refer to the appropriate authority in your jurisdiction. Questions and answers are original compositions or are compiled from any available sources and credit is given where appropriate. New material will be added as needed.
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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.