A Drought is an extended period where water availability falls below the statistical requirements for a region. Drought is not a purely physical phenomenon, but instead is an interplay between natural water availability and human demands for water supply.
The precise definition of drought is made complex due to political considerations, but there are generally three types of conditions that are referred to as drought.
- Meteorological drought is brought about when there is a prolonged period with below average precipitation.
- Agricultural drought is brought about when there is insufficient moisture for average crop or range production. This condition can arise, even in times of average precipitation, due to soil conditions or agricultural techniques.
- Hydrologic drought is brought about when the water reserves available in sources such as aquifers, lakes, and reservoirs falls below the statistical average. This condition can arise, even in times of average (or above average) precipitation, when increased usage of water diminishes the reserves.
When the word "drought" is used commonly, the most often intended definition is meteorological drought. However, when the word is used by urban planners, it is more frequently in the sense of hydrologic drought.
Periods of drought can have significant economic and social consequences. The most famous example of this was seen in the dustbowl of the 1920s and 1930s, when entire districts of the American Great Plains were depopulated by a combination of drought and economic recession.
Drought can often be the precipitating factor that causes famine, in particular in countries without extensive economic resources.
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