Drought, condition of abnormally dry weather within a geographic region where some rain might usually be expected. A drought is thus quite different from a dry climate which designates a region that is normally, or at least seasonally, dry.
The word drought is applied to a time where an unusual shortage of rain causes a serious hydrological imbalance: Water-supply reservoirs are empty, wells dry up, and crop damage ensues. The severity of the drought is determened by the degree of moisture deficiency, its lengh, and the size of the area affected. If the drought is short, it is known as a dry spell, or partial drought. A partial drought is usually defined as more than 14 days without a notable amount of precipitation, onthe other hand a drought may last for years.
Droughts tend to be more severe in some areas than in others. Catastrophic droughts generally occur at latitudes of about 15.-20. and in areas bordering the permanently arid regions of the world. Lands that are permanent arid is a characteristic of those areas where warm, tropical air masses, in descending to earth, become hotter and drier. When a poleward shift in the west ocurrs, the high-pressure, anticyclonic conditions of the permanently arid regions hit each other on areas that are normally used to seasonally wet low-pressure weather and a drought follows. A southward shift in the western winds causes the most severe drought of the 20th century, the one that struck the African region, Sahel for 12 years starting in 1968.
Statistics indicate that roughly every 22 years a major drought occurs in the United States, they affect the Prairie and midwestern states the most. The disastrous drought of 1933-35, during which large areas of the Great Plains became known as the Dust Bowl, is one example. The effect of the drought was caused cropping, overpopulation, and lack of timely relief measures. In Africa, the Sahel drought was also caused by nonclimate causes such as over cropping.
The types of droughts are Meterological, Agricultural, Hydrological, Sociologial, and Legislative. Meterological is when it doesn’t rain. Agricultural is when the sub soil is dry. Hydrological is when water sources are low. Sociologial is the result of both Meterological and Hydrological and often people are forced to move. Legislative is when the distribution of water is imposed by law.
Although drought cannot be depenenly predicted, certain steps can be taken in areas that risk drought. These include construction of reservoirs to hold emergency water supplies, education to avoid overcropping and overgrazing, and programs to limit settlement in drought areas.