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Drought is not easily defined and often depends on who you speak to. The South African Weather Service defines drought on the basis of the degree of dryness in comparison to normal or average amounts of rainfall for a particular area or place and the duration of the dry period. This is what is termed a meteorological drought.
Less than 75% of normal rainfall is regarded as a severe meteorological drought but a shortfall of 80% of normal rainfall will cause crop and water shortages which will ultimately affect social and economic factors. Normal rainfall for a particular place is calculated over a 30-year period using for example rainfall figures from 1961 to 1990. Other climatic factors such as high temperature, high wind, low soil moisture and low relative humidity can significantly aggravate the severity of drought conditions and these additional factors should also be taking into account.