An extended period of dry weather, generally associated with a blocking anticyclone in which evapotranspiration exceeds precipitation, causing soil moisture deficits. Some regions, especially arid and semi-arid areas, are particularly prone to droughts, which can result in food shortages and human suffering. In the Sahel region on the S edge of the Sahara Desert, rainfall 19681972 was only 50% of the 193160 average, and was accompanied by major famine. Other areas prone to drought include the W and mid-W USA, parts of Australia and S Africa, but it can occur in any place where there is a low rainfall, including Britain.
A drought is a period of time when there is not enough water to support agricultural, urban or environmental water needs. A drought usually refers to an extended period of below-normal rainfall, but can also be caused by drying bores or lakes, or anything that reduces the amount of liquid water available. Although what is considered "normal" varies from one region to another, drought is a recurring feature of nearly all the world's climatic regions. The effects of drought vary greatly, depending on agricultural, urban and environmental water needs.
Definitions
Conceptually, there are four main types of drought:
Meteorological drought is brought about when there is a prolonged period with less than average precipitation. Meteorological drought usually precedes the other kinds of drought.Decision makers at all levels need to decide ahead of time on an operational definition of drought that is relevant for their circumstances, and what actions they will take when they are in a drought.
Consequences
Periods of drought can have significant environmental, economic and social consequences. Loss of agricultural production Disease Thirst Famine due to lack of water for irrigation Social unrest Migration or relocation of those impacted War for water and foods. For example, subsistence farmers are more likely to migrate during drought because they don't have alternative food sources. Drought is rarely if ever the sole cause of famine;
Drought can also reduce water quality, because lower water flows reduce dilution of pollutants and increase contamination of remaining water sources.
Famous droughts
18th and 19th centuries, Cape Verde
Three droughts were responsible for over 100,000 starvation deaths.
1900, India
250,000 to 3.25 million died from drought, starvation and disease.
1921-22, Soviet Union
In the Ukraine and Volga regions, 250,000 to 5 million perished from starvation due to drought.
1928-30, northwest China
Famine resulted in over 3 million deaths.
1936, Sichuan Province, China
This was the worst drought in the modern history of the area.
1930-37, United States and Canada
Three waves of drought during this time are collectively referred to as "the Dust Bowl". Because of several factors including the coincidence of the dustbowl and the Great Depression, this drought had a severe impact on the U.S. and Canada, resulting in entire districts of the American and Canadian Great Plains being depopulated as people were forced to leave.
1941, Sichuan Province, China
This was less severe than the 1936 drought, and resulted in the deaths of only 2.5 million. However, because of the war with Japan at the time, the drought may be indirectly linked to many other deaths.
Current significant droughts
Australia
Much of Australia has typically low rainfall and drought is defined as rainfall in the lowest ten percent of records.
China
In August 2006, Chongqing Municipal and part of Sichuan Province experienced the most severe drought in recorded climate history of People's Republic of China.
The city area of Chongqing Municipal was the worst hit.
There is still no evidence showing any correlations of the drought with the building of Three Gorges Dam.
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