Drought
A drought is an abnormally dry period 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 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.
Encyclopedia
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drought is an abnormally dry period 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 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.
- Agricultural
...
drought is brought about when there is insufficient moisture for crop or range production. This condition can arise, even in times of average precipitation, owing to soil conditions or agricultural techniques.
- Physiological drought is a condition afflicting plants that have been exposed to too much salt, preventing them from absorbing water from soil. It is not related to climatological drought.
- Hydrological 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 precipitation, when increased usage of water diminishes the reserves.
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. Decision-makers include homeowners, farmers and ranchers, urban water suppliers, and policy makers. Each has different options and constraints.
Consequences
Periods of drought can have significant environmental, economic and social consequences. The most common consequences are:
The effect varies according to vulnerability. For example, subsistence farmers are more likely to migrate during drought because they don't have alternative food sources. Areas with populations that depend on subsistence farming as a major food source are more vulnerable to drought-triggered famine. Drought is rarely if ever the sole cause of famine; socio-political factors such as extreme widespread poverty play a major role.
Drought can also reduce water quality, because lower water flows reduce dilution of pollutants and increase
contamination of remaining water sources.
See also:
Aqueduct and trasvasement.
Famous droughts
Three droughts were responsible for over 100,000 starvation deaths. These droughts spurred the migration of much of the population to locations such as
New England, to participate in the
whaling industry.
250,000 to 3.25 million die from drought, starvation and disease.
In the
Ukraine and
Volga regions, 250,000 to 5 million perished from starvation due to drought. In contrast, the
Holodomor famine of 1932-33 in the same region was due to policies implemented under Stalin.
1928-30, northwest China
Famine resulted in over 3 million deaths.
This was the worst drought in the modern history of the area. 34 million farmers were displaced and 5 million people starved.
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.
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
In the past five to ten years major drought has struck large parts of Australia and for the first time it has begun to affect the urban population. Desalination projects have been initiated in
Sydney and the
Gold Coast. Many regions have placed heavy restrictions on water usage and some towns have been forced to import water.
Toowoomba in Queensland has voted on, and rejected, a referendum on using recycled sewage water.
Brisbane is set to be supplied via larger dams, a pipeline and possibly also recycling.
The current drought has affected more than three-quarters of the country. Because of the long-term effects of the drought now showing, many governments are now drought-proofing their areas not just for now, but for future generations. It has changed the way Australia treats its water resources. Australia in the past hundred years has relied solely on water from dams for agriculture and consumption. Now schemes like water-recycling, home water tank rebates and tougher restrictions on industries have come into effect.
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. On Aug 15, 2006, the Meteorology Bureau of Chongqing recorded a temperature of 44.5
°C, the highest since China began weather recording in 1891.
The city area of Chongqing Municipal was the worst hit. 21 million people and 20 million
mu agricultural land were affected. Two thirds of all rivers in Chongqing and 275
reservoir dried up. Two thirds of all the districts, a total of 7.95 million people, 7.35 million cattle faced water shortage. 92 incidences of
forest fires devoured 80 million
mu forestation in August. The increase in usage of
air-conditioning placed great strain on electricity supply. During the worst period, there was a shortage in electricity supply of 1.2 million kilowatt. To ensure electricity supply to residential areas, the government rationed supply to industrial areas. Direct economic loss in Chongqing Municipal alone was estimated to be 6.375 billion yuan, among which 5.128 billion from the
agricultural sector.
There is still no conclusive evidence showing any correlations of the drought with the building of
Three Gorges Dam.
See also
- Drinking water
- Flood
- Chinese State Flood Control and Drought Relief Headquarters
- Transvasement
- United Nations Convention to Combat Desertification
References
