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.
Fields outside Benambra, Victoria suffering from drought conditions
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 (or above 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.
Periods of drought can have significant environmental,
economic and social consequences. The most common consequences are:
- Ground drag and Desertification.
- Loss of agricultural production
- Famine due to lack of water for irrigation
- Social unrest
- Migration or relocation of those impacted
- War for water and foods.
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
See also: Aqueduct and trasvasement.
18th and 19th centuries, Cape Verde
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 died from drought, starvation
1921-22, Soviet Union
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.
1936, Sichuan Province, China
This was the worst drought in the modern history of
the area. 34 million farmers were displaced and 5 million people starved.
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. These migrants became the "Okies" whose experience was recorded
in literature and song of the period.
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
Much of Australia has typically low rainfall and drought
is defined as rainfall in the lowest ten percent of records. In the past
five to ten years there have been major rainfall deficiencies across large
parts of Australia. Many regions have placed heavy restrictions on water
usage and some towns have been forced to import water.
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 (112.1° F), 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 (13,000 km²) of agricultural
land were affected. Two thirds of all rivers in Chongqing and 275 reservoirs
dried up. Two thirds of all the districts, a total of 7.95 million people
and 7.35 million cattle faced water shortage. 92 incidences of forest fires
devoured 80 million mu (53,000 km²) of 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 was from the agricultural sector.
There is still no evidence showing any correlations
of the drought with the building of Three Gorges Dam.