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Drought

2007 Schools Wikipedia Selection. Related subjects: Climate and the Weather

   Fields outside Benambra, Victoria suffering from drought conditions
   Fields outside Benambra, Victoria suffering from drought conditions

   A drought is an extended period of months or years when a region notes
   a deficiency in its water supply. Generally, this occurs when a region
   receives consistently below average precipitation. However, it can also
   be worsened by man. It can have a substantial impact on the ecosystem
   and agriculture of the affected region. Although droughts can be
   long-lived, even a short, intense drought can cause significant damage
   .

   Man-made erosion can play a role, as it did in the North American Dust
   Bowl in the 1930s, as can general climate change. Many speculate that
   global warming will have a substantial impact on agriculture throughout
   the world, and especially in developing nations. For most regions,
   drought is a normal, recurrent feature of the climate, and having
   adequate drought mitigation strategies in place can greatly reduce the
   impact. Regardless of the cause, recurring drought can also bring about
   desertification. Recurring droughts in the Horn of Africa have created
   grave ecological catastrophes, prompting massive food shortages, still
   recurring.

Consequences

   Periods of drought can have significant environmental, economic and
   social consequences. The most common consequences include:
     * Death of livestock.
     * Reduced crop yields.
     * Wildfires, such as Australian bushfires, are more common during
       times of drought.
     * Shortages of water for industrial users.
     * Desertification
     * Dust storms
     * Malnutrition, dehydration and related diseases.
     * Famine due to lack of water for irrigation.
     * Social unrest.
     * Mass migration, resulting in internal displacement and
       international refugees.
     * War over natural resources, including water and food.

   The effect varies according to vulnerability. For example, subsistence
   farmers are more likely to migrate during drought because they do not
   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.

Stages of drought

   Ship stranded by the retreat of the Aral Sea
   Ship stranded by the retreat of the Aral Sea

   As a drought persists, the conditions surrounding it gradually worsen
   and its impact on the local population gradually increases. Droughts go
   through three stages before their ultimate cessation :
    1. 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.
    2. Agricultural droughts are droughts that affect crop production or
       the ecology of the range. This condition can also arise
       independently from any change in precipitation levels when soil
       conditions and erosion triggered by poorly planned agricultural
       endeavors cause a shortfall in water available to the crops.
       However, in a traditional drought, it is caused by an extended
       period of below average precipitation.
    3. Hydrological drought is brought about when the water reserves
       available in sources such as aquifers, lakes and reservoirs falls
       below the statistical average. Like an agricultural drought, this
       can be triggered by more than just a loss of rainfall. For
       instance, Kazakhstan was recently awarded a large amount of money
       by the World Bank to restore water that had been diverted to other
       nations from the Aral Sea under Soviet rule . Similar circumstances
       also place their largest lake, Balkhash, at risk of completely
       drying out .

Drought mitigation strategies

     * Desalination of sea water for irrigation or consumption.
     * Drought monitoring - Continuous observation of rainfall levels and
       comparisons with current usage levels can help prevent man-made
       drought. For instance, analysis of water usage in Yemen has
       revealed that their water table (underground water level) is put at
       grave risk by over-use to fertilize their Khat crop. Careful
       monitoring of moisture levels can also help predict increased risk
       for wildfires, using such metrics as the Keetch-Byram Drought Index
     * Land use - Carefully planned crop rotation can help to minimize
       erosion and allow farmers to plant less water-dependant crops in
       drier years.
     * Rainwater harvesting - Collection and storage of rainwater from
       roofs or other suitable catchments.
     * Recycled water - Former wastewater (sewage) that has been treated
       and purified for reuse.
     * Transvasement - Building canals or redirecting rivers as massive
       attempts at irrigation in drought-prone areas.
     * Water restrictions - Water use may be regulated (particularly
       outdoors). This may involve regulating the use of sprinklers, hoses
       or buckets on outdoor plants, the washing of motor vehicles or
       other outdoor hard surfaces (including roofs and paths), topping up
       of swimming pools, and also the fitting of water conservation
       devices inside the home (including shower heads, taps and dual
       flush toilets).

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   with only minor checks and changes (see www.wikipedia.org for details
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