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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. It can have a substantial impact on the ecosystem and agriculture of the affected region. Although droughts can persist for several years, even a short, intense drought can cause significant damage ^[1] and harm the local economy^[2].

Contents

Implications

Causes

Consequences

Stages of drought

Drought mitigation strategies

See also

References

Implications

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. Recurring or long-term drought can bring about desertification. Recurring droughts in the Horn of Africa have created grave ecological catastrophes, prompting massive food shortages, still recurring. To the north-west of the Horn, the Darfur conflict in neighboring Sudan, also affecting Chad, was fueled by decades of drought; combination of drought, desertification and overpopulation are among the causes of the Darfur conflict, because the Arab Baggara nomads searching for water have to take their livestock further south, to land mainly occupied by non-Arab farming peoples.^[3]
According to a UN climate report, the Himalayan glaciers that are the sources of Asia's biggest rivers - Ganges, Indus, Brahmaputra, Yangtze, Mekong, Salween and Yellow - could disappear by 2035 as temperatures rise.^[4] Approximately 2.4 billion people live in the drainage basin of the Himalayan rivers.^[5] India, China, Pakistan, Bangladesh, Nepal and Myanmar could experience floods followed by droughts in coming decades. Drought in India affecting the Ganges is of particular concern, as it provides drinking water and agricultural irrigation for more than 500 million people.^[6][7][8] Paradoxically, some proposed short-term solutions to global warming also carry with them increased chances of drought.http://environment.newscientist.com/article/dn12397-sunshade-for-global-warming-could-cause-drought.html ''Sunshade' for global warming could cause drought'' 02 August 2007 New Scientist, Catherine Brahic
In 2005, parts of the Amazon basin experienced the worst drought in 100 years.^[9][10] A 23 July 2006 article reported Woods Hole Research Center results showing that the forest in its present form could survive only three years of drought.^[11][12] Scientists at the Brazilian National Institute of Amazonian Research argue in the article that this drought response, coupled with the effects of deforestation on regional climate, are pushing the rainforest towards a "tipping point" where it would irreversibly start to die. It concludes that the rainforest is on the brink of being turned into savanna or desert, with catastrophic consequences for the world's climate. According to the WWF, the combination of climate change and deforestation increases the drying effect of dead trees that fuels forests fires.^[13]

Causes

Generally, rainfall is related to the amount of water vapour in the atmosphere, combined with the upward forcing of the air mass containing that water vapour. If either of these are reduced, the result is drought.
Factors include:

★ Above average prevalence of high pressure systems

★ Winds carrying continental, rather than oceanic air masses (ie. reduced water content)

★ El Nino (and other oceanic temperature cycles)

★ Deforestation

★ some speculate that global warming will have a substantial impact on agriculture ^[14] throughout the world, and especially in developing nations^[15].

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. ^[16]

★ Shortages of water for industrial users. ^[17][18]

★ Desertification

★ Dust storms, when drought hits an area suffering from desertification and erosion

★ 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.

★ Reduced electricity production due to insufficient available coolant
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

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 ^[19]:
#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 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.
#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 ^[20]. Similar circumstances also place their largest lake, Balkhash, at risk of completely drying out ^[21].

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. ^[22] Careful monitoring of moisture levels can also help predict increased risk for wildfires, using such metrics as the Keetch-Byram Drought Index ^[16] or Palmer 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).

★ Cloud seeding - an artificial technique to induce rainfall. ^[24]

See also

★ Climate change and agriculture

★ Drought in Australia

★ Droughts and famines in Russia and USSR

★ United Nations Convention to Combat Desertification

★ Water crisis

References

1. http://www.bom.gov.au/climate/drought/livedrought.shtml
2. Australian Drought and Climate Change, retrieved on June 7th 2007.
3. Looking to water to find peace in Darfur
4. Vanishing Himalayan Glaciers Threaten a Billion
5. Big melt threatens millions, says UN
6. Ganges, Indus may not survive: climatologists
7. Glaciers melting at alarming speed
8. Himalaya glaciers melt unnoticed
9. Environmental News Service - Amazon Drought Worst in 100 Years
10. Drought Threatens Amazon Basin - Extreme conditions felt for second year running
11. ''Amazon rainforest 'could become a desert' '', The Independent, July 23, 2006. Retrieved September 28, 2006.
12. ''Dying Forest: One year to save the Amazon'', The Independent, July 23, 2006. Retrieved September 28, 2006.
13. ''Climate change a threat to Amazon rainforest, warns WWF'', World Wide Fund for Nature, March 22, 2006. Retrieved September 28, 2006.
14. http://www.economics.noaa.gov/library/documents/benefits_of_weather_and_climate_forecasts/drought-climate_change-implications_for_west.doc NOAA DROUGHT AND CLIMATE CHANGE: IMPLICATIONS FOR THE WEST Dec 2002
15. http://usinfo.state.gov/af/Archive/2005/Oct/26-779234.html Nigerian Scholar Links Drought, Climate Change to Conflict in Africa Oct, 2005
16. http://txforestservice.tamu.edu/shared/article.asp?DocumentID=406&mc=fire Texas Forest Service description of the Keetch-Byram Drought Index (KBDI) from 12/27/2002
17. http://www.sfgate.com/cgi-bin/article.cgi?file=/c/a/2005/03/06/MNGE2BL7161.DTL Parched village sues to shut tap at Coke March 6, 2005
18. http://www.greenpeace.org/international/news/sweden-nuclear-closure-040806 Greenpeace reports on a Swedish drought and its potential impact on their nuclear power industry. 04 August 2006
19. http://www.nws.noaa.gov/om/brochures/climate/Drought.pdf NOAA factsheet, retrieved April 100th 2007
20. http://news.bbc.co.uk/2/hi/asia-pacific/6538219.stm BBC article on the World Bank loan to save the Aral Sea
21. http://news.bbc.co.uk/2/hi/asia-pacific/3397077.stm BBC article from 2004 concerning the risk of Kazakhstan losing the lake
22. http://news.bbc.co.uk/2/hi/programmes/from_our_own_correspondent/6530453.stm BBC's From Our Own Correspondent on khat water usage
23. http://txforestservice.tamu.edu/shared/article.asp?DocumentID=406&mc=fire Texas Forest Service description of the Keetch-Byram Drought Index (KBDI) from 12/27/2002
24. http://www.chinadaily.com.cn/english/doc/2004-07/24/content_351196.htm