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Drought
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 (meteorology)|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[Living With Drought] and harm the local economy[Australian Drought and Climate Change, retrieved on June 7th 2007.] According to the UN, an area of fertile soil the size of Ukraine is lost every year because of drought, deforestation and climate instability.[2008: The year of global food crisis]
Implications
Drought is a normal, recurring feature of the climate in most parts of the world. 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 1984 - 1985 famine in Ethiopia|food shortages, 2006 Horn of Africa food crisis|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.[Himalayas|Himalayan glaciers that are the sources of Asia's biggest rivers - Ganges, Indus, Brahmaputra, Yangtze, Mekong, Salween and Yellow River|Yellow - could disappear by 2035 as temperatures rise.][Vanishing Himalayan Glaciers Threaten a Billion] Approximately 2.4 billion people live in the drainage basin of the Himalayan rivers.[Big melt threatens millions, says UN] 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.[Ganges, Indus may not survive: climatologists][Glaciers melting at alarming speed][Himalaya glaciers melt unnoticed]
The west coast of North America, which gets much of its water from glaciers in mountain ranges such as the Rocky Mountains and Sierra Nevada (U.S.)|Sierra Nevada, also would be affected.[Glaciers Are Melting Faster Than Expected, UN Reports][Water shortage worst in decades, official says, Los Angeles Times]
In 2005, parts of the Amazon basin experienced the worst drought in 100 years.[Environmental News Service - Amazon Drought Worst in 100 Years][Drought Threatens Amazon Basin - Extreme conditions felt for second year running] 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.[''Amazon rainforest 'could become a desert' '', The Independent, July 23, 2006. Retrieved September 28, 2006.][''Dying Forest: One year to save the Amazon'', The Independent, July 23, 2006. Retrieved September 28, 2006.] 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 World Wide Fund for Nature|WWF, the combination of climate change and deforestation increases the drying effect of dead trees that fuels forest fires.[''Climate change a threat to Amazon rainforest, warns WWF'', World Wide Fund for Nature, March 22, 2006. Retrieved September 28, 2006.] Paradoxically, some proposed solar shade|short-term solutions Mitigation of global warming|to global warming also carry with them increased chances of drought.[''Sunshade' for global warming could cause drought'' 02 August 2007 New Scientist, Catherine Brahic]
By far the largest part of Australia is Deserts of Australia|desert or semi-arid lands commonly known as the outback. A 2005 study by Australian and American researchers investigated the desertification of the interior, and suggested that one explanation was related to human settlers who arrived about 50,000 years ago. Regular burning by these settlers could have prevented monsoons from reaching interior Australia.[Sensitivity of the Australian Monsoon to insolation and vegetation: Implications for human impact on continental moisture balance, Geological Society of America] In June 2008 it became known that an expert panel had warned of long term, maybe irreversible, severe ecological damage for the whole Murray-Darling basin if it does not receive sufficient water by October.[Australian rivers 'face disaster', BBC News] Australia could experience more severe droughts and they could become more frequent in the future, a government-commissioned report said on July 6, 2008.[Australia faces worse, more frequent droughts: study, Reuters] The Australian of the year 2007, environmentalist Tim Flannery, predicted that unless it made drastic changes, Perth, Western Australia|Perth in Western Australia could become the world’s first ghost town|ghost metropolis, an abandoned city with no more water to sustain its population.[Metropolis strives to meet its thirst, BBC News]
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 a drought. Factors include:
- Above average prevalence of high pressure systems;
- Winds carrying continental, rather than oceanic air masses (ie. reduced water content);
- Ridges of high pressure areas form with behaviors which prevent or restrict the developing of thunderstorm activity or rainfall over one certain region;
- El Nino, La Nina (and other oceanic and atmospheric temperature cycles) and global warming;
- Deforestation and erosion adversly impacting the ability of the land to capture water; [Kenya: Deforestation exacerbates droughts, floods]
- Climate change has a Climate change and agriculture|substantial impact on agriculture[NOAA DROUGHT AND CLIMATE CHANGE: IMPLICATIONS FOR THE WEST December 2002] throughout the world, and especially in developing nations.[Record rise in wheat price prompts UN official to warn that surge in food prices may trigger social unrest in developing countries][Fuel costs, drought influence price increase][http://usinfo.state.gov/af/Archive/2005/Oct/26-779234.html Nigerian Scholar Links Drought, Climate Change to Conflict Africa Oct, 2005]
Consequences
Periods of drought can have significant environmental, agricultural, health, economic and social consequences. Examples include:
- Death of livestock.
- Reduced crop yields.
- Wildfires, such as Australian bushfires, are more common during times of drought.[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]
- Shortages of water for industry|industrial users.[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][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. 4 August 2006]
- 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.
- Substandard or highly limited crop growth or yield productions.
- Mass migration, resulting in internally displaced person|internal displacement and international refugees.
- War over natural resources, including water and food.
- Reduced electricity generation|electricity production due to insufficient available coolant for power stations[U.S. drought may dry up coolant water, close plants - The China Post] and reduced water flow through hydroelectric energy|hydroelectric dams.[http://news.google.com/news/url?sa=t&ct=:ePkh8BM9E-LUYs1LLUjMMWCD21QOtylJiBVokwELpl1GAqd333uhtWuCxaSTZ-4pTDef-ouNNSc_OTHnFxtzUWoyAB_dF94/1-0&fp=483aaabf2810f7de&ei=GLU6SIjcHo2uygSA9fHSAQ&url=http%3A//www.chron.com/disp/story.mpl/ap/fn/5777087.html&cid=1212570023&usg=AFrqEzdBxA44kkxEwUXsQd8weUTm_1ujtw]
- Snakes have been known to emerge and snakebites become more common.[http://news.bbc.co.uk/2/hi/asia-pacific/6282075.stm Australians Face Snake Invasion. ][http://scriptures.lds.org/en/ether/9 Ancient peoples of the Americas describe increase in snake encounters due to drought in the Mormon book of Scripture called The Book of Mormon ]
- Creates windblown dust bowls which erodes the landscape, damages Terrestrial ecoregion|terrestrial and aquatic wildlife habitat
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:[http://www.nws.noaa.gov/om/brochures/climate/Drought.pdf NOAA factsheet, retrieved April 100th 2007]
- Meteorology|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.
- Agriculture|Agricultural droughts are droughts that affect crop production or the ecology of the Range (biology)|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.
- Hydrology|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.[http://news.bbc.co.uk/2/hi/asia-pacific/6538219.stm BBC article on the World Bank loan to save the Aral Sea] Similar circumstances also place their largest lake, Lake Balkhash|Balkhash, at risk of completely drying out.[http://news.bbc.co.uk/2/hi/asia-pacific/3397077.stm BBC article from 2004 concerning the risk of Kazakhstan losing the lake]
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.[http://news.bbc.co.uk/2/hi/programmes/from_our_own_correspondent/6530453.stm BBC's From Our Own Correspondent on khat water usage] 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-dependent 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.[Cloud seeding helps alleviate drought]
See also
- Maya collapse
- Climate change
- Drought in Australia
- Droughts and famines in Russia and USSR
- Drought in the United States
- Food security
- United Nations Convention to Combat Desertification
- Water crisis
- Dust Bowl
- Sahel drought
- Collapse (book)|''Collapse: How Societies Choose to Fail or Succeed'', a 2005 book by Jared Diamond
References
External links
- Water scarcity from FAO Water (Food and Agriculture Organization of the United Nations)
Category:Basic meteorological concepts and phenomena
Category:Climatology
Category:Droughts
Category:Hydrology
Category:Weather hazards
simple:Drought
zh-yue:乾旱
Related Images- Dry earth in the Sonora desert, Mexico.
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