Many parts of the world are expected to suffer more frequent, more widespread, and more severe droughts as a result of climate change. Drought will likely be one of the most significant impacts of climate change on ecosystems and human society, but adaptation can lessen its effects.

A drought is a period when the water supply of a given area is insufficient for the needs of humans or of ecosystems, usually resulting from below-normal precipitation. If defined simply as a precipitation deficit, such an event is called a meteorological drought. If a drought depletes soil moisture and harms crops, it is an agricultural drought. Eventually, lack of precipitation will diminish water levels in lakes, rivers, and aquifers; this is a hydrological drought. If a drought affects human well-being, it can be called a socioeconomic drought. These categories overlap, and there are many other ways to define droughts based on their causes or effects.

Precipitation patterns result from large-scale atmospheric and oceanic processes, which in turn are affected by solar forcing, atmospheric composition, land-surface characteristics, and other factors. Scientific understanding of these processes is imperfect but improving; for example, in the 1980's, it was discovered that a cyclical variation in Pacific sea surface temperature called the El Nino-Southern Oscillation (ENSO) has a profound effect on rainfall around the world. Paleoclimate records show that short- and long-term rainfall fluctuations are common and predate human history, though the causes are often unclear.

Another important cause of drought is above average temperatures, which increase evaporation and hasten loss of soil moisture. Warm temperatures can also cause precipitation to fall as rain instead of snow, causing it to run off rather than being stored and gradually released. Human land use, such as deforestation or poor soil management, can contribute to drought. Droughts may have multiple causes; for example, the 1930's Dust Bowl event in the U.S. Great Plains was a result of both meteorological drought and erosion-prone farming techniques.

Drought has both direct and indirect effects. The direct effects most relevant to human well-being include reduced water supply (both in quantity and quality); crop failure, especially of rain-fed crops; loss of livestock; soil degradation, such as through dust storms and desertification; death of forests, often resulting in wildfires; and electricity shortages (if hydropower is used). These effects, in turn, can have profound consequences for human society, including mortality (due to starvation, thirst, fire, or dust); large-scale migration, often to urban centers; economic depression and entrenchment of poverty; and, under very adverse conditions, violent conflict. Ecosystems can usually survive and may even benefit from periods of drought; however, an especially severe drought may cause biodiversity loss and long-term disruption of ecosystem processes.

There is general agreement that climate change is likely to worsen droughts worldwide, but the location, timing, and magnitude of these effects are highly uncertain. Averaged globally, climate change will increase precipitation by speeding ocean evaporation. However, rising temperatures will affect oceanic and atmospheric circulation patterns, changing the global distribution of rainfall. Some regions will become wetter; others, drier. Even in regions where total precipitation does not decrease, drought risk may increase as a result of faster land-surface evaporation, loss of water stored in snow and ice, and greater variability of precipitation events (causing not only droughts but also floods).

Climate models generally agree that several regions of the world are likely to suffer from decreased precipitation and increased drought risk under future climate. These regions include the Mediterranean (southern Europe and northern Africa); southern Africa, especially its southwest corner; the southwestern United States; parts of Central America; and southern Australia. Semiarid and arid regions will probably be hardest hit by drought, with subsistence farmers in developing countries being especially vulnerable. In addition, climate change may cause water shortages wherever populations depend upon glaciers or snowmelt for their water supply, such as the Andes in South America, the Himalayas in central Asia, and the Sierra in California.

Close monitoring of atmospheric conditions can reveal an impending drought before its agricultural or socioeconomic symptoms become severe, allowing protective measures to be taken. This is the basis of drought early-warning systems, for which there are several regional and global networks. Once a drought has begun, relief efforts may be necessary. Such efforts may include allocation of water to communities and farms, cash payments to farmers, and relocation assistance. However, the availability of relief can ultimately increase vulnerability to drought by encouraging inappropriate settlement and farming practices.

Although drought cannot be prevented, its effects can be minimized through adaptation. Examples of drought adaptation include selecting drought-tolerant crops; improving agricultural soil management; reducing the size of livestock herds; controlling fuel loads in forests; building dams and reservoirs; and encouraging water conservation. A society can insulate itself against drought (or any hazard) by reducing poverty, diversifying its economy, and building strong social institutions.

Humans have always needed to cope with drought; it has been a cause of hardship, conflict, and migration throughout recorded history. Mega-droughts may have led to the disappearance of some civilizations, such as the Maya. More than 10 million people are thought to have been killed by drought during the twentieth century. Climate change will likely not only increase the incidence of drought but add other stresses to human society as well.

Drought is a natural phenomenon, and a given drought cannot be attributed definitively to climate change. Furthermore, there is much uncertainty about when and where climate change will increase drought incidence. This does not, however, imply that adaptation efforts should be delayed. Many drought-adaptation actions will have benefits in the present as well as the future.

References:

1)         Boken, Vijendra K., Arthur P. Cracknell, and Ronald L. Heathcote, eds. Monitoring and Predicting Agricultural Drought: A Global Study. New York: Oxford University Press, 2005.

2)         Botterill, Linda C., and Melanie Fisher, eds. Beyond Drought: People, Policy, and Perspectives. Collingwood, Vic.: Commonwealth Scientific and Industrial Research Organisation, 2003.

3)         Cooley, Heather. "Floods and Droughts." Chapter 4 in The World's Water, 2006-2007: The Biennial Report on Freshwater Resources, edited by Peter Gleick. Washington, D.C.: Island Press, 2006.

4)         Intergovernmental Panel on Climate Change. Climate Change, 2007--The Physical Science Basis: Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change. Edited by Susan Solomon et al. New York: Cambridge University Press, 2007.

5)         Kallis, Giorgos. "Drought." Annual Review of Environment and Resources 33 (2008): 85-118.

6)         Trenberth, K. E., J. T. Overpeck, and S. Solomon. "Exploring Drought and Its Implications for the Future." Eos 85, no. 3 (January 20, 2004): 27.

Free term papers are not written to satisfy your specific instructions. You can use our professional writing services to buy a custom written research paper, term paper, or essay on Global Warming at affordable price. CustomTermPapers is the best solution for those who seek help in writing term papers, essays, and research papers related to Global Warming and other relevant topics.