Drought in the United States is similar to that of other portions of the globe. Below normal precipitation leads to drought, which is caused by an above average persistence of high pressure over the drought area. Changes in the track of extratropical cyclones, which can occur during climate cycles such as the El Niño-Southern Oscillation, or ENSO, as well as the North Atlantic Oscillation, Pacific Decadal Oscillation, and Atlantic Multidecadal Oscillation, modulates which areas would be more prone to drought and when drought develops. Warming climates are expected to increase drought frequency due to increased evaporation. In dry areas, removing grass cover and going with a more natural vegetation for the area can reduce the impact of drought, since a significant amount of fresh water is used to keep lawns green. Droughts are periodic, alternating with floods over a series of years. The worst droughts in the history of the United States occurred during the 1930s and 1950s, periods of time known as Dust Bowl years.
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Generally, rainfall is related to the amount of water vapour in the Earth's atmosphere, combined with the upward forcing of the air mass containing that water vapor.[1][2][3][4][5][6] If either moisture, lift, or atmospheric instability are reduced, rain will be more scant which in time will lead to drought. This can be triggered by an above average prevalence of high pressure systems, winds carrying continental, rather than oceanic air masses (i.e. reduced water content), and ridges of high pressure areas form with behaviors which prevent or restrict the developing of thunderstorm activity or rainfall over one certain region. Oceanic and atmospheric weather cycles such as ENSO make drought a regular recurring feature of the Americas along the Pacific coast. Droughts can develop anywhere in the United States. El Nino and La Nina alters rainfall patterns in the West and along the Gulf coast.[7][8] The North Atlantic Oscillation, Atlantic Multidecadal Oscillation (AMO), and Pacific Decadal Oscillation (PDO) are also significantly tied to droughts in the United States. For example, 52 percent of drought timing and location across the United States is explained by the PDO and AMO. When both in their positive phase, the most extensive droughts occur across the United States.[9]
Human activity can directly trigger exacerbating factors such as over farming, excessive irrigation,[10] deforestation, and erosion adversely impact the ability of the land to capture and hold water.[11] While these tend to be relatively isolated in their scope, activities resulting in global climate change are expected to trigger droughts with a substantial impact on agriculture[12] throughout the world, and especially in developing nations.[13][14][15] Although global warming will result in increased world rainfall,[16] warmer temperatures also bring increased evaporation and increased drought frequency.[17] Along with drought in some areas, flooding and erosion will increase in others. Some proposed solutions to global warming that focus on more active techniques, solar radiation management through the use of a space sunshade for one, may also carry with them increased chances of drought.[18]
Certain regions within the United States are more susceptible to droughts than others. Droughts can be more damaging than tornadoes, tropical cyclones, winter storms and flooding combined. Unlike a hurricane, tornado or flooding, the onset of droughts happen gradually over a long period of time.
In the Nevada "cash for grass" program, the people are paid to remove grass and put in desert landscaping. Xeriscaping calls for the planting of vegetation which is local in origin and more resistant to drought.
When California suffered a severe drought from 1985 to 1991, a California company, Sun Belt Water Inc. was established for the purpose importing water from Canada in marine transport vessels formerly used for oil transport and converted to water carriers. The idea was commercially viable and Sun Belt Water Inc., was selected by the Goleta Water District to enter a long term contract when the government of British Columbia a province of Canada reversed its existing bulk water export policy. The change in government policy led to a claim by Sun Belt Water Inc. against Canada under the provisions of Chapter 11 of the North American Free Trade Agreement (NAFTA).[19]
The National Integrated Drought Information System (NIDIS) Act was signed into law in 2006 (Public Law 109-430). The Western Governors' Association described the need for NIDIS in a 2004 report, Creating a Drought Early Warning System for the 21st Century: The National Integrated Drought Information System. The NIDIS Act calls for an interagency, multi-partner approach to drought monitoring, forecasting, and early warning, led by the National Oceanic and Atmospheric Administration (NOAA).NIDIS is being developed to consolidate data on drought’s physical, hydrological and socio-economic impacts on an ongoing basis, to develop drought decision support and simulation tools for critical, drought-sensitive areas, and to enable proactive planning by those affected by drought. NIDIS (www.drought.gov) draws on the personnel, experience, and networks of the National Drought Mitigation Center, the NOAA Regional Climate Centers, and the Regional Integrated Sciences and Assessments (RISAs), among others. Federal agencies and departments partnering in NIDIS include the U.S. Army Corps of Engineers, the Bureau of Reclamation, the U.S. Geological Survey, NASA, the U.S. Department of Energy, the U.S. Environmental Protection Agency, the National Science Foundation, and the Natural Resources Conservation Service.
The Dust Bowl or the Dirty Thirties was a period of severe dust storms causing major ecological and agricultural damage to American and Canadian prairie lands from 1930 to 1936 (in some areas until 1940). The phenomenon was caused by severe drought coupled with decades of extensive farming without crop rotation, fallow fields, cover crops or other techniques to prevent erosion.[20] Deep plowing of the virgin topsoil of the Great Plains had displaced the natural grasses that normally kept the soil in place and trapped moisture even during periods of drought and high winds.
During the drought of the 1930s, without natural anchors to keep the soil in place, it dried, turned to dust, and blew away eastward and southward in large dark clouds. At times the clouds blackened the sky reaching all the way to East Coast cities such as New York and Washington, D.C. Much of the soil ended up deposited in the Atlantic Ocean, carried by prevailing winds which were in part created by the dry and bare soil conditions itself. These immense dust storms—given names such as "Black Blizzards" and "Black Rollers"—often reduced visibility to a few feet (around a meter). The Dust Bowl affected 100,000,000 acres (400,000 km2), centered on the panhandles of Texas and Oklahoma, and adjacent parts of New Mexico, Colorado, and Kansas.[21]
Millions of acres of farmland became useless, and hundreds of thousands of people were forced to leave their homes; many of these families (often known as "Okies", since so many of them [though not all of them] came from Oklahoma) traveled to California and other states, where they found economic conditions little better than those they had left. Owning no land, many traveled from farm to farm picking fruit and other crops at starvation wages. Author John Steinbeck later wrote The Grapes of Wrath, which won the Pulitzer Prize, and Of Mice and Men about such people.
Other severe drought years in the United States happened through the 1950s. These droughts began in the Southwestern United States, New Mexico and Texas during 1950 and 1951; the drought was widespread through the Central Plains, Midwest and certain Rocky Mountain States, particularly between the years 1953 and 1957, and by 1956 parts of central Nebraska reached a drought index of -7, three points below the extreme drought index.[22] From 1950 to 1957, Texas experienced the most severe drought in recorded history. By the time the drought ended, 244 of Texas’ 254 counties had been declared federal disaster areas.[23]
The Northeastern United States were hit with devastating drought which lasted almost four to five years in the 1960s. The drought affected multiple regional cities from Virginia into Pennsylvania, New Jersey and New York; the drought also affected certain Midwest States.
Short term droughts hit particular spots of the United States during 1976 and 1977, which foretold the drought events that would affect many portions of the USA during the 1980s.
Droughts also affected the Northeast US, Corn Belt and Midwest States during 1980 and 1983. The 1983 Midwestern States Drought was associated with very dry conditions, severe heat and substandard crop growth which affected prices and caused hardship for farmers.[24] Multiple disaster declarations went out in Indiana and neighboring states because of the 1983 drought.[25] Readings of 100 °F (38 °C) or higher became prevalent in 1983 during these dry spells across the Midwest, Ohio Valley Regions and Great Lakes. Kentucky declared the 1983 drought their second worst in the 20th century; the drought forced many trees and shrubs into dormancy and created water shortages in many towns.[26] The associating heat waves killed between 500-700 people in the United States. Similar spells during 1980 caused between 4000 to 12000 deaths in the United States along with $24 billion in damage 1980 USD.
A severe drought struck the Southeast from 1985 through 1987. It began in 1985 from the Carolinas west-southwest into Alabama, when annual rainfall was reduced by 5 to 35 percent below what was normal. Light precipitation continued into the spring of 1986, with Atlanta, Georgia recording their driest first six months on record. High amounts of precipitation during the winter of 1987 ended the drought.[27]
Another significant drought in the United States occurred during 1988 and 1989. Following a milder drought in the Southeastern United States and California the year before, this drought spread from the Mid-Atlantic, Southeast, Midwest, Northern Great Plains and Western United States. This drought was widespread, unusually intense and accompanied by heat waves which killed around 4800 to 17000 people across the United States and also killed livestock across the United States. One particular reason that the Drought of 1988 became very damaging was farmers might have farmed on land which was marginally arable. Another reason was pumping groundwater near the depletion mark. The Drought of 1988 destroyed crops almost nationwide, residents' lawns went brown and water restrictions were declared many cities. The Yellowstone National Park fell victim to wildfires that burned many trees and created exceptional destruction in the area. This drought was very catastrophic for multiple reasons; it continued across the Upper Midwest States and North Plains States during 1989, not officially ending until 1990.[28]
The conditions continued into 1989 and 1990, although the drought had ended in some states thanks to normal rainfalls returning to some portions of the United States.[29] Dry conditions, however, increased again during 1989, affecting Iowa, Missouri, eastern Nebraska, Kansas and certain portions of Colorado.[30] The drought also affected Canada in certain divisions. The Drought of 1988 became the worst drought since the Dust Bowl 50 years before in the United States; 2008 estimates put damages from the drought somewhere between $80 billion and almost $120 billion in damage (2008 USD). The Drought of 1988 was so devastating that in later years it was compared against Hurricane Andrew in 1992 and against Hurricane Katrina;[31][32] in addition, it would be the costliest of the three events: Hurricane Katrina comes second with $81 billion (2005 United States Dollars), Hurricane Andrew coming in third. The Drought of 1988 qualifies being the costliest natural disaster in the history of the United States.
During 1993 the Southeastern United States experienced high temperatures and conditions of drought for extended periods. The heatwaves associated caused the deaths of seventeen people and overall damage from the Southeastern State Drought of 1993 was somewhere between $1 billion and $3 billion in damage (1993 United States Dollars).[33]
Similar drought conditions hit the Northeast United States during 1999 - the Northeast, including Kentucky, New York, New Jersey, Pennsylvania and Maryland were pummeled by extensive heat waves which killed almost 700 people across the Northeastern US and unusually dry conditions caused billions of dollars in destruction during 1999.[34] This unusually damaging drought was reminiscent of the Northeast United States Drought of the 1960s considering it affected similar states within the Northeast United States and New England.
The Midwest and Rocky Mountains became victims during 2002; the regions fell victim under exceptional drought which was accompanied by dry conditions, wildfires and hot temperatures over the Western US and Midwestern State areas.[35][36] The US Drought of 2002 turned a "normal" fire season to very dangerous, treacherous and violent. Denver was forced to impose mandatory limits regarding water for the first time in twenty one years. The Drought of 2002 was very bad in Colorado and certain other States in the West.[37][38] Also, the Quad Cities had around eight inches (203 mm) below average during 2002 (normal precipitation is 38.06 inches (967 mm) every year); during 2002, 30.00 inches were recorded.
The US Drought of 2002 was so reminiscent of the 1988 Drought and compared against the Droughts of the 1930s, the 1983 Drought and the Dry Spells of the 1950s. The drought also affected Saskatchewan, Manitoba and Alberta in Canada.[39]
Although the Western United States and Southwestern US are most likely to be hit, droughts can also happen over the Upper Midwestern States, the Central Great Plains, Southeast United States, the Middle Atlantic, the Great Lakes Region, the Ohio River Valley, Northeastern United States and even New England. Droughts vary in severity and have potential for causing elevated to exceptional damage wherever they focus their area toward.
There were extensive droughts through the first decade of the 21st century all over the Southeastern United States, continuing as far westward as Texas. The Southeastern United States were affected by heavy droughts extending from the Carolinas toward Mississippi and even into Tennessee and Kentucky. Droughts affecting Florida were so severe lakes were actually drying out. Wildfires, forest fires and brush fires were very prevalent in association with the first decade of the 21st century Drought in the Southeastern United States.
Missouri, Arkansas, (portions of) Louisiana, Tennessee, southeast Iowa and northern Illinois were hit with severe droughts and heat during 2005.[40][41] The conditions caused $1 billion in overall damage, there were no deaths attributed to the drought and associated heat spells. The Quad Cities themselves received only 17.88 inches (454 mm) of precipitation during 2005.
In 2008 and 2009, much of south and south-central Texas were in a state of exceptional drought.[42]
From 2008-2011 the state of California endured through a 3 year drought. First declared by Governor Arnold Schwarzenegger in 2008, as he tried to win voter support for an $11 billion bond to build new water projects, like new dams and peripheral canals. Voters will decide on this measure in 2012. California officially ended its drought in March 2011, when Governor Jerry Brown deemed the "drought emergency" over.[43]