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3Qs: Back to the dust bowl?

8/1/12

The western and southern United States is cur­rently expe­ri­encing the worst drought since 1988, prompting the U.S. Depart­ment of Agri­cul­ture to declare a fed­eral dis­aster area in 1,300 coun­ties across 29 states. Drought, says civil and envi­ron­mental engi­neering pro­fessor Auroop Gan­guly, has a major impact on food pro­duc­tion and fresh­water secu­rity, in addi­tion to per­sonal safety, which has been impaired by wild­fires sparked by the lack of pre­cip­i­ta­tion. We asked Gan­guly to explain the effects of cli­mate change on drought and its impact on the environment.

The western and southern United States is cur­rently expe­ri­encing the worst drought since 1988. We asked Auroop Gan­guly, a pro­fessor of civil and envi­ron­mental engi­neering, to explain the effects of cli­mate change on drought and its impact on the environment.

Is there evidence to suggest that the U.S. will soon experience a major drought?

Droughts are not easy to define, much less to describe or pre­dict with pre­ci­sion. Large droughts, such as the Dust Bowl of the 1930s in the U.S., how­ever, are unmis­tak­able. Con­di­tions such as reduced pre­cip­i­ta­tion over a rel­a­tively long period of time and con­tin­u­ously increasing tem­per­a­tures, which in turn cause more evap­o­ra­tion, tran­spi­ra­tion and snowmelt, can lead to droughts. The U.S. has had a par­tic­u­larly warm winter this year and an unusu­ally hot summer, dom­i­nated by heat waves across the nation. While cer­tain regions have had normal or more than usual pre­cip­i­ta­tion, other regions have expe­ri­enced deficits. The West and South­west, as well as the Mid­west and Great Plains, have been expe­ri­encing drought con­di­tions and may even be on the verge of major droughts. Increased agri­cul­tural demand and pop­u­la­tion growth or move­ment may exac­er­bate the sit­u­a­tion. It is still too early to say with con­fi­dence, how­ever, that major droughts are in the near future and whether they will rival the Dust Bowl. We are also better pre­pared to deal with droughts in this country than we were in the 1930s.

Will climate change cause more droughts and floods?

An overall warming envi­ron­ment is expected to cause more intense and more fre­quent hydro-meteorological extremes. The pos­si­bility of more severe droughts and floods in dif­ferent regions of the globe is part of what has been called global weirding. These generic state­ments, how­ever, need to be carefully caveated. We are barely begin­ning to under­stand the processes gov­erning heavy rain­fall, and our under­standing of droughts and their trig­gers are rather lim­ited. Land-​​atmosphere and sur­face hydrology processes within the cli­mate change con­text are the pri­mary sources of uncertainty.

Obser­va­tional analyses already point to severe water stress in regions across the globe: mas­sive drying in western and south­western U.S., deser­ti­fi­ca­tion of Spain and Por­tugal, and rapid deple­tion of ground­water in India. Cli­mate models are pointing to future droughts in regions such as the western U.S. with increasing con­fi­dence, but large uncer­tain­ties con­tinue to exist in other regions, such as the Mid­west and Southeast.

Increasing trends in heavy rain­fall and floods have been observed in regions across the globe, and cli­mate models pre­dict con­tinued increase across the land regions of the extra­t­ropics. Pre­dic­tion skills typ­i­cally decrease with higher pre­ci­sion, how­ever, and uncer­tain­ties tend to be larger over the tropics and subtropics.

What are the potential effects of major droughts, and how can we take precautionary measures to limit their damage?

Major droughts can have dev­as­tating con­se­quences across sec­tors ranging from food and fresh­water security to energy pro­duc­tion and ecology. Ulti­mately, human well-​​being is adversely affected, leading to the pos­si­bility of migra­tions and even loss of lives. In a glob­al­ized world, the impacts of regional droughts may be more imme­di­ately felt across the globe. Thus, long-​​lasting and intense droughts in the U.S. Mid­west, which is some­times hailed as the bread­basket of the world, can have severe impli­ca­tions for national and global food secu­rity. In addi­tion, drought con­di­tions are cur­rently preva­lent in many regions across the globe.

Poorer sec­tions of society are usu­ally the least able to adapt and hence most likely to suffer from droughts and other haz­ards, while richer soci­eties may have more to lose in terms of assets. Pre­cau­tionary mea­sures typ­i­cally need to be region and sit­u­a­tion spe­cific. Thus, in the Mid­west, lessons learned from the Dust Bowl era have led to changes in farming and cul­ti­va­tion prac­tices. In cer­tain areas, regional plan­ning and urban­iza­tion may be impor­tant factors.

Mounting evi­dence sug­gests that cur­tailing fossil-​​fuel emis­sions may directly reduce the pos­si­bility of major droughts in the future. Irre­spec­tive of any links with cli­mate change, how­ever, regional droughts will con­tinue to occur, global pop­u­la­tion will increase and lifestyles will con­tinue to grow more demanding. Adap­tive man­age­ment and mit­i­ga­tion at regional scales will, then, be necessary.

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