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Forecast: global warming may bring giant drought

Oct. 19, 2010
Courtesy of the U.S. National Science Foundation
and World Science staff

Thanks to glob­al warm­ing, the Un­ited States and many oth­er pop­u­lous coun­tries face a grow­ing threat of long, harsh drought in the next 30 years, a new study in­di­cates.

If the pro­jec­tions “come even close to be­ing real­ized, the con­se­quenc­es for so­ci­e­ty world­wide will be enor­mous,” said Aiguo Dai of the U.S. Na­tional Cen­ter for At­mos­pher­ic Re­search in Boul­der, Co­lo., who con­ducted the re­search.

Projected drought con­di­tions at this cen­tury's end, ac­cord­ing to a new study. (Cour­tesy NCAR).
His anal­y­sis con­cludes that glob­al warm­ing will likely cre­ate in­creas­ing dry­ness across much of the globe, pos­sibly reach­ing a scale in some re­gions by the cen­tu­ry’s end rare­ly, if ev­er, seen in mod­ern times.

Us­ing an en­sem­ble of 22 com­put­er cli­mate mod­els and a com­pre­hen­sive in­dex of drought con­di­tions, as well as anal­y­ses of pre­vi­ously pub­lished stud­ies, Dai re­ports that by the 2030s, dry­ness is likely to in­crease sub­stanti­ally across most of the West­ern Hem­i­sphere, along with large parts of Eur­a­sia, Af­ri­ca, and Aus­tral­ia.

In con­trast, higher-latitude re­gions from Alas­ka to Scan­di­na­via are likely to be­come moister, but not enough to bal­ance out the dry­ing else­where, Dai pre­dicts.

Dai cau­tioned that the find­ings are based on the best cur­rent pro­jec­tions of emis­sions of green­house gas­es, which trap heat in the at­mos­phere. What hap­pens will de­pend on many fac­tors, in­clud­ing nat­u­ral cli­mate cy­cles such as El Niño.

The find­ings ap­pear this week as part of a long­er pa­per in the re­search jour­nal Wi­ley In­ter­dis­ci­plin­ary Re­views: Cli­mate Change. The study was sup­ported by the U.S. Na­tional Sci­ence Founda­t­ion.

“This re­search does an ex­cel­lent job of plac­ing fu­ture warm­ing-induced drought in the con­text of the his­tor­i­cal drought record,” said Er­ic DeWeaver, pro­gram di­rec­tor in founda­t­ion’s Di­vi­sion of At­mos­pher­ic and Geo­space Sci­ences. “The work ar­gues credibly that the worst con­se­quenc­es of glob­al warm­ing may come in the form of re­duc­tions in wa­ter re­sources.”

While re­gion­al cli­mate pro­jec­tions are less cer­tain than those for the globe as a whole, Dai’s study in­di­cates that most of the west­ern two-thirds of the Un­ited States will be sig­nif­i­cantly dri­er by the 2030s. Oth­er places predicted to face a sig­nif­i­cant dry­ing threat in­clude much of Lat­in Amer­i­ca, in­clud­ing large sec­tions of Mex­i­co and Bra­zil; re­gions bor­der­ing the Med­i­ter­ra­nean Sea, which could be­come es­pe­cially dry; large swaths of South­west Asia; most of Af­ri­ca and Aus­tral­ia, with par­tic­u­larly arid con­di­tions in re­gions of Af­ri­ca; and South­east Asia, in­clud­ing parts of Chi­na and neigh­bor­ing coun­tries.

The study al­so finds that drought risk can be ex­pected to de­crease this cen­tu­ry across much of North­ern Eu­rope, Rus­sia, Can­a­da, and Alas­ka, as well as some ar­eas in the South­ern Hem­i­sphere. But “the in­creased wet­ness over the north­ern, sparsely pop­u­lated high lat­i­tudes can’t match the dry­ing over the more densely pop­u­lated tem­per­ate and trop­i­cal ar­eas,” Dai said.

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Thanks to global warming, the United States and many other populous countries face a growing threat of long, harsh drought in next 30 years, a new study indicates. If the projections “come even close to being realized, the consequences for society worldwide will be enormous,” said Aiguo Dai of the U.S. National Center for Atmospheric Research, who conducted the research. His analysis concludes that global warming will likely create increasing dryness across much of the globe, possibly reaching a scale in some regions by the century’s end rarely, if ever, seen in modern times. Using an ensemble of 22 computer climate models and a comprehensive index of drought conditions, as well as analyses of previously published studies, Dai reports that by the 2030s, dryness is likely to increase substantially across most of the Western Hemisphere, along with large parts of Eurasia, Africa, and Australia. By later this century, many of the world’s most densely populated regions will be threatened with severe drought. In contrast, higher-latitude regions from Alaska to Scandinavia are likely to become moister, but not enough to balance out the drying elsewhere, Dai predicts. Dai cautioned that the findings are based on the best current projections of emissions of greenhouse gases, which trap heat in the atmosphere. What happens will depend on many factors, including natural climate cycles such as El Niño. The findings appear this week as part of a longer paper in the research journal Wiley Interdisciplinary Reviews: Climate Change. The study was supported by the U.S. National Science Foundation. “This research does an excellent job of placing future warming-induced drought in the context of the historical drought record,” said Eric DeWeaver, program director in foundation’s Division of Atmospheric and Geospace Sciences. “The work argues credibly that the worst consequences of global warming may come in the form of reductions in water resources.” While regional climate projections are less certain than those for the globe as a whole, Dai’s study indicates that most of the western two-thirds of the United States will be significantly drier by the 2030s. “We are facing the possibility of widespread drought in the coming decades, but this has yet to be fully recognized by both the public and the climate change research community,” Dai said. Other countries and continents that could face significant drying include much of Latin America, including large sections of Mexico and Brazil; regions bordering the Mediterranean Sea, which could become especially dry; large swaths of Southwest Asia; most of Africa and Australia, with particularly dry conditions in regions of Africa; and Southeast Asia, including parts of China and neighboring countries. The study also finds that drought risk can be expected to decrease this century across much of Northern Europe, Russia, Canada, and Alaska, as well as some areas in the Southern Hemisphere. But “the increased wetness over the northern, sparsely populated high latitudes can’t match the drying over the more densely populated temperate and tropical areas,” Dai said.