Drought could hit world's populous areas: study

WASHINGTON Tue Oct 19, 2010 1:29pm EDT

1 of 5. Handout image of a map showing the drought conditions between 2000 and 2009 for a study by National Center for Atmospheric Research (NCAR) scientist Aiguo Dai, released October 19, 2010.

Credit: Reuters/University Corporation for Atmospheric Research/Handout

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WASHINGTON (Reuters) - Some of the world's most populous areas -- southern Europe, northern Africa, the western U.S. and much of Latin America -- could face severe, even unprecedented drought by 2100, researchers said Tuesday.

Increasing drought has long been forecast as a consequence of climate change, but a new study from the U.S. National Center for Atmospheric Research projects serious impact by the 2030s. Impacts by century's end could go beyond anything in the historical record, the study suggests.

To get an idea of how severe the drought might get, scientists use a measure called the Palmer Drought Severity Index, or PDSI. A positive score is wet, a negative score is dry and a score of zero is neither overly wet nor dry.

As an example, the most severe drought in recent history, in the Sahel region of western Africa in the 1970s, had a PDSI of -3 or -4.

By contrast, the new study indicates some areas with high populations could see drought in the -15 or -20 range by the end of the century.

"Historical PDSI for the last 60 years show a drying trend over southern Europe but nothing like those values at the end of this century," study author Aiguo Dai said in answer to e-mailed questions. "Decadal mean values of PDSI have not reached -15 to -20 levels in the past in any records over the world."

A GENERALLY DRIER WORLD

Areas likely to experience significant drying include:

-- the western two-thirds of the United States;

-- much of Latin America, especially large parts of Mexico and Brazil;

-- regions bordering the Mediterranean Sea;

-- large parts of southwest Asia;

-- southeast Asia, including China and neighboring countries, and

-- most of Africa and Australia.

While Earth is expected to get dryer overall, some areas will see a lowering of the drought risk. These include:

-- much of northern Europe;

-- Russia;

-- Canada;

-- Alaska, and

-- some areas of the Southern Hemisphere.

That doesn't necessarily mean that agriculture will migrate from the drought areas to these places in the high latitudes, Dai wrote.

"The high-latitude land areas will experience large changes in terms of warmer temperatures and more precipitation, and thus may indeed become more habitable than today," he wrote. "However, limited sunshine, short growing season, and very cold nighttime temperature will still prevent farming over most of these high-latitude regions."

The study's findings are based on computer models and the best current predictions of climate-warming greenhouse gas emissions. This could change depending on actual greenhouse emissions in the future as well as natural climate cycles such as El Nino, the center said in a statement.

More information and graphics on the study can be seen here .

(Editing by Paul Simao)

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