Drought conditions tied to ocean temps

Published: Friday, January 31, 2003 at 6:01 a.m.
Last Modified: Thursday, January 30, 2003 at 10:24 p.m.



  • Science:
    www. sciencemag.org

  • WASHINGTON - A band of drought that stretched nearly around the world for four years has been connected to a set of unusual ocean temperatures that set up what researchers called perfect conditions for drought.
    The 1998-2002 drought affected much of the United States as well as southern Europe and southwest Asia.
    And while they can't be certain, National Oceanic and Atmospheric Administration climate scientists Martin Hoerling and Arun Kumar say it may be a harbinger of droughts to come. Their analysis is published in today's issue of the journal Science.
    Hoerling, based at the Climate Diagnostics Center in Boulder, Colo., said the widespread dryness resulted from the combination of cold sea surface temperatures in the eastern tropical Pacific and warm sea surface temperatures in the western tropical Pacific and Indian Oceans.
    Since then, a warming of the eastern tropical Pacific helped spur storms and rain that have eased the drought in the eastern United States, he noted. But dry conditions persist in the west and in parts of Asia, a situation for which he doesn't yet have an explanation.
    The scientists established the link using three different climate models, complex computer programs that use mathematical equations to calculate changes in the weather as warmth, moisture, wind and other conditions change.
    They ran the models 50 times using slightly different starting conditions each time and then adding the actual recorded sea surface conditions. They averaged the results that showed the drought that actually occurred. All of the results showed drier than normal conditions over the drought-plagued areas.
    Could this lead to forecasting droughts in the future? "We certainly hope so," Hoerling said.
    He said he and Kumar, of the Climate Prediction Center in Camp Springs, Md., were surprised at how strong the link was in the model results, indicating the droughts were all caused by the same source.
    "The warmth in the west Pacific during 1998-2002 simply has no precedent in at least the past 150 years," Hoerling said.
    The warming is partly because of global greenhouse warming, the researchers said. That suggests that if such warming continues, there is an increased risk of synchronized drought at mid-latitudes in the future, they added.
    Mathew Barlow of Atmospheric and Environmental Research Inc., in Lexington, Mass., called the paper a "very interesting work that adds information to the dynamics that affect the drought in southwest Asia."
    Barlow, who was not part of the research team, is studying drought in the Afghanistan-Pakistan region, seeking ways to make seasonal forecasts to assist humanitarian efforts there.
    He noted that the drought there was part of a Northern Hemisphere pattern involving the United States and stretching from the Mediterranean to northern India.
    Randall Dole, director of the Climate Diagnostics Center but not a participant in the study, said the study "provides compelling evidence for the crucial role that the tropical oceans played in producing widespread severe and sustained drought over the period 1998-2002."
    Unusual warming and cooling in the Pacific - known as El Nio and La Nia - have been linked to changes in weather around the world by affecting the amount of moisture in the air and changing the upper level winds that can direct weather movement. This study added data from the Indian Ocean, not part of most past analyses.

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