Ocean Temperatures Set Up Drought Conditions

Associated Press Writer

January 30, 2003, 2:00 PM EST

WASHINGTON -- Unusual temperatures in the Indian and Pacific oceans set up the perfect conditions for drought stretching nearly around the world in 1998-2002, climate researchers report.

The four-year 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 Friday's issue of the journal Science.

During that four-year period drought plagued much of the United States, southern Europe and southwest Asia. The researchers concluded that all three were the result of the same unusual ocean conditions.

Cold sea surface temperatures in the eastern tropical Pacific and warm sea surface temperatures in the western tropical Pacific and Indian Oceans worked together to cause the widespread drying, said Hoerling, based at the Climate Diagnostics Center in Boulder, Colo.

A warming of the eastern tropical Pacific has since occurred, helping spur storms and rain that have eased the drought in the Eastern states, he noted.

But the 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 which produced the drought that actually occurred. All of the results produced 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 due to global greenhouse warming, the researchers said. That suggests, they added, that if such warming continues there is an increased risk of synchronized drought at mid-latitudes in the future.

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 Nino and La Nina -- have been linked to changes in weather around the world. However, this study added data from the Indian Ocean, not part of most past analyses.