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N.African dust stimulates monsoons

Desert dust from North Africa and the Arabian peninsula stimulates monsoon rains over India, said a study Sunday suggesting that desertification from global warming may boost these seasonal downpours.

Analysis of satellite data showed that dusty conditions in North Africa and West Asia were followed within days by stronger monsoon rains in the subcontinent, according to research published in the journal Nature Geoscience.

"Dust in the air absorbs sunlight west of India, warming the air and strengthening the winds carrying moisture eastward," the US-based Pacific Northwest National Laboratory said in a press release.

"This results in more monsoon rainfall about a week later in India."

Indians have long known that heavy dust brought by strong winds occurs frequently just before monsoon rains, but no scientific link has previously been drawn.

"The study... shows that natural airborne particles can influence rainfall in unexpected ways, with changes in one location rapidly affecting weather thousands of miles away," said the statement.

Commenting on the findings, William Lau of NASA's Earth Science Division said the reported effect could become more pronounced with climate change.

"The expected expansion of desert and arid regions under global warming could enhance dust transport from the deserts of the Middle East and North Africa to the Asian monsoon regions, further enhancing monsoon rainfall," he said.

The researchers stressed that dust was not the only phenomenon to affect monsoons.

Others factors include temperature differences between land and ocean, changes in land use, global warming and local effects of pollution heating or cooling air and affecting clouds.

"The strength of monsoons has been declining for the last 50 years," said study co-author Phil Rasch.

"The dust effect is unlikely to explain the systematic decline, but it may contribute."