Monsoon likely to get a boost from West Asian dust storm

Dust storms in West Asia and North Africa can increase the Indian summer monsoon rainfall a week later, scientists have found.

Dust in the air absorbs sunlight, warming up the air. This in turn strengthens eastward movement of the Arabian Sea winds carrying moisture, resulting in more rainfall a few days later in India.

“Natural dust and sea salt dominate the aerosol loading. If there is a large dust wave in West Asia and North Africa, it will enhance monsoon rainfall in India within a week,” V Vinoj, lead author of the study from Indian Institute of Technology, Bhubaneswar, told Deccan Herald.

Published in the March 16 issue of “Nature Geoscience”, the study shows that natural aerosol particles (dust) influence rainfall in unexpected ways, with changes in one location rapidly affecting weather thousands of miles away.

While several studies were conducted on the influence of man-made aerosols (soot and carbon) on the weather over the Indian subcontinent, there is barely any research involving natural dust.

India relies heavily on its summer monsoon rains. “The difference between a monsoon flood year or a dry year is about 10 per cent of the average summer rainfall in central India. Variations driven by dust may be strong enough to explain some of that year-to-year variation,” said co-author climate scientist Philip Rasch at Pacific Northwest National Laboratory, Washington.

The researchers used satellite data and sophisticated computer models to establish a clear link between dust storms and rain enhancement.

“The lesson for us is to take the dust factor into account in our numerical weather prediction models particularly while making short-term weather forecast,” said M Rajeevan, a weather scientist associated with the Ministry of Earth Sciences, which is not associated with this research.

“It is an important study and is very consistent on a short time-scale,” said Rajeevan.
One of the drawbacks of the study, however, is that it ignores the long-term consequences of increased dust flow in the atmosphere. If the dust particles stay longer, it blocks the sunlight and cool the sea surface temperature.

“Over longer timescales, this cooling effect may reduce the north–south temperature gradient, suppressing monsoon rainfall over the Indian subcontinent,” said William Lau from Nasa’s Goddard Space Flight Centre, Maryland, who is also not associated with the study.