New research finds that heavy pollution in Southeast Asia is suppressing rainfall over land while intensifying it over the ocean.
Cars, factories, and power plants are producing tiny particles, called aerosols, that turn cities hazy. By blocking sunlight, aerosols have a cooling effect, and that effect is more pronounced over land, where pollution is concentrated, than it is over the sea.
“Aerosols act like a brake on daytime heating over land, but the ocean hardly feels that brake,” said Kyong-Hwan Seo of Pusan National University in South Korea, lead author of the new research.
To understand the impact on weather, scientists modeled the effect of aerosols in Southeast Asia, from Thailand to the Philippines, and the surrounding seas. They found that when pollution spikes, rainfall grows up to 50 percent more intense over the ocean. The reason, they believe, is that as warm air rises over the sea, it draws moisture away from the land, yielding heavier downpours.
On land, however, rainfall is more meager and, instead of coming down late in the day, it tends to come down overnight. “We’re seeing a delay from the usual late-afternoon storms to a midnight peak,” said Seo.
Researchers said the findings, published in npj Climate and Atmospheric Science, can help weather forecasters determine when pollution will diminish rainfall, helping officials to better predict floods and better manage the supply of fresh water.
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