Pusan National University Study Finds Pollution Shifts Rainfall from Land to Sea in Southeast Asia

Air pollution is dramatically reshaping tropical rainfall patterns. In a new study, scientists found that increasing aerosol concentrations over the Maritime Continent strengthens oceanic rainfall while suppressing and delaying land rain peaks to midnight. This newly identified shift, revealed through high-resolution modeling and satellite data, has major implications for forecasting and climate prediction in Southeast Asia.

PUSAN, South Korea, Oct. 16, 2025 /PRNewswire/ -- Tiny airborne particles known as aerosols, from biomass burning, urban pollution, and industrial emissions, can dramatically alter rainfall, cloud formation, and atmospheric stability. A new study led by Professor Kyong-Hwan Seo of Pusan National University, Korea, shows that aerosols profoundly reshape precipitation over the Maritime Continent, a region including Indonesia, Malaysia, Singapore, Vietnam, Thailand, the Philippines, and surrounding seas, where millions rely on predictable rainfall for water, food, and flood protection.

Published online in npj Climate and Atmospheric Science on September 25, 2025, the study combined a 2-km-resolution atmospheric model with NASA TRMM satellite data and MERRA-2 reanalysis to simulate how varying aerosol levels influence convection and precipitation. The team analyzed a 2011 Madden-Julian Oscillation event and tested other phases and years, finding that high aerosols consistently increased rainfall over the ocean while suppressing it over land.

"As aerosol concentrations rise, the precipitation pattern shifts from a land-enhanced to an ocean-dominant one," said Seo.

In high-aerosol simulations, oceanic rainfall intensified by up to 50%, while land precipitation declined, producing a markedly higher sea-to-land rainfall ratio—a novel discovery confirmed by both model simulations and satellite observations. The mechanism behind this shift is primarily radiative. Aerosols cool the land surface more strongly than the ocean, stabilizing the lower atmosphere over islands while leaving the sea relatively unstable. This difference enhances low-level convergence and convection at sea, drawing moisture away from land.

Seo explained, "Aerosols act like a brake on daytime heating over land, but the ocean hardly feels that brake." High aerosol levels also delay the peak of the diurnal precipitation cycle over land from late afternoon to around midnight, a counterintuitive pattern linked to reduced daytime heating and nighttime buildup of moist static energy.

"We're seeing a delay from the usual late-afternoon storms to a midnight peak," noted Seo.

Some observed high-aerosol events exhibit similar behavior, now revealed in detail through combined modeling and satellite data.

These findings carry important practical applications. In densely populated and flood-prone regions such as Jakarta or Manila, understanding aerosol-driven shifts toward more oceanic rainfall can improve disaster management, irrigation planning, and urban flood preparedness. Short-term forecasts may become more accurate during haze or pollution episodes, helping authorities allocate resources and mitigate risks to infrastructure and transportation. Incorporating these aerosol effects into climate and weather models may also improve predictions of the Madden–Julian Oscillation (MJO), monsoons, and extreme tropical rainfall events, which influence seasonal weather patterns far beyond Southeast Asia. Over the longer term, this research could transform tropical climate forecasting. The study suggests smoother MJO propagation across the Maritime Continent by revealing how aerosols weaken land-based convection—potentially enabling more reliable seasonal rainfall predictions. These insights could support water resource management, food security, and energy planning for millions of people. On a global scale, integrating aerosol impacts into climate models could refine projections of precipitation changes amid rising emissions, helping communities reduce vulnerability to floods and droughts and adapt to climate-driven water challenges in tropical regions.

Reference
Title of original paper: Aerosol effects on Maritime Continent precipitation: Oceanic intensification and land diurnal cycle delay
Journal: npj Climate and Atmospheric Science
DOI: 10.1038/s41612-025-01215-5

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