Aerosols intensify oceanic rains and delay land storms until midnight, altering the climate balance of Southeast Asia, causing rainfall displacement.
Atmospheric pollution is drastically altering tropical rain patterns. In a new study, a team of scientists discovered that the increase in aerosol concentrations in the Maritime Continent intensifies oceanic precipitation while suppressing and delaying peak terrestrial rainfall until midnight.
This recently identified change, revealed through high-resolution models and satellite data, has significant implications for forecasting and climate prediction in Southeast Asia.
Tiny airborne particles, known as aerosols (from biomass burning, urban pollution, and industrial emissions), can dramatically alter precipitation, cloud formation, and atmospheric stability.
A new study led by Professor Kyong-Hwan Seo, from the National University of Pusan (Korea), shows that aerosols modify and displace rains in the Maritime Continent. This region includes Indonesia, Malaysia, Singapore, Vietnam, Thailand, the Philippines, and the surrounding seas, where millions of people depend 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’s TRMM satellite data and MERRA-2 reanalysis data. The goal was to simulate how aerosol level variations influence convection and precipitation.
The team analyzed a 2011 Madden-Julian Oscillation event, as well as other phases and years, discovering that high aerosol concentrations consistently increased precipitation over the ocean while suppressing it over land.
“As aerosol concentrations increase, the precipitation pattern shifts from land dominance to ocean dominance,” said Seo.
In simulations with high aerosol levels, oceanic precipitation intensified by up to 50%, while terrestrial precipitation decreased.
This produced a significantly higher land-sea rainfall ratio, a novel finding confirmed by both model simulations and satellite observations.
The mechanism behind this change is mainly radiative. Aerosols cool the land surface more intensely than the ocean, stabilizing the lower atmosphere over the islands, while the sea remains relatively unstable. This difference enhances convergence and convection at low levels in the sea, drawing moisture away from the land.
Seo explained: “Aerosols act as a brake on daytime warming on land, but the ocean barely feels that brake.”
High aerosol levels also delay the peak of diurnal precipitation cycles over land, shifting it from late afternoon to around midnight. This is a counterintuitive pattern linked to reduced daytime warming and the nocturnal accumulation of humid static energy.
“We are seeing a delay between the usual afternoon storms and a peak at midnight,” noted Seo.
Some observed high aerosol concentration events exhibit similar behavior, now detailed through the combination of models and satellite data.
These findings have important practical applications. In densely populated and flood-prone regions like Jakarta or Manila, understanding aerosol-induced changes towards increased oceanic precipitation can enhance disaster management, irrigation planning, and urban flood preparedness.
Short-term forecasts can be more accurate during fog or pollution episodes, helping authorities allocate resources and mitigate risks to infrastructure and transportation. Incorporating these aerosol effects into climate and meteorological models can also improve predictions of the Madden-Julian Oscillation (MJO), monsoons, and extreme tropical rain events, which influence seasonal weather patterns well beyond Southeast Asia.
In the long term, this research could transform tropical climate prediction. The study suggests a smoother propagation of the MJO in the Maritime Continent by revealing how aerosols weaken terrestrial convection, potentially allowing more reliable seasonal precipitation predictions.
This knowledge 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 rainfall displacement with changes in precipitation due to increased emissions.
This would help communities reduce vulnerability to floods and droughts and adapt to water challenges posed by climate in tropical regions.
