Air pollution is changing the way rain falls over one of the most densely populated and climatically active regions on Earth.
A new study led by researchers at Pusan National University in South Korea has found that rising concentrations of aerosols, including microscopic particles released from biomass burning, urban pollution, and industrial activity, are altering rainfall patterns across Southeast Asia.
Published in npj Climate and Atmospheric Science on September 25, 2025, the research reveals that as aerosol concentrations increase, rainfall strengthens over the ocean while weakening and delaying over land. The discovery offers new insights into how pollution alters tropical precipitation systems and may help improve weather forecasting for millions who rely on predictable monsoon patterns.
Lead author Professor Kyong-Hwan Seo, Director of the Institute for Future Earth at Pusan National University, stated that the findings indicate a fundamental rebalancing of tropical convection.
“As aerosol concentrations rise, the precipitation pattern shifts from a land-enhanced to an ocean-dominant one,” he said.
High-resolution modelling uncovers a shifting rainfall dynamic
The team combined a 2-kilometre-resolution atmospheric model with NASA TRMM satellite observations and MERRA-2 reanalysis datasets to simulate the effect of aerosols on rainfall and cloud dynamics. Using a 2011 Madden–Julian Oscillation (MJO) event as a reference, they tested multiple cases and years, consistently finding stronger ocean rainfall and weaker land rainfall during high aerosol episodes.
Seo explained that the shift is driven by the way aerosols modify the balance of heating between land and sea. Aerosols scatter and absorb sunlight, cooling the land surface more rapidly than the ocean. The cooled land surface stabilises the lower atmosphere, suppressing convection and cloud formation, while the relatively warmer ocean remains unstable and continues to generate strong updrafts.
“Aerosols act like a brake on daytime heating over land, but the ocean hardly feels that brake,” Seo said. This difference enhances moisture convergence at sea, drawing humid air away from the islands and towards the ocean, which amplifies offshore rainfall.
From afternoon storms to midnight rain: a delayed land rainfall cycle
The modelling results also revealed a delay in the diurnal rainfall cycle over land. Under typical conditions, thunderstorms over Southeast Asian islands develop in the late afternoon, driven by intense solar heating. When aerosol levels are high, however, land surfaces absorb less heat during the day, reducing convective lift.
As a result, rainfall peaks several hours later, often around midnight, as stored heat and moisture finally trigger instability. “We’re seeing a delay from the usual late-afternoon storms to a midnight peak,” Seo noted.
Satellite data confirmed that this delayed pattern occurs during high-pollution episodes, supporting the model’s conclusions. The finding represents a significant advance in understanding how pollution affects the timing and magnitude of tropical rainfall.
Radiative forcing and aerosol–cloud interactions
At the centre of the discovery lies the concept of radiative forcing, where aerosols alter the distribution of energy in the atmosphere. Over land, their cooling effect reduces vertical mixing and convective cloud growth. Over the ocean, the same particles can enhance low-level convergence by maintaining relative instability.
The study also found that high aerosol conditions increase the sea-to-land rainfall ratio by up to 50 per cent. This means a larger proportion of total rainfall occurs over the ocean rather than over land. Such a shift has far-reaching implications for water availability, agricultural timing, and flood risks across island nations.
Aerosol–cloud interactions further amplify these effects. As particles act as cloud condensation nuclei, they influence the size, lifetime, and precipitation efficiency of droplets. These microphysical processes can strengthen or suppress storms depending on humidity and aerosol concentration, making them key variables for next-generation climate models.
Implications for Southeast Asia’s climate and water management
The Maritime Continent, which encompasses Indonesia, Malaysia, Singapore, Vietnam, Thailand, and the Philippines, is highly sensitive to changes in rainfall distribution. Millions rely on consistent precipitation for agriculture, hydropower, and freshwater supply.
The Maritime Continent refers to the collection of tropical islands and surrounding seas that make up much of Southeast Asia, including Indonesia, Malaysia, Singapore, the Philippines, and parts of Vietnam and Thailand. Scientists use the term to describe this region as a single, interconnected land–ocean system that plays a major role in driving global rainfall and atmospheric circulation.
Seo said that understanding the effects of aerosols on rainfall is crucial for improving hazard forecasting and disaster preparedness.
“Regions such as Jakarta and Manila are especially vulnerable,” he said. “Recognising how pollution shifts rainfall offshore and delays land storms can help improve flood management and early warning systems.”
The research suggests that incorporating aerosol feedbacks into climate and weather models could lead to better short-term forecasts during haze or high-pollution episodes. This improvement would be valuable for city planners, agricultural agencies, and emergency management authorities who must anticipate rainfall variability under changing air quality conditions.
Broader significance for monsoons and global climate prediction
Beyond its regional focus, the study offers new insights into the global water cycle. Aerosol-driven cooling of land surfaces may influence the behaviour of larger atmospheric systems such as the Madden–Julian Oscillation and monsoon circulation.
The research suggests that under high aerosol conditions, the MJO may propagate more smoothly across the Maritime Continent due to reduced land-based convection. This finding could improve seasonal rainfall prediction not only in Southeast Asia but also in regions influenced by tropical oscillations, such as northern Australia.
Over longer timescales, integrating aerosol dynamics into global models could refine projections of precipitation changes under continued industrial emissions. As climate variability intensifies, understanding how air pollution interacts with convection and cloud formation will be essential for maintaining water security and reducing vulnerability to floods and droughts.