Pollution is changing the way and where it rains in Southeast Asia, according to a new study. It turns out that air pollution may be doing more than just harming our health, it could also be changing the pattern of rainfall in the region. The study found that small particles in the air, which are released from burning forests, city pollution, and factories, are causing rainfall to move away from land and towards the sea.

The research, led by Professor Kyong-Hwan Seo from Pusan National University in South Korea, examined the Maritime Continent. This area includes countries like Indonesia, Malaysia, Singapore, Vietnam, Thailand, and the Philippines, along with the surrounding seas. Rainfall in this region plays a crucial role; it supports agriculture, provides drinking water, and helps prevent droughts and floods.

The findings were published in the journal npj Climate and Atmospheric Science. The study used advanced weather models and satellite data from NASA to understand how different levels of pollution particles, known as aerosols, influence rainfall and cloud formation.

Studying Weather Events

The researchers analyzed a significant weather event in 2011 known as the Madden-Julian Oscillation (MJO), and they also studied similar patterns in other years. They discovered a clear pattern: when aerosol levels were high, more rain fell over the ocean, and less fell on land.

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

During these high-pollution periods, rainfall over the ocean increased by up to 50%, while the land experienced drier conditions. This shift in rainfall was confirmed by both computer simulations and actual satellite data.

The reason for this change lies in how aerosols affect temperatures. These particles cool the land more than the sea, making the air over land more stable and less likely to rise and create clouds. In contrast, the air over the sea remains more unstable, which encourages the formation of rain clouds. Interestingly, the timing of rainfall also changes.

Pollution Shifts Southeast Asia Rainfall

Normally, tropical land areas receive rain in the late afternoon. However, with high levels of aerosols, the peak rainfall occurs closer to midnight. This change happens because the land doesn't heat up as much during the day, and moisture builds up more slowly.

This finding has important practical implications. Cities like Jakarta and Manila, which are densely populated and prone to flooding, could use this knowledge to better prepare for extreme weather events. It could help in managing water supplies, planning for floods, and organizing emergency responses during periods of high pollution.

In the long term, including the effects of aerosols in weather and climate models could improve the accuracy of forecasts for tropical weather systems like the MJO and monsoons. Better predictions would help countries in the region plan for changing weather conditions, protect crops, manage energy use, and improve water security.

Globally, understanding how pollution affects rainfall could help scientists predict how climate change might influence rain patterns in the tropics, something that millions of people rely on for their daily lives.

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