What causes extreme monsoon rains? Scientists explain
MANILA, Philippines — Scientists from the Ateneo de Manila University found that extreme southwest monsoon rains are driven not by a single weather event, but by a combination of atmospheric conditions that come together across thousands of kilometers.
The study spearheaded by the Ateneo de Manila University VORTEX Research Lab and the Manila Observatory, together with the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) and Tokyo Metropolitan University, analyzed 53 cases of extreme southwest monsoon rainfall linked to tropical cyclones between 1981 and 2023.
The experts looked for weather patterns that appeared repeatedly across different cases.
They identified a recurring setup: a strengthened monsoon; a tropical cyclone northeast of the Philippines and other atmospheric conditions that allowed large amounts of moisture to flow toward the country.
The study said the factors form what is known as the “moisture conveyor belt” that transports water vapor from the Indian Ocean across Southeast Asia to the Philippines. When these conditions are in place, they often lead to prolonged periods of intense rainfall.
The researchers found that the buildup to these severe rainfall events takes several days.
The research said as the monsoon strengthens over the northern Indian Ocean, it helps establish the moisture conveyor belt that repeatedly, in many of the cases analyzed, indicates that the country’s most severe southwest monsoon events follow a common pattern rather than occur purely by chance.
The experts said the findings could help scientists better recognize the atmospheric conditions that favor these episodes.
The researchers also found that existing operational weather forecasts capture many of these large-scale patterns, providing a foundation for further improving predictions of high-impact southwest monsoon events.
The research was authored by Alwin Andriel Bathan, Lyndon Mark Olaguera, Faye Abigail Cruz, Jose Ramon Villarin, John Manalo and Jun Matsumoto.
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