Scientists investigate continent-wide 'moisture conveyor belt' behind extreme monsoon rains
Weather scientists have long known that typhoons even hundreds of kilometers away from the Philippines can interact with the southwest monsoon, resulting in multiday heavy rains. But the exact dynamics of this relationship remained largely unknown until recently.
Scientists are investigating a continent-wide moisture conveyor belt responsible for extreme monsoon rains in the Philippines. Weather experts have long known that distant typhoons can interact with the southwest monsoon, causing heavy rainfall. However, the precise dynamics of this relationship were unclear until recently. A new study led by the Ateneo de Manila University VORTEX Research Lab, Manila Observatory, PAGASA, and Tokyo Metropolitan University, published in Atmospheric Research, sheds light on this complex phenomenon and may improve monsoon rain forecasts.
Every year, the southwest monsoon brings rain to western parts of the Philippines, offering relief after hot months. But it can also lead to devastating flooding from relentless downpours. Researchers analyzed over 40 years of extreme Habagat (southwest monsoon) events and found that the heaviest rains result from a combination of atmospheric conditions across thousands of kilometers, not a single weather event.
They identified a recurring pattern: a strengthened Habagat, a tropical cyclone northeast of the Philippines, and favorable atmospheric conditions allowing moisture to flow toward the country. This combination forms the moisture conveyor belt (MCB), transporting water vapor from the Indian Ocean across Southeast Asia to the Philippines.
When these conditions align, they often lead to prolonged periods of intense rainfall. The study reveals that the setup for severe rainfall events takes several days to develop, with the Habagat strengthening over the northern Indian Ocean to establish the MCB. The frequent appearance of this pattern in many extreme cases suggests that the country's most severe southwest monsoon events follow a common pattern rather than occurring randomly.
While existing weather forecasts capture many of these large-scale patterns, the research paves the way for improving predictions of high-impact southwest monsoon events.
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