Moisture belt triggers strong monsoon rains

A STUDY conducted by the Ateneo de Manila University alongside the Manila Observatory, the Philippine Atmospheric, Geophysical and Astronomical Services Administration, and the Tokyo Metropolitan University revealed that there is a “moisture conveyor belt” that brings extreme monsoon rains in the country.

Using analysis from over four decades of extreme southwest monsoon, the researchers found that extreme rains were driven not by a single weather event but by a combination of atmospheric conditions that come together across thousands of kilometers.

The researchers analyzed 53 cases of extreme monsoon rainfall linked to tropical cyclones between 1981 and 2023, looking for weather patterns that appear repeatedly across different cases.

They found a recurring setup among these events: a tropical cyclone northeast of the Philippines and other atmospheric conditions that allowed large amounts of moisture to flow toward the country.

Once a so-called moisture conveyor belt (MCB) transmits water vapor from the Indian Ocean across Southeast Asia to the Philippines was added to these conditions, there was a prolonged period of intense rainfall.

The study also noted that the buildup to these severe rainfall events takes several days, saying that as the southwest monsoon strengthens over the northern Indian Ocean, it helps establish the MCB that repeatedly, in many of the cases analyzed, indicated that the country’s most severe southwest monsoon events follow a common pattern rather than occur purely by chance.

The findings, according to the researchers, could help scientists better recognize the atmospheric conditions that favor these episodes.