Habagat, cyclones bring average 483 mm of rain to Metro Manila in 10 days

MANILA, Philippines — The amount of rain that fell in Metro Manila over the past two weeks underscores the need for better flood infrastructure and a government that can ensure resources intended for flood control translate into protection, a data scientist said.

Dr. Alicor Panao, an associate professor at the University of the Philippines, examined rainfall in Metro Manila from Aug. 5 to 14, when the southwest monsoon, or Habagat, and a series of tropical cyclones brought intense rains to Luzon.

Data from 23 Philippine Atmospheric, Geophysical and Astronomical Services Administration (Pagasa) stations with usable observations showed an average of 483.4 millimeters of cumulative rainfall during the 10-day period.

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That translates to an average daily accumulation of about 48.3 mm, although rainfall varied considerably among the stations.

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Panao, a data scientist for the Inquirer, noted that nearly half of the rainfall recorded during the period fell in just two days, Aug. 9 and 10. On Aug. 9 alone, Pagasa’s Airport station recorded 226.5 mm of rain.

“That is extraordinary rain,” he said.

READ: Luzon gets more than a month’s worth of rain in just 9 days – Pagasa

However, that amount was still below Metro Manila’s historical extreme in 2009, when Tropical Storm Ondoy battered the capital and brought intense rain that set a record of 455 mm in a single day at Pagasa’s Science Garden station, surpassing the previous record of 334 mm in June 1967.

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What makes the current rainfall episode worth noting, Panao said, is the sheer amount of rain accumulated over just 10 days. If 483.4 mm of rain fell evenly over a 1-square-kilometer area, it would amount to about 483.4 million liters of water over the period.

Applied uniformly across Metro Manila’s roughly 620 square kilometers, the resulting volume would be equivalent to about 120,000 Olympic-size swimming pools, or roughly 193 pools for every square kilometer.

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READ: Habagat rains disrupt classes for 8.4M learners across 8 regions

From Aug. 5 to 14, Sitio Wawa recorded 708.0 mm of cumulative rainfall, equivalent to 708 liters of water per square meter. San Mateo-2 recorded 701.0 mm, while La Mesa Dam recorded 645.5 mm over the same period.

As Panao pointed out, “repeated heavy rainfall leaves drainage systems, rivers and watersheds with little time to recover.”

“This makes flood protection more than a question of building more structures,” he said.

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“It is a question of whether public infrastructure is properly designed, built and maintained. This is particularly urgent as investigations continue to uncover alleged ghost, substandard, and overpriced flood-control projects, with criminal cases presumably now underway,” he said. /dm