What caused Metro Manila's worst flood in years?

John Gabriel Agcaoili, ABS-CBN News

Posted at Nov 13 2020 02:48 AM | Updated as of Nov 13 2020 05:50 AM

What caused Metro Manila's worst flood in years? 1
Barangay Barangka, located near the Marikina River, is inundated in floodwaters after typhoon Ulysses swept through Luzon on Thursday, November 12, 2020. Fernando G. Sepe Jr., ABS-CBN News​

MANILA (UPDATED)- Typhoon Ulysses's heavy rains in Metro Manila on Thursday triggered memories of Tropical Storm Ondoy which struck the region with heavy rainfall and severe flooding more than a decade ago and left at least 464 dead.

Analysts have compared the two tropical cyclones, with some saying Ulysses was stronger in terms of rainfall due to the height of floodwater late Wednesday until Thursday morning in Metro Manila and nearby suburbs.

But an official of state weather bureau PAGASA said Ondoy was still more intense and that Ulysses' downpour was not the lone cause of the severe flooding in the capital region.

According to Dr. Esperanza Cayanan, deputy administrator of PAGASA's research and development division, Ondoy brought more rains in 2009.

"Kung gagamitin po natin 'yung observation sa Science Garden natin sa Quezon City, ay 153 mm lang po sa loob ng 24 hours 'yung ating na-observe doon (Ulysses), compared kay Ondoy na more than 400 plus," Cayanan told ABS-CBN's TeleRadyo.

(If we're going to use the observation in our science garden in Quezon City, we only observed 153 mm of rainfall within 24 hours from Ulysses, compared to Ondoy which had more than 400 mm.)

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"So, ang ibig sabihin po, 'yung pumatak na ulan (mula kay Ulysses) sa Metro Manila, particularly sa Quezon City, ay hindi ganoon kalakas. So, saan nanggaling ngayon 'yung maraming tubig na nagpabaha dito po sa Pasig River, sa Metro Manila?" she said.

(So, this means Ulysses' downpour in Metro Manila, particularly in Quezon City, was not that heavy. So where did the water come from that resulted in the flooding of Pasig River, of Metro Manila?)

This meant that Ulysses' rainfall in nearby mountainous areas flowed towards Metro Manila's rivers and creeks, filling them up until they overflowed.

"'Yun po 'yung ating obserbasyon nung nangyari kay Ulysses," Cayanan said.

(That's our observation on what happened with Ulysses.)

Ulysses, the 21st tropical cyclone to hit the country this year and the 8th for the past two months, forced tens of thousands of residents across the country to evacuate, with some scrambling onto rooftops to await rescue amid severe flooding.

Millions of households in Metro Manila, Rizal, Bicol Region and other areas also experienced power outage due to Ulysses.

The typhoon slammed into areas still reeling from Rolly, this year's most powerful typhoon, which killed at least 25 people and destroyed thousands of homes in early November.

Ulysses is expected to leave the country's area of responsibility on Friday, PAGASA said in its 11 p.m. advisory.

President Rodrigo Duterte has ordered government agencies to hasten relief efforts. pledging shelter, relief goods, financial aid and counseling to those who were affected.