Why Quezon City was hit the hardest: Five days worth of rain dumped in just one hour
An "extreme" amount of rain on Aug. 30 caused severe flooding across several districts of Quezon City, submerging areas like Barangay South Triangle, Katipunan Avenue, and Commonwealth Avenue.
The QC government said that Districts 1, 3, and 4 bore the brunt of the downpour, with a total of 36 out of 142 barangays affected.
A preliminary analysis by the UP Resilience Institute (UPRI) and the UP NOAH Center described the rainfall as "phenomenal" due to its unprecedented intensity.
Data from PAGASA rain gauges and the city government's IRISEUP program showed that 121 millimeters of rain fell within one hour, surpassing the peak hourly intensity recorded during Typhoon Ondoy in 2009, which had a record of 90 millimeters of rain per hour.
Meanwhile, weather anchor and ABS-CBN News resident meteorologist Ariel Rojas said on X that the Saturday afternoon downpour in the city is equivalent to about five days of rain, dumped in just one hour.
Dr. Mahar Lagmay, executive director of UPRI, echoed this, saying he was stunned by the magnitude of the downpour.
"Grabe terible naman pala ang ulan kaninang hapon sa Quezon City[!] That's a lot of rain delivered in a very short span of time. Most of that 141 mm record in QC was delivered from 2 p.m. to 3 p.m.," he wrote.
"It was worse than torrential rain (30-60 mm/hour). It was extreme (>60 mm/hour). I never thought I would experience such an event," he added.
Peachy de Leon, the spokesperson of the QC Disaster Risk Reduction and Management Office, noted that areas near creeks were flooded.
"Sa waterways po kasi nag-alert level 3 si San Juan River. So 'yung mga dinaanan nitong rivers, 'yun ang talagang tumaas," she told DZBB in a radio interview on Aug. 31, adding that the rainfall was "phenomenal."
Data from PAGASA showed that Quezon City recorded 141 mm of rain over 24 hours, with a peak rate of 121 mm/hour. This means Quezon City experienced more intense rainfall in one hour than many cities receive in an entire day.
According to the QC government, the flash flooding in the areas was also due to the overwhelmed drainage systems, which were unable to handle such volumes of water in a short span of time.
"Hindi kinaya ng drainage system ng lungsod ang napakaraming tubig-ulan sa napakaikling oras kaya nagresulta ito ng malalang pagbaha, maging sa ilang lugar na hindi karaniwang binabaha," it said.
In his analysis of Lagmay's and UPRI's findings, Dr. Tony Leachon, former Special Adviser of the National Task Force COVID-19, highlighted how the flooding was "hyperlocalized" to QC and Nangka, Marikina.
"This anomaly underscores the importance of localized weather monitoring and targeted urban planning," he wrote in a Facebook post. "Urban flooding is increasingly driven by microclimate anomalies—not just typhoons or seasonal monsoons."
Leachon also emphasized that the flooding was caused by rainfall delivered "too fast" for the city's infrastructure to absorb or redirect.
"Infrastructure must be designed not just for total rainfall, but for peak hourly intensity, which is often the tipping point... Static plans must evolve with climate data, urban expansion, and real-time monitoring," he added.
Moving forward, Leachon called for a broader climate resilience agenda for the city, such as real-time rainfall monitoring, infrastructure audits, nature-based solutions, community engagement, and climate-adaptive governance.
At 2:10 p.m. on Saturday, PAGASA issued a thunderstorm advisory for intense to torrential rain showers with lightning and strong winds in Metro Manila and several other areas, which it said would persist within the following two hours.
