Last August 30, I was browsing my Facebook page when videos of flooding in Quezon City appeared on my wall. Several vehicles were trapped, some floating in chest-deep water. The water must have risen quickly for these vehicles to be placed in a dire situation. Even the Elliptical Circle became an instant river.
The following day, the reason for the deluge was explained. In a single hour, the severe localized thunderstorm in Quezon City poured 121 mm to 141 mm of rain. The onslaught surpassed even the notorious Typhoon Ondoy of 2009, which recorded about 90 mm/hour. The DOST-PAGASA Science Garden Station located in Quezon City recorded 134.2 mm of rainfall from 1:00PM to 4:00PM, which is nearly equivalent to one week’s worth of rainfall based on the monthly normal of 568.5 mm.
The UP-Resilience Institute and NOAH’s Dr. Mahar Lagmay called the Quezon City flooding “worse than torrential- it was extreme.” The city’s drainage system could not simply absorb the enormous volume of water. Many people were caught by surprise and had no sufficient time to react, that’s why many were stranded and several vehicles submerged.
Is this extreme flooding caused by failed flood control projects, poor solid waste management or a rare rainfall occurrence? Probably a combination of all. Perhaps climate change has something to do with it too. Warming affects monsoon behavior, amplifies tropical cyclone impacts, and brings heavier precipitation.
In July this year, PAGASA Administrator Dr. Nathaniel Servando said that climate change is causing global temperatures to rise, a trend that is also reflected in local temperature records. He said average air temperatures in the Philippines have been steadily increasing alongside this global pattern, noting that rising temperatures also cause sea surface temperatures to climb.
Dr. Servando explained that when the temperature of our oceans is high, it produces more water vapor, which fuels tropical cyclones to become more intense. More water vapor means heavier rainfall when there is climate change or global warming. In one of my lectures on climate change, this is the same explanation I gave when asked by a high school student how global warming is influencing typhoons.
There’s a possibility that severe flooding will happen again in the future. The Philippine Climate Change Assessment reports that tropical cyclone‑induced rainfall has increased 16.9% to 19.3% per decade since 2000, reinforcing that extraordinary downpours are more likely now than in the past.
With what happened in Quezon City, engineers and planners might want to rethink their design criteria for drainage systems. They must be designed, or the existing ones redesigned, not for historical averages but for potentially daily deluges stretching beyond past records. The reliance on past climate patterns was made obsolete by nature’s new extremes. That’s part of climate change adaptation.
By the way, PAGASA announced that there’s an increasing probability of short-lived La Niña conditions as early as the September-October-November season until the October-November-December season. La Niña is characterized by an above-average number of tropical cyclone occurrences towards the end of the year and above-normal rainfall conditions in most parts of the country. This means more floods to come.