On May 13, 2025, the Philippine Atmospheric, Geophysical and Astronomical Services Administration (PAGASA) issued a scorching forecast: 33 areas across the country are expected to experience dangerous levels of heat index, with temperatures in some locations projected to feel like 45 to 46°C.
Topping the list is Cavite City, with an anticipated heat index of 46°C—the highest across the country for the day. Pasay City and Quezon City, both in Metro Manila, are also on high alert, with heat indices forecast at 44°C and 42°C, respectively.
But why do urban centers like Cavite and Metro Manila consistently feel hotter than their rural counterparts?
The Urban Heat Island Effect
The answer lies in a phenomenon known as the Urban Heat Island (UHI) effect—a well-documented occurrence where cities experience significantly higher temperatures than surrounding rural areas. This is primarily due to dense infrastructure, limited greenery, and human activity that collectively trap heat during the day and slowly release it at night, keeping temperatures elevated round-the-clock.
Materials commonly used in urban environments—asphalt roads, concrete buildings, and metal roofs—absorb and retain heat more efficiently than natural surfaces like soil, grass, or trees. The lack of vegetation means less shade and less evapotranspiration, which otherwise helps cool the air.
In cities like Cavite and Metro Manila, high population density and heavy traffic also contribute to localized heating. Air conditioners, vehicles, and industrial processes emit waste heat, further amplifying the already hot environment.
Health at Risk
PAGASA classifies heat index values between 42°C and 51°C as “dangerous”, with increased risk of heat cramps and heat exhaustion. Prolonged exposure could lead to heatstroke, a potentially fatal condition.
Children, the elderly, and outdoor workers are particularly vulnerable, especially in urban areas where shaded rest spaces and hydration access may be limited.
How Can Cities Cool Down?
To combat the Urban Heat Island effect, urban planners and local governments can implement strategies such as:
- Increasing green spaces: Planting more trees, building parks, and encouraging rooftop gardens help cool the air naturally.
- Using reflective or green roofing materials: These reduce heat absorption by buildings.
- Expanding public awareness: Encouraging behavior changes such as avoiding outdoor activities during peak heat hours and staying hydrated.
- Developing heat action plans: Preparedness can save lives, especially during periods of extreme heat.
Looking Ahead
As climate change continues to intensify global temperatures, cities in the Philippines are likely to see more frequent and severe heat waves. The heat index warnings from PAGASA are not just daily weather updates—they are a call to action.
