Why are some areas 'colder' despite extreme heat? PAGASA explains

Dry weather, exacerbated by the El Niño phenomenon, has left many Filipinos drenched in sweat.

But for Silvestre Aben, who grew up in La Trinidad, Benguet, it remains cool up north despite the extreme heat in most parts of the country. 

"For this time, mga 26 degrees Celsius. Kung sa hapon, bababa pa ng mga 24°C to 25°C. Talagang ganito ang temperature dito sa Benguet," he told GMA News Online. 

(For this time, it’s 26 degrees Celsius. In the afternoon, it reaches between 24°C and 25°C. This is how the temperature is here in Benguet.) 

"Walang pinagbago. Talagang ganun ang weather dito sa Benguet. Kapag aakyat ka pa sa north, mas malamig doon," Aben added.

(Nothing really changed. That’s how the weather is in Benguet. If you go up north, it’s colder there.) 

State weather bureau PAGASA has recorded dangerous levels of heat index across the country since March. 

Heat index is the measure of the temperature that a person feels in contrast to the actual air temperature. It is computed by factoring in the humidity and the air temperature, according to the state weather bureau. 

On April 28, the heat index in Iba, Zambales, rose to an extremely dangerous level of 53°C — the highest in the country so far this year. 

Around 25 areas also reported dangerous levels of heat indexes of up to 45°C on May 9. 

Topography

But despite the extreme heat, some areas remained relatively cooler, reporting lower heat indexes. These include Baguio City, La Trinidad, Benguet, and Tanay, Rizal. 

In the last five days, La Trinidad reported heat indexes of 25°C (May 9), 27°C (May 8), 29°C (May 7), 26°C (May 6), and 27°C (May 5). 

Meanwhile, Baguio monitored heat indexes of 25°C (May 9), 27°C (May 8), and 28°C (May 5 to May 7).

The municipality of Tanay experienced heat indexes of 34°C (May 9), 32°C (May 8), 33°C (May 7), 32°C (May 6), and 33°C (May 5). 

John Manalo, a PAGASA weather specialist, explained that an area's terrain has an impact on the heat index.

“Maraming factors na nagpapataas o nagpapababa ng heat index measurements na nao-obserbahan natin. Isa po dito ay 'yung elevation or 'yung topography,” said Manalo.

(There are many factors affecting heat index measurements. One of the factors is elevation, or the area’s topography.)

“'Yung mga lugar na nasa highly-elevated o 'yung matataas gaya ng Baguio…relatively, mas malamig o lower 'yung temperature..as compared sa mga low-lying areas, halimbawa, Metro Manila,” he added. 

(Highly elevated areas such as Baguio City experience lower temperatures compared to low-lying areas like Metro Manila.)

“May role din ang distance from the nearest body of water…Kung sa Manila Bay, the more na mas malapit sa body of water, mas may tendency na mas mataas ang relative humidity dahil sa moisture content na dala ng mga body of water,” Manalo said. 

(An area’s distance to the nearest body of water also plays a role. Coastal areas such as Manila Bay have higher relative humidity due to the moisture content of the body of water.)

Warmer Baguio

Although Baguio is known for its cold climate, Sam Silverio noticed that today’s heat is different from the previous years. 

“Hindi ganun kainit compared sa Manila, pero mainit pala compared to usual Baguio weather,” she told GMA News Online. 

(It’s not that hot compared to Manila, but this is hotter compared to the usual Baguio weather.)

“Gumigising na ako madalas basa ng pawis eh (I now often wake up sweating).''

Rachel Santos said that the heat in Tanay is still bearable compared to Metro Manila, but she also noticed that it is different from the past.

“As compared sa mga nagdaang summer season, iba talaga yung init ngayon kahit saan,” she told GMA News Online. 

(As compared to the previous summer seasons, it is very hot anywhere else.)

PAGASA said the infrastructure and establishments in an area can also influence the heat index. Dubbed the “urban heat island effect,'' cities record warmer indexes than rural areas due to the buildings and establishments around them.

“Ang urban areas ay relatively mas warmer compared sa nearby rural areas niya dahil sa differences sa structures and materials na nakikita natin sa urban areas,” said Manalo.

(Urban areas are relatively warmer than rural areas because of the differences in structures and materials.)

“Ang main difference nila ay heat capacity…Mas maraming buildings, mas may tendency na ma-hold nila yung warm air. Unlike sa rural na magdi-dissipate agad ang warm air, sa rural naga-accumulate siya and imbis na mapunta sa upper part ng atmosphere, nagt-transfer pa siya from one building to another o hino-hold pa siya ng asphalt o concrete or metals na meron kadalasan sa urban areas,” he added. 

(The main difference is the heat capacity. Buildings tend to hold warm air, unlike in rural areas where the warm air easily dissipates. The warm air in urban areas accumulates and even transfers from one building to another. The asphalt, concrete, and metal materials in urban areas also hold warm air.)

In Benguet, Aben said that it’s much cooler back in the day when there were still more trees. 

“Nung bata pa kami, malamig na malamig nun. Kasi marami pang kahoy nun, pero ngayon wala na, naubos na ang kahoy,” he said. 

(When we were young, it was very cold then. Because there were still many trees, but there are fewer of them now.) — VBL, GMA Integrated News