Data shows that various areas in the Philippines have already been experiencing high heat index levels for the past 10 years

Anna Dayola knows the Philippine heat all too well. 

Her daily three-hour commute is already grueling enough, but as a public school teacher, she also has to walk from one building to another inside the Parañaque National High School (PNHS) campus, leaving her short of breath every time. She sweats more easily, and she’s also prone to migraines, which, she said, the heat can aggravate.

Dayola takes pride in how the PNHS administration accommodates its students whenever it’s especially hot. The school recently scheduled all onsite classes in the morning, so everyone gets home by the time the heat is at its harshest in the afternoon. There is also consideration for students who need to take time off to recover until they’re healthy enough to attend in-person classes again.

But these adjustments can only do so much to alleviate the impact of this year’s excessive heat.

“The academic calendar shift really is no joke, especially for public schools…. Sometimes, there are students who get dizzy spells, or they can’t come to school because they get asthma attacks or migraines. Sometimes, their parents tell them not to go to school if they already think the heat is going to be difficult to bear even before they leave the house,” Dayola said in Filipino.

While it feels like we’ve been experiencing hotter-than-normal days for the past few months, data from the last 10 years analyzed by Rappler showed that 2024’s heat index levels have actually been consistent with heat indices throughout the last decade – proof that Filipinos have long been bearing the brunt of extreme heat and the effects of climate change.

The extreme heat during this year’s dry season has been affecting Filipinos across the country, suspending classes, causing illnesses, and hurting people’s livelihoods and the economy. If global temperatures continue to rise by 2ºC, scientists said repeats of this year’s extreme heat can be expected every two to three years in the Philippines, which may lead to various climate issues down the line.

“It is reasonable to expect that this type of heat will be the norm in the future because of rising global temperatures,” Gerry Bagtasa, professor at the Institute of Environmental Science and Meteorology at the University of the Philippines Diliman, said in an interview with Rappler. 

“There are various problems that we may face later on, like if crops are unable to withstand higher temperatures, food storage can be a problem, or certain diseases become more prevalent due to higher temperatures.”

Heat index: What does it mean?

In the past couple of weeks, news and government reports have often cited the heat index, which refers to what people “perceive or feel as the temperature affecting their body.” It measures both the actual air temperature and relative humidity, which both contribute to the feeling of worsening heat. During the dry season, which Filipinos often call “summer,” hotter days are expected.

PAGASA categorizes heat index levels based on its potential effects on the body:

Rappler looked at PAGASA heat index data from the past 10 years, from 2014 to 2024. The analysis showed that previous dry seasons have also recorded high heat index levels above 52°C, which fall under the “extreme danger” category – similar to PAGASA’s analysis. Filipinos in areas with “extreme danger” heat index levels are likely to suffer from heat stroke if directly exposed to the sun.

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Bagtasa defined heat index as a “measure of comfort” but added that there are other factors that influence how individual bodies perceive heat. These include the clothes we wear, the activities we’re doing, and whether or not we’re directly exposed to the sun.

Some areas are also more prone to excessive heat than others, according to climate experts. Factors that contribute to the heat in a given location include:

• Topography, particularly:
  • Distance from the nearest bodies of water – Coastal areas, such as Dagupan in Pangasinan and Iba in Zambales, see higher heat indices.
  • Elevation – High-elevation areas, such as Baguio, Tanay, and Malaybalay, record lower heat index levels.
• Urbanization
• El Niño
• Overall global warming

Because heat index takes both actual air temperature and relative humidity into consideration, Bagtasa explained that even a change in one of the parameters can lead to a change in the recorded heat index. A rise in relative humidity will make it more difficult for sweat to evaporate, contributing to a “stickier” and more uncomfortable feeling, even if the actual air temperature does not change.

Topography plays a role in how humid certain areas are. For instance, areas situated near bodies of water often record higher heat index levels.

“For example, Dagupan often records the highest heat index levels. Or Iba, Zambales, because Zambales is a coastal region. It’s hot because it’s next to the coast, and the humidity tends to be high. Dagupan is situated near Lingayen Gulf, where moisture from the West Philippine Sea enters,” Bagtasa explained in a mix of Filipino and English.

Dagupan, Pangasinan has consistently recorded high heat index levels during the dry season. Over the past decade, Dagupan recorded “extreme danger” levels of heat indices in seven different years. Heat indices in the area peaked at 53°C in 2017, 54°C in 2019 and 2020, 55°C in 2016 and 2022, 56°C in 2021, and 57°C in 2015. In 2024, Dagupan’s highest heat index was at 51°C, recorded on April 29.

Iba town in Zambales is typically not as hot as Dagupan, but it recorded the country’s highest heat index level in 2024 as of writing, at 53°C last April 28. This marked the first time that Iba’s heat index levels hit the “extreme danger” category over the past decade.

Elevation plays a part in temperatures and heat index levels, too. In an interview with Rappler, John Manalo of PAGASA’s Climatology and Agrometeorology Division explained that elevation and temperature are inversely related, which is why mountainous areas often see lower heat index levels.

“If you’ll notice, in Baguio, they don’t really experience high heat index levels. Of course, it’s because of their elevation, so they’ll experience lower temperatures…. The higher you are, like Malaybalay, or a mountain area, Tanay, the lower your temperatures are,” Manalo said in a mix of Filipino and English.

As opposed to the high heat indices of Dagupan and Iba, the three mountainous areas mentioned by Manalo experience much lower heat index levels. 

Baguio consistently recorded the lowest heat indices across PAGASA stations, just barely grazing the “caution” category. Tanay is slightly warmer, having hit the “danger” category only once in the past decade, in May 2017. Malaybalay also recorded low heat index levels throughout the last 10 years, but has also recorded heat indices in the “danger category” in five different years, including 2024.

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While it’s common for PAGASA stations to record high heat index levels from March to May, Manalo said there are exceptions, as seen in Virac, Catanduanes, which, he said, may continue to see high heat indices until the “ber” ‘months.

What else is causing this year’s excessive heat?

This year’s excessive heat is also caused by the outgoing El Niño, a climate pattern where eastern Pacific waters are warmer. This leads to fewer clouds being formed in the Philippines, which translates to fewer tropical cyclones and higher temperatures in the country. (READ: Is the Philippines prepared for El Niño?)

Bagtasa cited the 2016 El Niño, where parts of the Philippines also suffered from uncomfortable heat similar to that of this year’s. However, Manalo said that El Niño’s impacts on heat indices across the country aren’t consistent. El Niños may differ in magnitude, and other climate patterns can also impact which areas will be affected.

For instance, droughts hit areas in Mindanao in 2016, but it was areas in Luzon that experienced droughts in 2024. From March to June 2016, there were a few instances when Malaybalay in Bukidnon – a typically cooler area – recorded higher heat indices than Iba, Zambales – a coastal area that’s usually more humid.

There’s also the issue of urbanization. Highly urbanized areas largely use materials such as concrete and asphalt, which hold more heat and can lead to higher temperatures.

Scientists recently found that this year’s heatwave in the Philippines would have been impossible without the climate crisis. Earlier in 2024, PAGASA recorded its highest temperature yet in Metro Manila, where air temperature at the Ninoy Aquino International Airport in Pasay hit 38.8°C on April 27. This beat Metro Manila’s all-time record from over a century ago in 1915, when air temperature in the Port Area in Manila hit 38.6ºC.

Experts and activists have warned of worse to come, and have emphasized the need for authorities to prioritize climate resilience.

“Climate change is already staring us in the face. We’ve seen the tremendous impact that record-high temperatures have had on all Filipinos, especially on our most vulnerable sectors. The scenarios…of extreme heat becoming more intense and frequent as the climate crisis worsens are conditions that our current systems would simply not withstand,” Greenpeace Philippines campaigner Khevin Yu said in a statement.

What do we need to do next?

The Philippines remains among the countries most vulnerable to climate change, which leads to extreme weather events and physical and mental health risks. Bleak climate projections have prompted experts and activists to call for urgent climate action.

For instance, teachers and other experts suggested making classrooms more climate-resilient, which may include improving ventilation and installing more drinking fountains.

“Hopefully, we get to address the issue of ventilation, and future buildings will be able to adapt to hot situations. It doesn’t make sense to add more buildings only to end up with poor ventilation. It’s not healthy,” Dayola said.

There are also increasing calls for countries to aggressively pursue just energy transition. During the COP28 conference held in late 2023, over 100 nations agreed to triple renewable energy capacity by 2030, signaling the “beginning of the end” of the fossil fuel era.

Bagtasa brought up the possibility of investing in solar energy to convert the heat into something practical, and governments even considering incentivizing it, just like how the Iloilo City government did earlier this March.

Under the clean energy scenario in the Philippine Energy Plan for 2020-2040, the government aims to reduce greenhouse gas emissions by at least 12%. Business tycoons in the country are also teaming up to invest in a facility for liquefied natural gas, seen as a “transition fuel” between coal and renewable energy sources.

Beyond calling on the Philippine government to “stop delaying the transition to renewable energy,” environment group Greepeace also urged the government to hold fossil fuel companies accountable for their “disproportionate role in historical carbon emissions.”

“[The Philippine government] must scrap its plans for fossil gas expansion, and demand payment from the biggest climate-polluting companies most responsible for the crisis we’re suffering,” Yu said.

Understanding the impacts of extreme heat and climate change will help save Filipinos in the long run, but governments and authorities need to act soon before it’s too late.

In a mix of Filipino and English, Bagtasa said, “I think the imminent future is scary, if this is going to be the norm. I don’t know what will happen. But it is what it is, we just have to adapt.” – Rappler.com