Heat index | Inquirer Opinion
Gray Matters

Heat index

Since many of our schools still have classes, science and math classes should find ways to discuss the heat wave we’re going through, one of the worst, maybe even the worst, in years, from identifying signs of dehydration (and emphasizing dehydration can kill), to preventing the dehydration.

It’s not just a matter of absolute temperatures. Weather tracking stations now calculate a heat index, which considers the temperature and humidity. The Philippines suffers from extremes using the two indicators.

Yesterday’s Inquirer had a front-page photograph of a family in the nearly dry Bustos Dam in Bulacan, with a caption reporting the heat indices in the country as ranging from 34 degrees Celsius in Basco, Batanes, to 44 degrees Celsius in Dagupan, Pangasinan, and Catarman, Northern Samar. Metro Manila’s heat indices ranged from 41 to 43 degrees Celsius.


Omnicalculator.com has two online sites where you can calculate your local heat index and dew point index. I have one of those gadgets with readings for both temperature and humidity and plugged in the values, and the result was a sweltering 52 degrees Celsius heat index.


The actual formulas for calculating the heat index are complicated; in Filipino we would say “nakaka-stroke,” enough to cause a stroke. If you love numbers, you’ll find a Wikipedia entry on the heat index with all the formulas. Otherwise, I suggest you just use the omnicalculator.

More importantly, we have to use the heat index to help people plan their lives. Weather reports in print and broadcast media would do well to start using the heat index and what it means. Here’s a simplified summary:


A heat index of 27 to 32 degrees Celsius means fatigue can occur with prolonged exposure and activity, with possible heat cramps. Even young healthy people will feel the impact but can manage easily but with the elderly, the pregnant, and the sick, we should start taking precautions.

When the heat index is between 32 and 41 degrees Celsius, extreme caution is needed, with people prone to health cramps and heat exhaustion.

A heat index that hits 41 to 54 degrees Celsius spells danger with heat cramps and heat exhaustion more likely and if people continue with physical activity, they’re inviting a heat stroke.

Over 54 degrees Celsius, we have extreme danger, with heat stroke being imminent.

The dangers of exposure to heat are complicated. For example, physical activity under full sunlight can increase the heat index by up to 8 degrees Celsius. Older readers will remember the summers of our youth when air conditioning wasn’t that widely available, but the heat never seemed as oppressive as what we are seeing and feeling today, particularly in cities, and this is because we are experiencing the global climate emergency, which is worse in cities, concrete jungles that have very little green space available to deflect the heat.

Walk past parking lots and you will feel the full impact of a “heat island”—the sun hits the concrete with full force and radiates it.

I’ve already mentioned vulnerable groups such as the elderly, the pregnant, and the sick, and the list goes on and on (even menopausal women!) but, again, even a healthy person can put herself at risk if she’s dehydrated.

We tend to forget the water needs of our pets. Just refilling their water dishes isn’t as easy as it seems. I realized this when I was alone yesterday in the house and the dogs were all panting and as I gathered their water dishes to fill, I laughed as I realized I was panting as well and being extra cautious because I have vertigo and was recovering from a bad case of flu.

Only a few days earlier, my driver told me how many dogs had died in his community from dehydration, simply because there are still households that do not have piped-in water.

With so many dogs joining us on trips, make sure you’re ready for hydration needs. I use a “pup cup,” a wonderful contraption my kids got me from Shopee to store water, as well as food for travel. Remember, dogs and cats don’t sweat so their risks for dehydration are even higher than for humans. Signs of dehydration include dry gums with thick sticky saliva, dry nose, loss of skin elasticity, and reduced urine output.

Let’s get ready for the month of May ahead, when the heat index could worsen.

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TAGS: heat-related illness, summer, travel, water

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