NEIL HONEYMAN
FOR THE longest time, we have used the temperature in degrees Celsius as a measure of how hot we feel. For example, if we are told that the temperature is 35 degrees Celsius, then we know it is hot and that we shall feel hotter than when the temperature is “only” 30 degrees Celsius.
But it is not quite as simple as that.
Humidity is important also. Relative humidity, a measure of the amount of water vapor in the atmosphere, also affects how comfortable or uncomfortable we feel.
The Philippine Atmospheric, Geophysical, and Astronomical Services Administration (PAGASA) has recently introduced the concept of the “heat index”. For example, it was reported last week that the town of Catarman in Northern Samar experienced a 1PM temperature of 31.2 degrees Celsius and at the same time the humidity was recorded at 90 percent.
PAGASA told us that this corresponded to a 46° Celsius heat index. It further defined heat index as the level of heat or discomfort that a person experiences due to the combined effects of temperature and humidity. But this definition is qualitative. PAGASA does not tell us how it combines a 31.2 degrees Celsius and 90 percent humidity to give us a ‘heat index’ of 46° Celsius.
PAGASA needs to tell us the formula. A long time ago, the United States used a formula which it called ‘the uncomfortability index’ which was the average of the temperature in degrees Fahrenheit and the relative humidity. This registered that a warm, humid, day of 90 degrees Fahrenheit with a relative humidity of 80 percent gave us an uncomfortability index of 85. This formula enabled us to calculate how uncomfortable we were likely to feel.
We have not yet seen a similar formula corresponding to PAGASA’s heat index. We cannot, for example, combine a temperature of 31.2 degrees Celsius with a humidity of 90 percent to reach a heat index of 46° Celsius.
What is the formula?
A formula would be used in assessing how we feel for any given temperature/humidity combination. If the formula, the ‘heat index’ were sufficiently widespread and respected, we could use it to make decisions as to whether to send children home from school if it becomes too uncomfortable./PN
