On Tuesday, the KNMI will launch a new figure in their app: heat power. This way we know what the heat does to us per hour that day, so that we know when it is really too hot to exercise or work. “People will have to get used to the term,” said KNMI spokesperson Jet van Paassen.
Remi Lehmann, Elleke van Duin
Only looking at the temperature gives a distorted picture, the institute says. One heat is not the same as the other: a dry summer day of 30 degrees with a breeze feels very different from a damp day of 25 degrees without wind.
How is heat power calculated?
Heat power therefore combines temperature, humidity, solar radiation and wind into one figure, on a scale of 1 to 10. The figure is calculated based on the Dutch climate.
“How warm it feels to your body also depends on humidity, solar radiation and wind, and on your own fitness and age,” the KNMI spokesperson explains.
How you are dressed also plays a role, says Van Paassen. “If you are dressed lightly and you are sitting in the garden, that is fine. But if you are going to hoe, it is a different story. And for a firefighter who has to wear a thick suit at a heat force of, for example, 5, it is useful to know what he can expect. The heat force figure is therefore a supplement to the air temperature.”
Humidity and wind play a role
The heat power message includes additional information about the meaning of the scale. This way everyone can make their own decision for their activities that day. Van Paassen: “If you plan to go for a run, you can decide when it is best to do so: at 2 p.m. or better at 5 p.m.?”
“It’s not just about when it is at its warmest, but also about the humidity and wind. Because if it is 25 degrees and there was a pleasant breeze all day but the wind stops, it can suddenly be very warm and then you don’t want to run 10 kilometers.”
“Heat is an important and growing theme. We see that heat can have enormous consequences for the health of vulnerable groups, but also for sporting events and festivals,” says Van Paassen. “We must better prepare the Netherlands for climate change and therefore also for heat.”
Just as logical as wind power
The system must become as logical as the Beaufort scale for wind power. Boris Kingma of technical research institute TNO summarizes it clearly: “With wind force 12 everyone knows that you have to hope that your roof is still on, and with wind force 1 there is nothing wrong. From wind force 6 to 7 you have to pay attention. This is pretty much how heat power should also start to work.”
Which heat force should you be careful with?
When is the heat force too high? That is difficult to say, because how heat is experienced differs per person. A vulnerable elderly person can collapse at heat force 4, an experienced athlete may be able to withstand more.
What we do know: heat force 10 is rare and occurred in De Bilt recently thirty years only three times. More often in the south and east, but never in the north and along the coast. In the southeast of our country it only occurs once a year on average.
When KNMI warned of extreme heat last year and issued a code orange on July 1 and 2, most of the Netherlands reached heat force 8 on July 1. On July 2, the eastern part of the Netherlands reached heat force 9, while on the coast it dropped to 4.
What is the difference between heat power and sun power?
Some weather companies and apps already use the term sun strength or UV index. According to the KNMI, these are often based solely on solar radiation. Heat power therefore provides a broader picture.
And that is necessary, the authority says. Not only do we have to deal with heat more and more often, athletes can even get in the cold at 23 degrees problems come. According to the KNMI, this makes it necessary to develop a better warning system.
Van Paassen: “A heat wave does not automatically mean a high heat force. And it is not the case that a heat wave is on the way with a high heat force. That is possible, but not necessary, because they are separate elements. Heat wave only has to do with air temperature and heat force is much broader.”
Guidance in the workplace
The hourly index also offers a useful guideline for the workplace. If the heat increases from 2 p.m. this afternoon, a construction company can say, for example: we will start and stop a little earlier.
“Although we are of course not concerned with what employers should do with the heat power figure, we only provide as much information as possible, so that everyone can then work on it themselves,” concludes Van Paassen.