Category Archives: Weather Communication

Heat wave definitions: if one doesn’t suit us, we will take another one

Last week we had a heat wave in Belgium. But just a day before it officially became a heat wave, it was already connected to Global Warming. The alarmist on duty is Jill Peeters, a Flemish weather woman: Jill Peeters warns: a heat wave like this one will occur once every 3 years (Dutch). In it a graph that shows heat waves in De Bilt (The Netherlands) are on the rise:

heatwave climate central

That’s odd. I have been looking for some time at the heat wave data of Belgium and the Netherlands, but as far as I could see there was no reason for alarm, on the contrary. This was nothing like I have seen in the heat wave data of the De Bilt weather station. Where did they get this result?

In a tweet she linked to Climate Central that described the analysis. They tried to find out how likely heatwaves became using “observational weather and climate data, weather forecasts and climate models”. Color me unimpressed.

Apparently they also were in quite a hurry, beside observations, they used forecasts and they presented their result in the beginning of the period in which heat waves occur and apparently couldn’t wait for a couple days… This made me guess there is an hidden agenda here. It is definitely not scientific.

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If you want to enjoy the warm weather at its best, go where the heatwave is!

Last week I got to hear that there was an heatwave in Belgium. That was odd, because I didn’t hear something of that kind in the news, nor on the meteo-website. I didn’t had much time to look into it at that time, so forgot about it for a couple days. Today I had some time on my hand and found myself looking for that announcement. It seemed to be on the VTM news of July 15, 2014.

In that news bulletin Jill Peeters (weather woman) declared a heatwave … for De Kempen. “De Kempen” is an area in the North East of Belgium. This is how it seemed to be announced (translated from Dutch):

“We officially define a heatwave when it is warmer than 25 degrees for five days in a row, from which three days are warmer than 30 degrees,” said Jill. “The coming days this will be the case in De Kempen. Tropical air is already entering our country.”

First, I can agree with her definition, except on one point. Officially a heatwave in Belgium is indeed defined as a period of at least 5 consecutive days in which the maximum temperature exceeds 25 °C (77 °F), provided that on at least 3 days in this period the maximum temperature exceeds 30 °C, but as measured … in Uccle … not somewhere in De Kempen.

Why is this so important? The definition of a heatwave is calibrated for a climatological location. Our definition of a heatwave would not make much sense for example in Spain (summer would be one continuous heatwave) or in Helsinki (there would hardly be heatwaves).

Belgium has a maritime climate, but De Kempen is a bit different. There is a sandy soil, which is drier than the regions at the coast or in the middle of Belgium (where Uccle is situated). This means that it warms up quicker there. The difference is mostly 1 °C or bit more, but can in some exceptional cases exceed 10 °C. The warmest temperature ever was measured in that region. The heatwaves of De Kempen and Uccle are not exactly comparable.

Secondly, the day the announcement was done, there wasn’t a heatwave yet, according to the definition. It only would become a confirmed heatwave in the “coming days” if the forecast was correct.

My first idea was that she wanted to declare a heatwave as soon as possible. She is known to be quite alarmist, although that doesn’t show much in her weather talks.

But I was very surprised to read this statement on the same page (translated from Dutch):

Those who wants to enjoy the warm weather at its best in the coming days, will have to go to De Kempen. Says Jill Peeters.

That was not what I expected. What happened to “Global Warming will give more extreme heatwaves” we all heard in the media only just a couple years ago? Was this the separation between her role as weather woman (bringing a weather event that people seem to be fond of) and that of alarmist (hyping the story to scare people into action)? I have to admit that the reactions of the public on heatwaves changed quite a bit. From “Ay ay ay, global warming is happening” to “Yippeekyay! Let’s enjoy this nice weather”. Or is the heatwave scare already replaced by something else?

Time will learn if some climatologist stands up and make some doom and gloom projections on heatwaves. Forecast is that next week temperatures will go up again. Probably, to be continued.