In previous post I ended rather abruptly by saying that one of the problems with the vagueness of the definition of a heat wave, is that they are difficult to compare. What I meant by that is that those of the public, who don’t catch the nuances of those different definitions, think that is being talked about exactly the same thing, while they are in fact distinctly different.
For example, when the weather (wo)men in our region talk about a heat wave, they mean a period of five consecutive days with temperatures over 25 °C of which three days with temperatures over 30 °C at Uccle (Belgium) or De Bilt (the Netherlands). We have no real problem with that because in our country we are used to 20 °C, 25 °C temperatures or even higher. But we don’t cope well with 30+ °C temperatures, especially when they last more than a couple days. These are rare occurrences in our region and we are not used to them.
Bottom line: when our weather services declare a heat wave, it is hot and we need to take measures to cope with such (rare) heat. That is the significance of the definition: it captures the extremes of a region. Extremes that could have an impact those who are weak like small children, old people or those who are ill. In our current societal structure and in our climate, we just aren’t accustomed to these temperatures.
Now enter that new definition of a heat wave: the average temperature of three consecutive days. There is no regional threshold anymore, because the investigators wanted to compare between the different countries with different local definitions. Now we see an upwards going graph: