Don’t know. Certainly Mexico and Canada have had some extremely high temps in recent years.

https://www.visualcapitalist.com/cp/mapped-the-worlds-record-heat-waves/

But a high temp is not a ‘heatwave’, (The authors of that page certainly don’t understand what a ‘heatwave’ is.)

I didn’t see that the authors of our article defined their use of that term. There must be a standard definition within the climate discipline.

According to WPedia, "The IPCC defines heatwave as “a period of abnormally hot weather, often defined with reference to a relative temperature threshold, lasting from two days to months.” It also notes that "In the United States, definitions also vary by region. "

So I guess you’d have to write the authors to suggest that they define the terms they’re flinging around. The article also has a huge bibliography; maybe some of the older entries discuss the question.

Brittanica says: “No formal, standardized definition of a heat wave exists. The World Meteorological Organization defines it as five or more consecutive days during which the daily maximum temperature surpasses the average maximum temperature by 5 °C (9 °F) or more. Some countries have adopted their own standards … whereas the U.S. National Weather Service defines a heat wave as a spell of “abnormally and uncomfortably hot and unusually humid weather” spanning two days or more.” - https://www.britannica.com/science/heat-wave-meteorology

Maybe it’s in one of the references in the Wikipedia article: https://en.wikipedia.org/wiki/Extreme_event_attribution (that’s the EEA term they keep using).