Despite the headlines, there was no paranormal extreme in Perth last week — just a game called heatwave bingo
Perth set a sort of record last week for four days in February above 40C. The BOM and media paraparazzi glorified the latest heatwave, chasing it like it was a celebrity Kendall-Jenner-type-event when it was not that different to the heatwaves we’ve had before. Before it came, there were headlines about how it was coming, there were minute-by-minute graphs of degrees C, stories of people cooking cupcakes in hot cars, and there were projections about hypothetical bigger, longer heatwaves that might come, maybe one day, someday: look out for “Temperatures into the fifties”!
Chris Gillham points out that this record was made at the Perth Metro station. Few seemed to mention that 9km away, at Perth Airport similar kinds of heatwaves were pretty common and things had been hotter and lasted longer in years gone by. This year the four day average at the airport was 42C but in 1956 there were 5 days at an average scorching 43.7. In 1933 there was a six day heatwave of 42C average in Perth city. And there were other heatwaves a lot like this a couple of weeks earlier, in January. But who cares about January when we can talk about the effect of climate change on February…
With Heatwave Bingo, every year’s a winner
With bingo, someone has to win. Sooner or later one combo comes up. The secret with BOM Bingo is to have lots of bingo cards. The more combinations the better. Because heatwaves have no official definition, the meaning of the term can change each day. And there must be 400 flavours of 4, 5, 6 or 7 day heatwaves which are split by town, state, season or month. The cut off can be 35C, or days over 37C, 38C, 39C, or 40C. We are multicultural, we can do “100F” records too. Then there are so-called “Perth” heatwaves which apply to one site, one thermometer, and which may not exist at other sites in the same city. Some heatwave days the maximum temperature barely falls over the line, whatever the arbitrary temperature cutoff is this week, and maybe for only 20 minutes, but it counts in media inches, even if it doesn’t count any meaningful scientific way.
The permutations and combinations go quite feral. If we felt like it we could also dig into the minima and mean records — was it the hottest summer night ever? (Not so, indeed the week before had the coldest February morning
ever since 1935, — Thanks Warwick, Lance and Chris. Funnily, we didn’t hear about that record on the news, though it did get one minor line near the bottom this article. Imagine if it had been the hottest February night…)
Heatwaves by averages versus the arbitrary cut-off kind
Instead of counting days over a line, we could look at the average maximum temperature during clusters of hot days — it’s less arbitrary.
Which kind of heatwave is worse, one with four consecutive days with maxes above 40C, or the type with six consecutive days with an average maximum of 42C. The kind measured by averages may have a cool 34 degree day in the middle of a six day run of 43s (see Jan 1933)? What’s worse — apparently, whichever one is occurring now.
For dozens of research scientists and investigative journalists, the 399 odd non-records each month get a non-mention. Those losing bingo cards go quietly back in the box til next year, when their lucky combo may come up.
Here’s a graph of the worst 4-day average-maximum-heatwaves in Perth at the airport — (the data from before 1944 comes from the Perth CBD. See the footnote). Automatic electronic sensors were also installed in the last two decades, and they appear to artificially record higher temperatures. (See Bill Johnston’s analysis of the introduction of the automatic system and Perth temperatures]. So despite all the urban warming effect, and the electronic sensors, the hottest and longest average max heat-waves were in 1933, 1956 and 1961. If climate change caused the second worst February heatwave in central Perth, did it also cause the overall number of average-max-heatwaves to fall?
No luck on the five day bingo this year:
Spot the trend? No prizes for anyone saying that heatwaves are getting cooler in Perth:
Graphs with help from Geoff Sherrington
From Chris Gillham:
A bit more re Perth’s heatwave and supposedly most extreme summer ever … it’s worth reading The West Australian 11 Feb 1933 for a wrap on the 1933 heatwave including its four consecutive 40+ days which Perth equalled this week.
As noted in the story, the 1933 heatwave was also six consecutive days in which the temp exceeded 100F (37.8C), which beat the previous record of five consecutive 100F days in December 1899.
Perth Metro 1994-2016 has never had five consecutive days above 37.8C, let alone six.
It’s also worth comparing overnight minima in the first 11 days of 1933. They averaged 4.7C warmer than 2016 which is experiencing its most extreme summer in history at the peak of a supposedly large El Nino and with Indian Ocean SST above average.
The first 11 days of Feb 2016 included 9.9C, the coldest Feb night since 1935, and the first 11 days of 1933 included 29.3C, the hottest Feb night ever recorded in Perth (and 1.6C warmer than the hottest Feb night ever at Metro in 2004).
I’ve no idea how the Perth population is surviving this biblically extreme 2015/16 summer
There’s also been a media buzz about The “most extreme summer” ever with seven 40+ days
Chris Gillham does the numbers and finds again that Perth Airport has had many summers with such a run and hotter averages.
It’s correct that the seven 40+ days in the summer of 2015/16 beat the previous records of six 40+ summer days at Perth Metro and Regional Office since 1897. However, at Perth Airport there have also been seven days of 40+ this summer averaging 41.8C, and these can be compared with records since the airport site opened in 1945:
Seven 40+ days averaging 40.6C in 2010/11
Eight 40+ days averaging 41.7C in 2009/10
Eight 40+ days averaging 41.4C in 2006/07
Eight 40+ days averaging 41.5C in 1997/98
Seven 40+ days averaging 41.3C in 1995/96
Seven 40+ days averaging 42.6C in 1990/91
Seven 40+ days averaging 41.2C in 1983/84
Seven 40+ days averaging 41.0C in 1974/75
Ten 40+ days averaging 41.2C in 1961/62
Eight 40+ days averaging 42.5C in 1960/61
Eight 40+ days averaging 42.0C in 1955/56
Look at the long hot summer of 1962
*Heatwave graphs were compiled from BOM Tmax raw (not ACORN). Start 1/1/1897 at station 9034 (Perth regional office) to 2/6/1944. Then from Perth Airport 9021 to 2014. According to the BOM online data there was no heatwave in Feb 2014 or 2015. Comparing 9034 with 9021 in 1980 and 1992 Ave temps in Feb are 2C warmer at the airport. (We should see more records in recent times).