Tamino: The Oz heat distribution – In Alice Springs, “the number of very hot days each year (100°F or hotter) has nearly tripled” since early 20th century

Desdemona Despair

By Tamino
19 January 2019

(Open Mind) – We’ve spoken before (as have many before us) of the fact that climate isn’t just about the average, it’s about the whole distribution (the probability distribution if you want to get technical).

We also emphasized that the tails of the distribution — the probabilities for extreme values (very very cold or very very hot, if we’re talking about temperature) can change profoundly when we shift the distribution left or right, without otherwise changing its shape; we illustrated this with July temperature in Moscow:

It set me to wondering, how do things look down under?

I got daily data from the Australian Bureau of Meteorology for over 100 stations across the continent (their “ACORN” data set), and searched them for “very hot days.” I defined a “very hot day” as one with a high temperature of 100°F (37.78°F) or higher. I hope the Aussies can forgive me for using a definition based on an arbitrary choice (triple-digits) for an arcane (Fahrenheit) temperature scale … but Americans understand it, and few can argue that 100°F or higher makes for a very hot day.

I counted how many hot days occur each year, defining the “year” as July-through-June so that summer (Dec-Jan-Feb for southern hemisphererians) won’t be split across years. Then I fit a straight line by least squares, just to test whether or not there’s a trend and which way it’s going. To be eligible, I insisted that a station must have had at least 5 hot days since records began (for most stations, the year 1910). […]

We can do exactly the same analysis for a station which is in a very hot part of Australia, Alice Springs. […]

The number of very hot days each year (100°F or hotter) has nearly tripled. All temperature from 37°C (98.6°F) and above are more likely. Note that about once a year they would reach 41°C (105.8°F) or more, but these days about once a year they’ll make it up to 43°C (109.4°F). Not only have heat waves gotten more frequent and hotter, in places like Alice Springs they’re reaching extremely dangerous levels. [more]

The Oz Heat Distribution