Extreme Rainfall Event in Western Australia

By: Christopher C. Burt , 9:54 PM GMT on December 17, 2012

Extreme Rainfall Event in Western Australia

The Australian Bureau of Meteorology just released (December 17th) a special statement concerning recent extraordinary rainfalls that occurred in the southwestern portion of Western Australia on December 10-13 (last week). All-time 24-hour precipitation records were broken at several locations when more than 8” (200 mm) of rain fell in less than 24 hours.

The special statement notes that “A deep surface trough interacted with a slow moving middle level low off the Western Australian west coast to produce widespread showers and thunderstorms across most of Western Australia from December 10 to 13.”



Maps of 24-hour rainfall amounts in Western Australia on December 12th and 13th. The heaviest rains fell in the extreme southwestern portion of the state on December 13th. Maps courtesy of the Australian Bureau of Meteorology.

The area most impacted was the Bunbury to Collie region located about 80 miles south of Perth. Collie measured 157.2 mm (6.19”) on December 13th(126 mm/4.96” of which fell in just 12 hours). The town not only smashed its previous December daily rainfall record of 42 mm/1.65” (set on December 24, 1987) but also broke its greatest 24-hour rainfall for any month in a 106-year long period of record. The amount also broke its December monthly record of 80.6 mm (3.17”) set in 1913.



Water floods into the Amaroo Primary School in Collie following a record 6” rainfall on December 13th. Photo by Katherine Hall.

Yourdamung Lake, 20 kl northeast of Collie measured 210.8 mm (8.30”), the 5th highest daily rainfall for any location, any month, in southwestern Australia (all-time record remains 239.8 mm/9.44” at Illalangi on March 10, 1917). The 210 mm at Yourdamung Lake also broke its all-time monthly December record. Flooding damaged 40 homes in Collie but was otherwise not severe.

This portion of Australia has a pleasant Mediterranean climate similar to the California south coast. Perth is Australia’s 4th largest city with a population of 1.8 million and is often cited as one of the world’s best places to live. It has an annual average rainfall of about 850 mm (33.5”) but December is normally one of its driest months with an average of just 13 mm (0.5”). So one can see how extraordinary this event is for the time of year. Ironically, the 2nd greatest rainstorm to occur in the region over the past 100 years happened almost exactly one year ago on December 11, 2011.



A thunderstorm brews over Perth. Most of the city’s precipitation falls between May and September. Photo by Mateusz Nowacki.

Christopher C. Burt
Weather Historian

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3. WunderAlertBot (Admin)
8:36 PM GMT on December 20, 2012
weatherhistorian has created a new entry.
2. blairtrewin
9:36 PM GMT on December 18, 2012
It's worth noting that although mean rainfall in the southwest of Western Australia is overwhelmingly concentrated in the winter half of the year, the highest extremes have been in the summer. The top six daily rainfalls in the region have all been between December and March.
Member Since: October 25, 2010 Posts: 0 Comments: 40
1. Neapolitan
10:35 AM GMT on December 18, 2012
Those are some astounding rainfall totals for that area. Wow!

One sentence in particular really stood out to me: "Ironically, the 2nd greatest rainstorm to occur in the region over the past 100 years happened almost exactly one year ago on December 11, 2011." It makes me wonder whether that's merely coincidence, or is evidence of some type of regime change. I suppose we'll be better able to answer that question as the next several years go by...

Thanks as always, Chris...

Member Since: November 8, 2009 Posts: 4 Comments: 15193

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About weatherhistorian

Christopher C. Burt is the author of 'Extreme Weather; A Guide and Record Book'. He studied meteorology at the Univ. of Wisconsin-Madison.