Average temperature trends across Western Australia
Below is an approximate 110 year comparison of average annual mean minimum and maximum temperatures at 32 different locations across Western Australia, including weather in the capital city of Perth.
The temperature averages have been extracted from the database publicly available at the Australian Bureau of Meteorology website for Western Australia, and from the first ever climate study conducted in the colony of Western Australia before 1900.
The annual mean minimum and maximum data are also linked below where available at locations surveyed by the Bureau of Meteorology in its analysis of "corrected" temperature trends from 1910 to 2008.
Average mean minimum and maximum temperatures are calculated from August 2018 to July 2019, the most recent 12 month timeframe. Albeit accurate, this recent 12 month data for each location should be considered statistically unreliable due to its brevity compared with "climate normals" that have typical year-to-year weather variations smoothed over standard periods (commonly 30 years).
This page is designed to provide a simple, convenient tool for people to observe temperature trends since weather records began in Western Australia, particularly in the context of perceived climate change.
Spotlights
The state of Western Australia covers 2,532,400 square kilometres and was proclaimed a British colony in 1829. The eastern border is 1,862 kilometres long and there is 12,889 kilometres of coastline. The highest elevation is Mt Meharry at 1,249 metres (4,098 feet). Western Australia had a population of 2.2 million in 2009, an increase of 17% since 2000.
Western Australia's capital of Perth is said to be on the coalface of global climate change, with 2007 Australian of the Year and Climate Change Commission chairman Tim Flannery predicting in 2004 that it may become the first city in the world to become a ghost metropolis due to lack of water (BBC, Sydney Morning Herald).
The chart above has been updated each month since 2009 to show the collective average minimum and maximum temperature anomalies over the previous 12 months at WA's 32 oldest weather stations (seven more than the 25 WA stations used to calculate BoM ACORN averages). The rolling 12 month anomalies are compared to their collective averaged maximum of 25.12C and minimum of 12.96C around the year 1900, based on annual temperature records within historical documents.
The chart demonstrates that WA's average temperatures have declined since early to mid 2016 and - after the 12 months to June and July 2017 registered a cooler average WA minimum than recorded 117 years earlier - have plateaued with a 2016-2018 mean temperature (19.7C) which is 0.6C cooler than 2013-2015 (20.3C). The bureau's official WA ACORN mean temperatures show a 2016-2018 average anomaly of +0.74C, which is 0.29C cooler than the 2013-2015 average ACORN anomaly of +1.03C. Across Australia, the bureau's official ACORN mean temperatures show a 2016-2018 average anomaly of +1.08C, which is 0.03C cooler than the 2013-2015 average ACORN anomaly of +1.11C.
Combined average mean temperatures in all 32 locations across Western Australia
Albany, Balladonia, Bridgetown, Broome, Bunbury, Busselton, Cape Leeuwin, Cape Naturaliste, Carnarvon, Derby, Donnybrook, Esperance, Eucla, Eyre, Geraldton, Halls Creek, Kalgoorlie, Katanning, Kellerberrin, Laverton, Marble Bar, Merredin, Mt Barker, Northam, Onslow, Perth, Rottnest Island, Southern Cross, Wandering, Wiluna, Wyndham, York
Minima
Late 1800s/early 1900s minima - 415 / 32 = 12.96
Late 1900s/early 2000s minima - 431.8 / 32 = 13.52
August 2018 - July 2019 minima - 425.09 / 32 = 13.28
- Average mean minimum in all 32 locations combined has risen 0.56 degrees C from early to late 20th century
- Average mean minimum in all 32 locations combined has risen 0.32 degrees C from early 1900s to 2019
Maxima
Late 1800s/early 1900s maxima - 804.1 / 32 = 25.12
Late 1900s/early 2000s maxima - 820.8 / 32 = 25.64
August 2018 - July 2019 maxima - 840.98 / 32 = 26.28
- Average mean maximum in all 32 locations combined has risen 0.52 degrees C from early to late 20th century
- Average mean maximum in all 32 locations combined has risen 1.16 degrees C from early 1900s to 2019
Note: Busselton weather station closed in November 2011 and all temperatures below from December 2011 are sourced to Busselton Aero. Read more ...
Note: Halls Creek Airport 2012 was renamed Halls Creek Meteorological Office and a new Halls Creek Airport 2079 became the primary site from 12 January 2017. To preserve location continuity, data for this page was sourced from site 2012 until December 2018 when the site ceased observations.
Note: The Bureau of Meteorology failed to record maximum temperatures at York 10311 in October, November and December 2017 and these missing values have a slight influence on the total averages calculated on this page.
Note: The Bureau of Meteorology failed to record temperatures at Balladonia 11017 in December 2017 and January 2018, and these missing values have a slight influence on the total averages calculated on this page.
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Hot spots
It should be noted that city and large town temperature readings may be influened by urban heat islands.
Also, it is difficult to compare all locations in Western Australia without accounting for temperatures in coastal cities and towns that are strongly influenced by ocean proximity. Overnight minima in coastal locations are several degrees warmer than inland locations because of the thermal blanket created by the ocean, and strong sea breezes reduce daytime temperatures along much of Western Australia's coastline during early-mid summer.
These natural variables have little impact on inland temperatures and this may influence comparative locational analysis.
About 83% of Western Australia's total population live in the 15 coastal cities and towns with temperatures recorded by the Australian Bureau of Meteorology since the year 1900.
The five coastal locations in Western Australia with populations above 20,000 (Albany, Bunbury, Busselton, Geraldton, Perth) have been major and expanding urban centres since colonial settlement in the early 19th century. Not surprisingly, the capital city of Perth (population 1.6 million in 2009) had the highest averaged increase in mean maximum temperature among all 32 locations, including pre-1910 data, over the hundred years (1.7 degrees C). However, it should be noted that changes in temperature recording location from Mt Eliza near the central city to the northern suburb of Mt Lawley mean Perth only has a reliable history beginning in 1994.
A temperature history comparison between the five large coastal centres and all other surveyed coastal locations suggests that the heat sink created by population and social infrastructure adds between .5 and 1 degree C to daytime maximum temperatures.
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Coastal locations with 2017 population above 20,000
Albany, Bunbury, Busselton, Geraldton, Perth
Minima
Late 1800s/early 1900s minima - 58.9 / 5 = 11.78
Late 1900s/early 2000s minima - 61.53 / 5 = 12.31
August 2018 - July 2019 minima - 58.63 / 5 = 11.73
- Average mean minimum in 5 locations combined has risen 0.69 degrees C from early to late 20th century
- Average mean minimum in 5 locations combined has fallen 0.05 degrees C from early 1900s to 2019
Note: Minima are affected by relocation of temperature ground stations in all five large coastal locations during the 20th century, with consequent falls in recorded overnight minima due to greater distance from the ocean and removal of the urban heat influence. Check all five locations below (except Busselton) to confirm significant falls in minima coinciding with ground station relocations (Albany, Bunbury, Busselton, Geraldton, Perth).
Maxima
Late 1800s/early 1900s maxima - 109.5 / 5 = 21.90
Late 1900s/early 2000s maxima - 115 / 5 = 23
August 2018 - July 2019 maxima - 115.83 / 5 = 23.17
- Average mean maximum in 5 locations combined has risen 1.10 degrees C from early to late 20th century
- Average mean maximum in 5 locations combined has risen 1.27 degrees C from early 1900s to 2019
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Coastal locations with 2017 population below 20,000
Broome, Cape Leeuwin, Cape Naturaliste, Carnarvon, Derby, Esperance, Eucla, Eyre, Onslow, Rottnest Island, Wyndham
Minima
Late 1800s/early 1900s minima - 174.8 / 11 = 15.89
Late 1900s/early 2000s minima - 180.62 / 11 = 16.42
August 2018 - July 2019 minima - 178.80 / 11 = 16.25
- Average mean minimum in 11 locations combined has risen 0.53 degrees C from early to late 20th century
- Average mean minimum in 11 locations combined has risen 0.36 degrees C from early 1900s to 2019
Maxima
Late 1800s/early 1900s maxima - 285.8 / 11 = 25.98
Late 1900s/early 2000s maxima - 291.5 / 11 = 26.50
August 2018 - July 2019 maxima - 299.68 / 11 = 27.24
- Average mean maximum in 11 locations combined has risen 0.52 degrees C from early to late 20th century
- Average mean maximum in 11 locations combined has risen 1.26 degrees C from early 1900s to 2019
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Inland temperatures
16 remaining inland towns
Balladonia, Bridgetown, Donnybrook, Halls Creek, Kalgoorlie, Katanning, Kellerberrin, Laverton, Marble Bar, Merredin, Mt Barker, Northam, Southern Cross, Wandering, Wiluna, York
Minima
Late 1800s/early 1900s minima - 181.4 / 16 = 11.33
Late 1900s/early 2000s minima - 193 / 16 = 12.06
August 2018 - July 2019 minima - 187.67 / 16 = 11.73
- Average mean minimum in 16 inland locations combined has risen 0.73 degrees C from early to late 20th century
- Average mean minimum in 16 inland locations combined has risen 0.40 degrees C from early 1900s to 2019
Maxima
Late 1800s/early 1900s maxima - 409.1 / 16 = 25.56
Late 1900s/early 2000s maxima - 421.96 / 16 = 26.37
August 2018 - July 2019 maxima - 425.46 / 16 = 26.59
- Average mean maximum in 16 inland locations combined has risen 0.22 degrees C from early to late 20th century
- Average mean maximum in 16 inland locations combined has risen 1.03 degrees C from early 1900s to 2019
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All locations except the five urban hot spots
Balladonia, Bridgetown, Broome, Cape Leeuwin, Cape Naturaliste, Carnarvon, Derby, Donnybrook, Esperance, Eucla, Eyre, Halls Creek, Kalgoorlie, Katanning, Kellerberrin, Laverton, Marble Bar, Merredin, Mt Barker, Northam, Onslow, Rottnest Island, Southern Cross, Wandering, Wiluna, Wyndham, York
Alternatively, the five major towns and cities can be compared with all 27 coastal and inland locations over 100 years.
As well as coastal vs inland natural variables, this comparison should create an upward bias on averages because all five towns and cities excluded from the 27 locations are in the coastal southern half of Western Australia, which is much cooler than the northern half and/or inland throughout the year.
Minima
Late 1800s/early 1900s minima - 356.1 / 27 = 13.18
Late 1900s/early 2000s minima - 369.63 / 27 = 13.69
August 2018 - July 2019 minima - 366.47 / 27 = 13.57
- Average mean minimum in 27 locations combined has risen 0.51 degrees C from early to late 20th century - compared to a rise of .56 degrees C for all 32 locations including Albany, Bunbury, Busselton, Geraldton, Perth (these five locations alone increased .68 degrees C).
- Average mean minimum in 27 locations combined has risen 0.39 degrees C from early 1900s to 2019 - compared to a rise of 0.32 degrees C for all 32 locations including Albany, Bunbury, Busselton, Geraldton, Perth (these five locations alone decreased -0.05 degrees C).
Maxima
Late 1800s/early 1900s maxima - 694.6 / 27 = 25.72
Late 1900s/early 2000s maxima - 704.5 / 27 = 26.08
August 2018 - July 2019 maxima - 725.14 / 27 = 26.86
- Average mean maximum in 27 locations combined has risen 0.36 degrees C from early to late 20th century - compared to a rise of .52 degrees C for all 32 locations including Albany, Bunbury, Busselton, Geraldton, Perth (these five locations alone increased 0.56 degrees C).
- Average mean maximum in 27 locations combined has risen 1.14 degrees C from early 1900s to 2019 - compared to a rise of 1.16 degrees C for all 32 locations including Albany, Bunbury, Busselton, Geraldton, Perth (these five locations alone increased 1.27 degrees C).
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Earliest colonial climate data compared to the latest RAW data
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The West Australian colony's earliest known meteorological analysis is The Climate of Western Australia 1876-1899 (PDF 25.4mb) compiled in 1901 by then Government Astronomer William Ernest Cooke. This document contains raw, unregulated data that is considered unreliable.
As the Government Astronomer explains in this historic document: "... it may be safely assumed that the results in this document give a close approximation to the truth; sufficiently so for all practical purposes, but scarcely to be considered quite accurate enough for the scientist."
Nevertheless, this compilation contains the only known official climate records for the Western Australia colony before 1900 and although recording discrepancies may have been common, these mistakes might either inflate or deflate the real temperatures (e.g. thermometers near warm buildings or in cool locations, although a common error was heat radiation from the ground).
The pre-1900 records are thus worth comparing with the most recent 30 years of regulated quality data from the Bureau of Meteorology, if only out of curiosity. See a detailed breakdown comparison of temperatures from the Cooke document.
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 (PDF 25.4mb)
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Minima
Towns surveyed for mean minimum night temperatures by the Government Astronomer that are included in the Bureau of Meteorology's quality control sites include Albany (11.4 C), Broome (20.1 C), Cape Leeuwin (14 C), Carnarvon (16 C), Derby (21 C), Esperance (11.3 C), Geraldton (13.9 C), Kalgoorlie (12.2 C), Katanning (8.4 C), Perth (12.3 C), Rottnest (13.3 C), Southern Cross (10.2 C) and York (11 C).
Combined, these 13 pre-1900 minima average 13.5 degrees C. Combining the same locations among the Bureau's quality controlled sites from 1979 to 2008, the average minimum is .37 degrees C warmer than 1876-1899 at 13.87 degrees C.
Combining the same 13 locations from August 2018 to July 2019, the average minimum is 0.37 degrees C warmer than 1876-1899 at 13.87 degrees C.
Maxima
Towns surveyed for mean maximum day temperatures by the Government Astronomer that are included in the Bureau of Meteorology's quality control sites include Albany (18.5 C), Broome (31.7 C), Cape Leeuwin (19.6 C), Carnarvon (28.7 C), Derby (33.7 C), Esperance (21.4 C), Geraldton (24.5 C), Kalgoorlie (25.5 C), Katanning (22.5 C), Perth (24.2 C), Rottnest, (22.2 C), Southern Cross (26 C) and York (24 C).
Combined, these 13 pre-1900 maxima average 24.80 degrees C. Combining the same locations among the Bureau's quality controlled sites from 1979 to 2008, the average maximum is 1.20 degrees C warmer than 1876-1899 at 26.0 degrees C.
Combining the same 13 locations from August 2018 to July 2019, the average maximum is 0.60 degrees C warmer than 1876-1899 at 25.40 degrees C.
Another historic document analysing Western Australia's past climate is Results of Meteorological Observations in Western Australia during 1908 (PDF 28mb) published in 1912 by then Commonwealth Meteorologist Henry Ambrose Hunt. Also of interest is The Climate and Weather of Australia (PDF 29mb), the first textbook on Australian Meteorology, published in 1913 by Henry Hunt and associates. See Hunt vs BoM temperature comparison for Australian capital cities.
For locations below that were monitored by Government Astronomer William Ernest Cooke, his recordings are listed as Pre-1900 vs recent 30 years mean temperature.
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Balladonia (BoM station 11017)
(elevation 151m, population 2006 - 50)
1891-1920 (20 years surveyed)
Average mean minimum 9.7
Average mean maximum 23.8
1921-1943 (22 years) / min 9.6 / max 24.2
1931-1943 (12 years) / min 9.5 / max 24.2
1951-1980 (16 years) / min 9.9 / max 25.1
1965-1990 (25 years) / min 9.9 / max 25.2
1971-2000 (30 years) / min 10.0 / max 25.3
1981-2010 (30 years)
Average mean minimum 10.1
Average mean maximum 25.3
12 months August 2018 - July 2019
Mean annual minimum 9.7
Mean annual maximum 25.0
BoM average means all available years
Mean annual minimum 9.9
Mean annual maximum 24.7
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Balladonia aerial picture
BoM historic annual minima from 1901
BoM historic annual maxima from 1901
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Mt Barker (BoM station 9581)
(elevation 300m, shire population 2006 - 2,971)
1905-1920 (16 years surveyed)
Average mean minimum 8.9
Average mean maximum 19.9
1921-1950 (30 years) / min 9.1 / max 19.8
1931-1960 (30 years) / min 9.1 / max 20.0
1941-1970 (30 years) / min 9.3 / max 20.3
1951-1975 (25 years) / min 9.5 / max 20.4
1961-1989 (17 years) / min 9.8 / max 20.6
1971-2000 (17 years) / min 10.1 / max 20.3
1981-2010 (22 years)
Average mean minimum 10.1
Average mean maximum 20.4
12 months August 2018 - July 2019
Mean annual minimum 9.0
Mean annual maximum 20.8
BoM average means all available years
Mean annual minimum 9.5
Mean annual maximum 20.2
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Mt Barker aerial picture
BoM historic annual minima from 1905
BoM historic annual maxima from 1905
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Northam (BoM station 10111)
(elevation 170m, shire population 2006 - 6,009)
1902-1920 (19 years surveyed)
Average mean minimum 10.7
Average mean maximum 25.0
1921-1950 (30 years) / min 11.1 / max 25.1
1931-1960 (30 years) / min 10.9 / max 25.3
1941-1970 (30 years) / min 11.0 / max 25.3
1951-1980 (29 years) / min 10.9 / max 25.3
1961-1990 (28 years) / min 11.2 / max 25.4
1971-2000 (28 years) / min 11.2 / max 25.5
1981-2010 (29 years)
Average mean minimum 10.8
Average mean maximum 25.7
12 months August 2018 - July 2019
Mean annual minimum 10.6
Mean annual maximum 25.9
BoM average means all available years
Mean annual minimum 10.9
Mean annual maximum 25.4
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Northam aerial picture
BoM historic annual minima from 1902
BoM historic annual maxima from 1902
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Wiluna (BoM station 13012)
(elevation 521m, shire population 2006 - 681)
1901-1930 (28 years surveyed)
Average mean minimum 14.0
Average mean maximum 28.8
1921-1950 (29 years) / min 14.1 / max 29.1
1931-1960 (30 years) / min 13.9 / max 29.0
1941-1970 (29 years) / min 13.9 / max 29.1
1951-1980 (29 years) / min 14.2 / max 29.1
1961-1990 (29 years) / min 14.7 / max 29.3
1971-2000 (29 years) / min 14.9 / max 29.3
1981-2010 (29 years)
Average mean minimum 14.8
Average mean maximum 29.6
12 months August 2018 - July 2019
Mean annual minimum 15.1
Mean annual maximum 30.9
BoM average means all available years
Mean annual minimum 14.3
Mean annual maximum 29.2
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Wiluna aerial picture
BoM historic annual minima from 1901
BoM historic annual maxima from 1901
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