Seasonal climate summary for Australia and the southern hemisphere (summer 2018-19): extreme heat and flooding prominent
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CSIRO PUBLISHING
Journal of Southern Hemisphere Earth Systems Science
Seasonal Climate Summary
https://doi.org/10.1071/ES20009
Seasonal climate summary for Australia and the southern
hemisphere (summer 2018–19): extreme heat and flooding
prominent
A,B
Ben S. Hague
A
Bureau of Meteorology, GPO Box 1289, Melbourne, Vic. 3001, Australia.
Email: ben.hague@bom.gov.au
B
Monash University, School of Earth, Atmosphere and Environment, Clayton, Vic., Australia.
Abstract. This is a summary of the southern hemisphere atmospheric circulation patterns and meteorological indices for
summer 2018–19; an account of seasonal rainfall and temperature for the Australian region is also provided. January 2019
was Australia’s hottest month on record, nearly 18C warmer than any previous month. Impacts of heavy rain and floods
were reported in Australia, New Zealand and South American nations. Extreme terrestrial and maritime heatwaves
occurred in and around Australia and New Zealand. Case studies of the Australian heatwave, Queensland floods in January
and February, and a tide-driven coastal inundation event are considered.
Keywords: coastal inundation, extreme heat, flooding, heatwave, neutral ENSO season, positive OLR anomalies,
summer 2018–19.
Received 22 September 2020, accepted 27 December 2020, published online 2 February 2021
1 Introduction –7 this is often indicative of El Niño episodes, whereas
The Australian summer of 2018–19 was marked by widespread persistently positive values of SOI above þ7 are typical of a
above-average temperature and punctuated by extreme heat and La Niña episode. The 5VAR is a composite monthly ENSO
intense precipitation events in some areas. Here we summarise index, calculated as the standardised amplitude of the first
the climatic setting, the key climate drivers and diagnostics used principal component of the monthly Darwin and Tahiti mean
by the Bureau of Meteorology to characterise climate variability sea level pressure (MSLP) and monthly indices NINO3,
in the Australian region. Further, we investigate these patterns in NINO3.4 and NINO4 SSTs (Fig. 2b; Kuleshov et al. 2009).
the broader context of the southern hemisphere and summarise Values of the 5VAR that are more than one standard deviation
key meteorological parameters such as rainfall and temperature. are typically associated with El Niño for positive values, while
Finally, we identify some key extreme and noteworthy weather negative 5VAR values of a similar magnitude are indicative of
and climate events of the austral summer of 2018–19. Unless La Niña. Although both metrics have values close to the El Niño
otherwise stated, the main sources of information are analyses thresholds neither exceed it, meaning the summer of 2018–19 is
prepared by, or derived from datasets curated by, the Australian classified as a neutral ENSO season.
Bureau of Meteorology. The IOD is said to be in a positive phase when values of the
DMI (Fig. 2c) are greater than 0.48C, neutral when the DMI is
2 Climatic setting – drivers and diagnostics sustained between –0.48C and 0.48C and negative when DMI
In the southern hemisphere, the months of December 2018, values are less than –0.48C. The influence of the IOD on
January 2019 and February 2019 were not characterised by the Australian climate is typically weak during December to April.
influence of any specific climate drivers, with the El Niño This is due to the monsoon trough shifting south over the tropical
Southern Oscillation (ENSO), Indian Ocean Dipole (IOD) and Indian Ocean and changing the overall wind circulation, which
Southern Annular Mode (SAM) all taking values within the in turn prevents an IOD ocean temperature pattern from being
typical ranges (e.g. one standard deviation) of their respective able to form. This was true of summer 2018–19, classified as an
indices, as shown in sea-surface temperature (SST) patterns IOD neutral season.
in Fig. 1. The Madden–Julian Oscillation (MJO) is a tropical convec-
Fig. 2 shows representative values of the Southern Oscilla- tive wave anomaly which develops in the Indian Ocean and
tion Index (SOI), ENSO 5VAR Index (5VAR) and Dipole Mode propagates eastwards into the Pacific Ocean (Madden and Julian
Index (DMI) in the context of preceding seasons. If the Troup 1971, 1972, 1994). The MJO takes approximately 30 to 60 days
(1965) SOI (Fig. 2a) has sustained negative values of SOI below to reach the western Pacific, with a frequency of six to twelve
Journal compilation BoM 2021 Open Access CC BY-NC-ND www.publish.csiro.au/journals/es
B Journal of Southern Hemisphere Earth Systems Science B. S. Hague
(a)
SSTA (°C)
(b)
4.0
3.0
2.0
1.0
0.5
–0.5
–1.0
–2.0
–3.0
(c)
–4.0
Fig. 1. Sea-surface temperature analyses by the Bureau of Meteorology for (a) December 2018, (b) January 2019 and (c)
February 2019.
events per year (Donald et al. 2004). When the MJO is in an was active in these phases during late-December, early-
active phase, it is associated with areas of increased and January and again in late-January.
decreased tropical convection, with effects on the southern Outgoing longwave radiation (OLR) in the equatorial Pacific
hemisphere often weakening during early autumn, before Ocean can be used as an indicator of enhanced or suppressed
transitioning to the northern hemisphere. The diagnostic used tropical convection. Increased positive OLR anomalies typify a
operationally by the Bureau of Meteorology to identify the regime of reduced convective activity, a reduction in cloudiness
phase of the MJO is the Real-time Multivariate MJO index and, usually, rainfall. Conversely, negative OLR anomalies
(RMM, Wheeler and Hendon 2004). An MJO event in a specific indicate enhanced convection, increased cloudiness and chances
phase occurs when the line moves outside the central circle and of increased rainfall. During La Niña, decreased convection
into the octant corresponding with that phase. The RMM (increased OLR) can be seen near the Date Line, whereas
diagrams for October–December 2018 and January–March increased cloudiness (decreased OLR) near the Date Line
2019 are shown in Fig. 3. During December to February, MJO usually occurs during El Niño. Similarly, when Australia is
phases five and six typically correspond with wetter-than- under the influence of a negative IOD event, OLR anomalies are
average conditions across northern Australia, and the MJO negative over the eastern Indian Ocean where increased
Seasonal Climate Summary: summer 2018–19 Journal of Southern Hemisphere Earth Systems Science C
(a) 30
20
10
0
SOI
–10
–20
–30
–40
199 199 199 199 199 200 200 200 200 200 201 201 201 201 201
0 2 4 6 8 0 2 4 6 8 0 2 4 6 8
Year
(b) 3
2
1
5VAR
0
–1
–2
–3
199 199 199 199 199 200 200 200 200 200 201 201 201 201 201
0 2 4 6 8 0 2 4 6 8 0 2 4 6 8
Year
(c)
1.5
Dipole mode index (DMI)
1
0.5
0
–0.5
–1
–1.5
200 201 201 201 201 201 201 201 201 201 201
9 0 1 2 3 4 5 6 7 8 9
Year
Fig. 2. Time series of (a) SOI, (b) 5VAR and (c) DMI, placing the values of these diagnostic indicators in a longer-term context. SOI is
plotted with monthly values and accompanying five-month weighted averaging (6 for central month, 4 for months one offset from central
month and 1 for months two offset from central month), with red horizontal line indicating the El Niño threshold and the blue horizontal
line indicating the La Niña threshold. 5VAR is plotted with monthly values and accompanying three-month averages with red horizontal
line indicating the El Niño threshold and the blue horizontal line indicating the La Niña threshold. DMI is plotted with weekly values and
accompanying five-week moving mean with red horizontal line indicating the positive IOD threshold and the blue horizontal line
indicating the negative IOD threshold. Plots provided by Bureau of Meteorology.
D Journal of Southern Hemisphere Earth Systems Science B. S. Hague
(a) (b)
(RMM1, RMM2) phase space for 1-Oct-2018 to 31-Dec-2018 (RMM1, RMM2) phase space for 1-Jan-2019 to 31-Mar-2019
4 4
Western Western
7 6 7 6
Pacific Pacific
3 3
2 2
8 5 8 5
1 1
West. Hem.
West. Hem.
Continent
Continent
and Africa
Maritime
and Africa
Maritime
RMM2
RMM2
0 0
–1 –1
1 4 1 4
–2 –2
–3 –3
2 Indian 3 2 Indian 3
Ocean Ocean
–4 –4
–4 –3 –2 –1 0 1 2 3 4 –4 –3 –2 –1 0 1 2 3 4
Labelled dots for each day.
RMM1 RMM1
Labelled dots for each day.
Blue line is for Dec, green line is for Nov, red line is for Oct. Blue line is for Mar, green line is for Feb, red line is for Jan.
(C) Copyright Commonwealth of Australia 2019. Bureau of Meteorology (C) Copyright Commonwealth of Australia 2019. Bureau of Meteorology
2019 2019
Fig. 3. Phase-space representation of the Real-time Multivariate MJO index (RMM, Wheeler and Hendon 2004). (a) Shows daily values with the
months of October 2018 in red, November 2018 in green, and December 2018 in blue. (b) Shows daily values with the months of January 2019 in red,
February 2019 in green, and March 2019 in blue.
convection occurs. During summer 2018–19 there were positive 3 Summary of key meteorological and oceanographic
OLR anomalies over much of the land area in the southern variables
hemisphere, including Australia (Fig. 4). The climate drivers and their diagnostic indicators discussed
The MSLP pattern for summer 2018–19 is shown in Fig. 5a, above are not the sole influences on the observed meteorological
computed using data from the 0000 UTC daily analyses of the and oceanographic conditions in the southern hemisphere over
Bureau of Meteorology’s Australian Community Climate and the summer 2018–19 period. Synoptic weather systems and
Earth System Simulator (ACCESS) model1. MSLP anomalies changes already observed in the climate system due to anthro-
are shown in Fig. 5b, relative to 1979–2000, climatology pogenic greenhouse gas emissions (IPCC 2014; Bureau of
obtained from the National Center for Environmental Prediction Meteorology and CSIRO 2020) are two further notable con-
(NCEP) II Reanalysis data (Kanamitsu et al. 2002). The MSLP tributors of the state of the atmosphere and oceans at various
anomaly field is not shown over areas of elevated topography points in the season and across the season as a whole.
(grey shading). In general, the MSLPs over Australia and South
America were higher than usual and lower than usual near 3.1 Meteorological variables
Antarctica, broadly consistent with a positive SAM. For more
information on the SAM index from the Climate Prediction Temperatures were well above the long-term average over the
Center (NOAA), see http://www.cpc.ncep.noaa.gov/products/ southern hemisphere in summer 2018–19. Almost all land
precip/CWlink/daily_ao_index/aao/aao.shtml. Fig. 6 shows areas outside the Antarctic had seasonal mean temperatures
December 2018 to February 2019 low-level (850 hPa) wind near or above the 1981–2010 average, with the only significant
anomalies which indicates periods of strong westerly wind cool SST anomalies being in the eastern Indian Ocean. It was
bursts in mid-December and mid-February. Winds are com- the hottest austral summer on record in the NOAA2 (Huang
puted from ACCESS and anomalies with respect to the 22-year et al. 2020) dataset, second-highest in GISS3 (Lenssen et al.
1979–2000 NCEP climatology. 2019) and third in the HadCRUT44 dataset, using a simple
1
For more information on the Bureau of Meteorology’s ACCESS model, see http://www.bom.gov.au/nwp/doc/access/NWPData.shtml
2
https://www.ncdc.noaa.gov/cag/global/time-series/shem/land_ocean/3/2/2019–2019
3
https://data.giss.nasa.gov/gistemp/tabledata_v4/SH.Ts þ dSST.txt
4
https://www.metoffice.gov.uk/hadobs/hadcrut4/data/current/time_series/HadCRUT.4.6.0.0.monthly_sh.txt
Seasonal Climate Summary: summer 2018–19 Journal of Southern Hemisphere Earth Systems Science E
OLR Totals: Average of 20181201 - 20190231
60°N
30°N
0°
30°S
60°S
0° 30°E 60°E 90°E 120°E 150°E 180° 150°W 120°W 90°W 60°W 30°W 0°
−2
Wm
80 100 120 140 160 180 200 220 240 260 280 300 320
OLR Anomalies: Average of 20181201 - 20190231
60°N
30°N
0°
30°S
60°S
0° 30°E 60°E 90°E 120°E 150°E 180° 150°W 120°W 90°W 60°W 30°W 0°
W m−2
–45 –35 –25 –15 –5 5 15 25 35 45
(C) Copyright Commonwealth of Australia 2019, Bureau of Meteorology
Fig. 4. (a) Average OLR totals and (b) anomalies for summer 2018–19. Anomalies calculated with respect to a base
period of 1979–2010. Interpolated OLR data provided by the NOAA/OAR/ESRL PSD, Boulder, Colorado, USA.
Available at: http://www.bom.gov.au/climate/mjo/#tabs¼Cloudiness.
average of the December, January and February ensemble anomalies were highest or second highest in every state in
medians (Morice et al. 2012). There were 27 tropical cyclones December, except Queensland which ranked third highest.
in the 2018–19 season (World Meteorological Organization January was similarly hot, but in February top-10 mean
2020), the greatest number of tropical cyclones observed in a temperatures were recorded only in Western Australia and the
season since the 2008–09 season. The South Indian Ocean Northern Territory, despite the Australian average being the
region had 13 hurricane-intensity cyclones, the equal-highest fourth highest on record. All other mainland states recorded
number ever recorded. Two tropical cyclones in the above-average temperatures with Tasmania recording below-
Australian region that exceeded Category 2 strength (and average temperature, driven by cooler daytime maximum
hence, were Severe Tropical Cyclones) were Riley off the temperatures. Further discussion on January’s record-breaking
Kimberley coast in January, and Oma in the South Pacific in temperatures is included in Section 4.2.
February. During December, rainfall was below average in every state
In Australia, December 2018 broke records for highest and territory, except Victoria. This dry tendency continued
nationally averaged mean, maximum and minimum temperature throughout the summer with all states and the Northern Territory
and was also overall drier than average (Bureau of Meteorology being drier than usual in January and February, except Queens-
2019a). The mean maximum temperature across the month was land and Tasmania which recorded above-average rainfall totals
2.418C above average, and every state except Tasmania in February. Tasmania’s rainfall anomaly of –79% was its
recorded a mean maximum temperature between 28C and 38C second lowest on record. This intensified existing rainfall
above average. The Northern Territory recorded a 3.288C deficiencies. A summary of monthly state averages is provided
anomaly, which was its highest on record. Mean temperature in Table 1. Monthly maxima and averages are available on the
F Journal of Southern Hemisphere Earth Systems Science B. S. Hague
MSLP 2.5 × 2.5 ACCESS OP. ANAL. (hPa) 20181201 0000 20190228 0000
(a)
1035
1030
1025
1020
1015
1010
1005
1000
995
990
985
980
975
970
965
© Commonwealth of Australia 2019, Australian Bureau of Meteorology Issued: 01/03/2019
MSLP 2.5 × 2.5 ACCESS OP. ANAL.-NCEP2 (hPa) 20181201 0000 20190228 0000
(b)
20.0
17.5
15.0
12.5
10.0
7.5
5.0
2.5
0
–2.5
–5.0
–7.5
–10.0
–12.5
–15.0
–17.5
–20.0
No data
© Commonwealth of Australia 2019, Australian Bureau of Meteorology Issued: 01/03/2019
Fig. 5. (a) Southern hemisphere mean sea level pressure (MSLP) pattern and (b) anomalies for summer 2018–
19. Anomalies calculated with respect to base period of 1979–2000.
Seasonal Climate Summary: summer 2018–19 Journal of Southern Hemisphere Earth Systems Science G
NCEP REANALYSIS; u 850hPa Anomalies; Daily–averaged
1-Dec-2018 to 28-Feb-2019, NCEP climatology (1979-2010)
Dec 1
10
20
Jan 1
10
20
Feb 1
10
20
0° 40°E 80°E 120°E 160°E 160°W 120°W 80°W 40°W 0°
15.S–15.N m s–1
MW – Bureau of Meteorology –13 –11 –9 –7 –5 –3 –1 1 3 5 7 9 11 13
Fig. 6. Low-level (850 hPa) wind anomalies. Winds are computed from ACCESS and anomalies with respect to
the 22-year 1979–2000 NCEP climatology. Plot provided by Bureau of Meteorology (M. Wheeler pers. comm.).
Bureau of Meteorology website5. Fig. 7 shows the rainfall totals Island where data extend back to 1932. Rainfall across New
and deciles nationally, and Fig. 8 shows maximum and mini- Zealand was overall below-average especially on the South
mum temperature anomalies and deciles. Island, including in drought affected areas in the Tasman
New Zealand experienced its third-warmest summer on district. On the west coast, Hokitika recorded its driest summer
record, with all regions recording anomalies greater than in over 150 years. Some areas of the North Island recorded
0.58C, with Hastings in the Hawke’s Bay region of the North above-average rainfall, but this was mostly attributed to single
Island recording an anomaly of 2.48C, its third-highest value very wet days interspersing largely drier-than-usual conditions6.
since records began in 1965. Numerous locations recorded their South Africa recorded above-average temperatures and
highest summer average daytime maximum temperature includ- below-average rainfall across much of the region in December
ing at Appleby in the Tasman district of the northern South except for western parts of Northern Cape and Western Cape
5
http://www.bom.gov.au/climate/current/statement_archives.shtml
6
The information in this paragraph has been summarised from NIWA (2019).
H Journal of Southern Hemisphere Earth Systems Science B. S. Hague
(a) (b)
Rainfall (mm)
800 mm Rainfall decile ranges
600 mm Highest on
400 mm record
10 Very much
300 mm above average
200 mm 8–9 Above average
100 mm 4–7 Average
50 mm
2–3 Below average
25 mm Very much
1 below average
10 mm
Lowest on
5 mm record
1 mm
Australian rainfall analysis (mm) 0 mm
Rainfall deciles (using all avail. data)
1 December 2018 to 28 February 2019 1 December 2018 to 28 February 2019
Distribution based on gridded data
Australian Bureau of Meteorology
Australian Bureau of Meteorology
http://www.bom.gov.au http://www.bom.gov.au
© Commonwealth of Australia 2020, Australian Bureau of Meteorology ID code: Analyser Issued: 06/09/2020 © Commonwealth of Australia 2020, Australian Bureau of Meteorology ID code: Analyser Issued: 15/12/2020
Fig. 7. Rainfall (a) totals and (b) deciles. Decile ranges based on grid-point data with respect to all available data 1900–2020.
Table 1. Area averaged rainfall totals and maximum and minimum temperature anomalies and ranking (if in top 10 highest or lowest) for Australia
and individual states/territories over summer 2018–19
Region Rainfall Maximum temperature Minimum temperature
Average (mm) Ranking Anomaly (8C) Ranking Anomaly (8C) Ranking
Australia 144.60 10th lowest 2.60 Highest 1.67 Highest
Queensland 325.07 1.50 ¼8th highest 1.66 4th highest
New South Wales 88.92 10th lowest 3.61 Highest 3.21 Highest
Victoria 105.18 2.74 Highest 2.33 Highest
Tasmania 195.22 1.85 3rd highest 1.26 4th highest
South Australia 22.09 3.09 Highest 1.58 3rd highest
Western Australia 77.47 6th lowest 2.50 Highest 0.93 4th highest
Northern Territory 165.81 4th lowest 3.25 Highest 2.08 Highest
which had near-normal rainfall and typically cooler tempera- above the monthly average. This moderate-intensity marine
tures. Much of the eastern half of the country experienced heatwave (Hobday et al. 2016, using visualisation of Schlegel
maximum temperature anomalies of greater than 38C. These 2020) was sustained over much of the region over the summer
above-average temperatures and below-average rainfalls period but peaked in January 2019 as a strong to severe heatwave in
remained throughout January for much of the region although the region west of New Zealand. A more short-lived heatwave of
the area of greater than 38C anomalies contracted to northern and similar intensity and spatial extent also occurred near 2408E,
central parts of the country. February was milder, with approxi- 308S in December. The February Antarctic sea ice extent8 was
mately equal proportions of near-, below- and above-average 9.41 million km2, the fifth-lowest recorded since 1979 (Fetterer
maximum temperatures. Some areas were classified as ‘some- et al. 2017), resulting from the second-warmest year on record
what dry’ but for most of the country, precipitation was near- or (Blunden and Arndt 2020).
above-normal7.
4 Notable events and their impacts
3.2 Sea-surface temperatures This section is not intended to be exhaustive but rather provide
The SSTs were generally near or above average in the southern examples of high-impact or notable events and how these
hemisphere during the summer of 2018–19 (Fig. 1). Notably, affected societies, economies and the environment. Notable
a large area of above-average temperatures persisted in the Australian events that will be considered here are the extreme
Tasman Sea, peaking in January with a large area of þ4.08C heat in January and the extreme rainfall and flooding in
7
The information in this paragraph has been drawn from the 2018 and 2019 annual climate summaries of the South African Weather Service (2019, 2020).
8
ftp://sidads.colorado.edu/DATASETS/NOAA/G02135/south/monthly/data/
Seasonal Climate Summary: summer 2018–19 Journal of Southern Hemisphere Earth Systems Science I
(a) (b)
6°C
Temperature decile ranges
5°C Highest on
4°C record
3°C Very much
10 above average
2°C
1°C 8–9 Above average
0°C 4–7 Average
–1°C Below average
2–3
–2°C
Very much
–3°C 1 below average
–4°C Lowest on
–5°C record
Max. temp. anoms. (1961-1990 clim.) –6°C Minimum temp. deciles (all avail. data)
1 December 2018 to 28 February 2019 1 December 2018 to 28 February 2019
Australian Bureau of Meteorology Distribution based on Gridded Data
Australian Bureau of Meteorology
http://www.bom.gov.au http://www.bom.gov.au
© Commonwealth of Australia 2020, Australian Bureau of Meteorology ID code: Analyser Issued: 10/09/2020 © Commonwealth of Australia 2020, Australian Bureau of Meteorology ID code: Analyser Issued: 10/09/2020
(c) (d )
6°C Temperature decile ranges
5°C
Highest on
4°C record
3°C Very much
10
2°C above average
1°C 8–9 Above average
0°C 4–7 Average
–1°C
2–3 Below average
–2°C
1 Very much
–3°C below average
–4°C Lowest on
–5°C record
Max. temp. anoms. (1961-1990 clim.) –6°C Maximum temp. deciles (all avail. data)
1 December 2018 to 28 February 2019 1 December 2018 to 28 February 2019
Australian Bureau of Meteorology Distribution based on Gridded Data
Australian Bureau of Meteorology
http://www.bom.gov.au http://www.bom.gov.au
© Commonwealth of Australia 2020, Australian Bureau of Meteorology ID code: Analyser Issued: 10/09/2020 © Commonwealth of Australia 2020, Australian Bureau of Meteorology ID code: Analyser Issued: 10/09/2020
Fig. 8. Minimum temperature (a) anomalies and (b) deciles and maximum temperature (c) anomalies and (d) deciles. Decile ranges based on grid-point
data with respect to all available data 1900–2020.
February. Further discussions on these are included in Sec- New Zealand experienced several extreme weather events
tion 4.1 (rainfall and flooding) and Section 4.2 (the heatwave), that required evacuations of people in affected areas (NIWA
as is an example of a tide-driven coastal flooding event 2019). In February more than 1000 people were evacuated as a
(Section 4.3). large fire burned for 20 days in the Tasman region. One home
South America also experienced a heatwave in late-January was destroyed, and 2300 hectares were burnt. On 2 December,
and early February, culminating in the southernmost observa- heavy rain led to the evacuation of homes in Hamilton and over
tion of a temperature exceeding 308C at 53.88S in Rio Grande, 100 campers were evacuated from Waihi Beach as high tides
Argentina, the warmest temperature ever recorded so far south coincided with heavy rainfall on Christmas Eve. Tropical
(Blunden and Arndt 2020; World Meteorological Organization Cyclone Oma caused large agricultural impacts due to heavy
2020). Peru experienced its most intense heatwave for 30 years rains and floods in the South Pacific, especially Vanuatu and
and Paraguay recorded its hottest days on record, while New Caledonia (Blunden and Arndt 2020).
countries closer to the equator experienced droughts and water
shortages (Blunden and Arndt 2020). January 2019 also saw 4.1 Record flooding in tropical Queensland
major flooding in northern Argentina, Uruguay and southern Five named tropical cyclones were reported in the Australian
Brazil resulting in losses estimated at $US2.5 billion (World region between 1 December 2018 and 28 February 2019: Owen,
Meteorological Organization 2020). Kenanga, Penny, Riley and Oma. In addition to these, an un-
Indian Ocean islands experienced both extreme wet named tropical depression 13U that was embedded in the
(Seychelles had its second wettest year out of the last 47) monsoon trough brought flooding rains to much of northern
and extreme dry (Réunion Island had its driest rainy season Queensland. This was arguably the tropical weather system
on record), while Southern Africa was also generally dry associated with the most intense impacts for the season (Bureau
(Blunden and Arndt 2020). of Meteorology 2019b), despite it never reaching tropicalJ Journal of Southern Hemisphere Earth Systems Science B. S. Hague
Temp. Decile Ranges
Highest on
record
Very much
10 above average
8–9 Above average
4–7 Average
2–3 Below average
Very much
1 below average
Lowest on
record
Mean Temperature Deciles
January 2019
Distribution Based on Gridded Data
Australian Bureau of Meteorology
http://www.bom.gov.au
© Commonwealth of Australia 2020, Australian Bureau of Meteorology ID code: AWAP Issued: 03/02/2019
Fig. 9. January 2019 mean temperature deciles show large area of Australia as 10th decile or highest-on-record.
Daily mean temperature is calculated as the simple average of the daily minimum and daily maximum temperature.
cyclone intensity in the pressure- and wind-based metrics used services. Further information and technical details on the flood-
by the Bureau of Meteorology. Severe Tropical Cyclone Owen ing during January and February 2019 are provided in Bureau of
was the primary reason that north-eastern Queensland did not Meteorology (2019d).
suffer the same rainfall deficiencies as the rest of Australia in
December (Bureau of Meteorology 2019a). The flooding 4.2 Record heat in south-east and central Australia
associated with the 13U low-pressure system was centred
The summer of 2018–19 was the hottest on record for Australia,
principally off north-western Queensland and the Townsville
on average 0.868C hotter than any previously recorded summer.
region, with Townsville recording 1052.8 mm of rain in the
The heatwave conditions (defined by considering three-day
seven days to 4 February 2019, and 1259.8 mm in the ten days to
periods relative to climatological means and recent
8 February. These totals were 166.6 and 334.3 mm higher than
observations) were most extreme in January. January was
the previous seven- and ten-day accumulation records, set in
0.998C hotter than any previously recorded month, and centred
January 1998 and January 1953 respectively. Further informa-
on NSW, where it was more than 28C hotter than the previous
tion on the climatological and meteorological aspects of the
record. Victoria, Tasmania, Queensland and the Northern
heavy rainfall leading to this flood event are contained in Bureau
Territory also recorded their hottest month on record. The
of Meteorology (2019c).
heatwave was also exceptionally prolonged and persistent, with
This record-breaking rain produced record-breaking flood-
28 days exceeding the monthly 99th percentile across the
ing in Townsville and surrounds. The most significant impacts
summer, 2.5 times more often than in any previous summer.
were thousands of properties affected in Townsville, Giru (on
The area of highest-on-record and other deciles is shown in
the Haughton River) isolated for more than a week, the closure
Fig. 9. Further information, including climatological context
of key highways for over a week, and the spilling of the Burdekin
and meteorological information is available in Bureau of
Falls Dam. There was also substantial flooding elsewhere in
Meteorology (2019e). This period of extended heat was a factor
northern Queensland, with the Daintree River and the Daintree
that contributed to long-lived and large bushfires in Tasmania
Village recording their highest flood height in 118 years. Major
during January, with an area of approximately 2.6% of the total
flood thresholds were exceeded at Birdsville and Diamantina
area of Tasmania burnt as the result of several large fires, many
Lakes (Diamantina River), Sellheim (Burdekin River), Giru
in remote areas (Bureau of Meteorology 2019f).
(Haughton River), Townsville Aplin Weir (Ross River), Flora-
ville (Leichhardt River), Richmond and Walkers Bend (Flinders
River), Julia Creek (Julia Creek) and Daintree Village (Daintree 4.3 Tide-driven coastal inundation event on Australia’s east
River). Impacts consistent with this level were observed across coast
northern Queensland – closure of major rail and road routes, Although the impacts associated with this event may not have
flooding of buildings above the floor level and impacts to utility been as severe as other events this season, or compared toSeasonal Climate Summary: summer 2018–19 Journal of Southern Hemisphere Earth Systems Science K
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