Seasonal Climate Summary for Australia and the Southern Hemisphere (Summer 2018–19): Extreme Heat and Flooding Prominent

CSIRO PUBLISHING Journal of Southern Hemisphere Earth Systems Science, 2021, 71, 147–158 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

Ben S. Hague A,B

ABureau of Meteorology, GPO Box 1289, Melbourne, Vic. 3001, Australia. Email: [email protected] BMonash 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 Ninõ 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 Ninã 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 Ninõ 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 Ninã. Although both metrics have values close to the El Ninõ 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 Ninõ 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 Ó BoM 2021 Open Access CC BY-NC-ND www.publish.csiro.au/journals/es 148 Journal of Southern Hemisphere Earth Systems Science B. S. Hague

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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 Nin˜a, 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 Nin˜o. 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 149

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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 Ninõ threshold and the blue horizontal line indicating the La Ninã threshold. 5VAR is plotted with monthly values and accompanying three-month averages with red horizontal line indicating the El Ninõ threshold and the blue horizontal line indicating the La Ninã 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. 150 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 76 76 Pacific Pacific 3 3

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–3 –3 23Indian 23Indian Ocean Ocean –4 –4 –4 –3 –2 –1 0 1 2 34 –4 –3 –2 –1 0 1 2 34 RMM1 Labelled dots for each day. Labelled dots for each day. RMM1 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 1 the summer 2018–19 period. Synoptic weather systems and Earth System Simulator (ACCESS) model . 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 cool SST anomalies being in the eastern Indian Ocean. It was anomalies which indicates periods of strong westerly wind 2 bursts in mid-December and mid-February. Winds are com- thehottestaustralsummeronrecordintheNOAA (Huang et al. 2020) dataset, second-highest in GISS3 (Lenssen et al. puted from ACCESS and anomalies with respect to the 22-year 4 1979–2000 NCEP climatology. 2019)andthirdintheHadCRUT4 dataset, using a simple

1For more information on the Bureau of Meteorology’s ACCESS model, see http://www.bom.gov.au/nwp/doc/access/NWPData.shtml 2https://www.ncdc.noaa.gov/cag/global/time-series/shem/land_ocean/3/2/2019–2019 3https://data.giss.nasa.gov/gistemp/tabledata_v4/SH.Ts þ dSST.txt 4https://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 151

OLR Totals: Average of 20181201 - 20190231

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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 80 100 120 140 160 180 200 220 240 260 280 300 320 OLR Anomalies: Average of 20181201 - 20190231

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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 152 Journal of Southern Hemisphere Earth Systems Science B. S. Hague

MSLP2.5 × 2.5 ACCESS OP. ANAL. (hPa) 20181201 0000 20190228 0000 (a)

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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 153

NCEP REANALYSIS; u 850hPa Anomalies; Daily–averaged 1-Dec-2018 to 28-Feb-2019, NCEP climatology (1979-2010)

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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

5http://www.bom.gov.au/climate/current/statement_archives.shtml 6The information in this paragraph has been summarised from NIWA (2019). 154 Journal of Southern Hemisphere Earth Systems Science B. S. Hague

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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

7The information in this paragraph has been drawn from the 2018 and 2019 annual climate summaries of the South African Weather Service (2019, 2020). 8ftp://sidads.colorado.edu/DATASETS/NOAA/G02135/south/monthly/data/ Seasonal Climate Summary: summer 2018–19 Journal of Southern Hemisphere Earth Systems Science 155

(a) (b)

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 Below average –2°C 2–3 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

6°C Temperature decile ranges 5°C Highest on 4°C record Very much 3°C 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 MeteorologyID code: Analyser Issued: 10/09/2020 © Commonwealth of Australia 2020, Australian Bureau of MeteorologyID 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 (Re´union 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 tropical 156 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

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 to Seasonal Climate Summary: summer 2018–19 Journal of Southern Hemisphere Earth Systems Science 157 historical riverine flood events, this event is notable as an References example of a tide-driven flood event, occurring with only Blunden, J., and Arndt, D. S. (Eds) (2020). State of the Climate in 2019. Bull. limited effects of statistically-extreme weather or ocean events. Amer. Meteor. Soc. 101, S1–S429. doi:10.1175/2020BAMSSTA Such events have been documented in the United States TEOFTHECLIMATE.1 (e.g. Ray and Foster 2016), but not yet documented in detail Bureau of Meteorology (2019a). Monthly Weather Review Australia in the Australian scientific literature – hence motivating its December 2018. Bureau of Meteorology, Melbourne. Available at inclusion here. http://www.bom.gov.au/climate/mwr/aus/mwr-aus-201812.pdf The high tide for 20 February was predicted to be the second- Bureau of Meteorology (2019b). Tropical Low 13U – Townsville and highest tide of the year. At this time Ex-Tropical Cyclone Oma northwest Queensland floods. Bureau of Meteorology, Brisbane. Avail- able at http://www.bom.gov.au/cyclone/history/Tropical_Low_13U.pdf was offshore, with some probability that it may move towards Bureau of Meteorology (2019c). North Queensland Monsoon Flood Report. Brisbane, which generated high interest on both conventional Bureau of Meteorology, Melbourne. Available at http://www.bom.gov. and social media platforms. This media interest resulted in this au/qld/flood/fld_reports/QLD_Monsoon_Trough_floods.pdf widespread coastal inundation in estuaries and tidal rivers along Bureau of Meteorology (2019d). Special Climate Statement 69— an the east coast being widely reported. Impacts were reported from extended period of heavy rainfall and flooding in tropical Queensland. Ku Ring Gai Chase National Park north of Sydney to Cairns in Bureau of Meteorology, Melbourne. Available at http://www.bom.gov. northern Queensland between 18 and 22 February, with the most au/climate/current/statements/scs69.pdf reports of flooding around Brisbane and the Gold Coast. The Bureau of Meteorology (2019e). Special Climate Statement 68—wide- maximum observed hourly sea level during this event was spread heatwaves during December 2018 and January 2019. Bureau of 2.78 m on 20 February, 17 cm above the minimum flood Meteorology, Melbourne. Available at http://www.bom.gov.au/climate/ current/statements/scs68.pdf threshold level defined by Hague et al. (2019). The top-of- Bureau of Meteorology (2019f). Monthly Weather Review Australia hour tide predictions generated using R TideHarmonics January 2019. Bureau of Meteorology, Melbourne. Available at http:// (Stephenson 2016) indicate that this height was 7 cm higher www.bom.gov.au/climate/mwr/aus/mwr-aus-201901.pdf than would have been expected during typical meteorological Bureau of Meteorology and CSIRO (2020). State of the Climate 2020. and oceanographic conditions (i.e. the non-tidal residual). A sea Commonwealth of Australia. Available at http://www.bom.gov.au/ level of 2.78 m is not a particularly rare occurrence in Brisbane – state-of-the-climate/documents/State-of-the-Climate-2020.pdf it has occurred for 94 hours (over 79 days) in the 40-year period Donald, A., Meinke, H., Power, B., Wheeler, M., and Ribbe, J. (2004). 1980–2019. Similarly, astronomical tides of at least 2.71 m have Forecasting with the Madden-Julian Oscillation and the applications for been predicted for 93 hours (over 84 days). Residuals of 7 cm or risk management. In ‘International Crop Science Congress (ICSC 2004): more are even more common, occurring approximately 17% of New Directions for a Diverse Planet, 26 September–1 October 2004, Brisbane, Australia’. Available at http://www.cropscience.org.au/ the time. icsc2004/poster/2/6/1362_donalda.htm Fetterer, F., Knowles, K., Meier, W. N., Savoie, M., and Windnagel., A. K. 5 Conclusions (2017). Sea Ice Index, updated daily. Version 3. Boulder, Colorado USA. The key meteorological and oceanographic events in the NSIDC: National Snow and Ice Data Center. doi:10.7265/N5K072F8. southern hemisphere summer of 2018–19 have been sum- [Accessed 10/09/2020]. marised herein. This includes the first published accounts of a Hague, B. S., Murphy, B. F., Jones, D. A., and Taylor, A. J. (2019). Developing impact-based thresholds for coastal inundation from tide moderate-intensity marine heatwave in the Tasman Sea during gauge observations. J. South. Hemisph. Earth Syst. Sci. 69, 252–272. January and a widely documented tide-only flooding event in doi:10.1071/ES19024 Brisbane, Australia. Further, we provide the broader climato- Hobday, A. J., Alexander, L. V., Perkins, S. E., et al. (2016). A hierarchical logical context for these and other key events and weather approach to defining marine heatwaves. Prog. Oceanogr. 141, 227–238. impacts. ENSO and IOD, the key drivers of climatic variability doi:10.1016/J.POCEAN.2015.12.014 on the seasonal scale for Australia, were in neutral conditions. Huang, B., Menne, M. J., Boyer, T., et al. (2020). Uncertainty estimates for However, extreme rainfall and temperatures were still observed sea surface temperatures and land surface air temperatures in NOAA- across Australia, and more broadly, the southern hemisphere. GlobalTemp version 5. J. Climate 33, 1351–1379. doi:10.1175/JCLI-D- Australia experienced its hottest summer on record and its 19-0395.1 hottest January on record which was 0.998C hotter than any IPCC (2014). Climate Change 2014: Synthesis Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the previously recorded month, with extreme heat centred on NSW Intergovernmental Panel on Climate Change (Eds R. K. Pachauri, and and Victoria. L. A. Meyer.) (IPCC: Geneva, Switzerland). Kanamitsu, M., Ebisuzaki, W., Woollen, J., Yang, S.-K., Hnilo, J. J., Fiorino, Conflicts of interest M., and Potter, G. L. (2002). NCEP-DOE AMIPII Reanalysis (R-2). Bull. The author declares no conflicts of interest. Amer. Meteor. Soc. 83, 1631–1643. doi:10.1175/BAMS-83-11-1631 Kuleshov, Y., Qi, L., Fawcett, R., and Jones, D. (2009). Improving preparedness to natural hazards: Tropical cyclone prediction for the Acknowledgements Southern Hemisphere. Adv. Geosci. 12(Ocean Science), 127–143. The author wishes to acknowledge Skie Tobin (Australian Bureau of doi:10.1142/9789812836168_0010 Meteorology) for assistance with development of Fig. 1 and Blair Trewin, Lenssen, N. J. L., Schmidt, G. A., Hansen, J. E., Menne, M. J., Persin, A., Naomi Benger and Avijeet Ramchurn (all Australian Bureau of Ruedy, R., and Zyss, D. (2019). Improvements in the GISTEMP Meteorology) for constructive reviews and feedback. This research did not uncertainty model. J. Geophys. Res. Atmos. 124, 6307–6326. receive any specific funding. doi:10.1029/2018JD029522 158 Journal of Southern Hemisphere Earth Systems Science B. S. Hague

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