Peruvian fishermen named the phenomenon La Niña – the gift giver – because the cold, nutrient-rich water brought to the equatorial Pacific off South America is a boon to marine life, supporting a larger fish population and increasing the fishermen’s catch. Here in Australia the gift isn’t fish but rain but sometimes, as this year, it can be too much of a good thing.
The Australian Bureau of Meteorology provides an excellent history of La Niña event that helps to put the recent rainfall into perspective with the descriptions below describing those that have had the biggest impact.
La Niña: 1988 – 89
SST: Moderate to Strong
This was a strong La Niña which had a strong effect on the southeast half of the country, with April 1988 to July 1989 (Figure 1) rainfall in the highest decile for most New South Wales, much of South Australia and northern Victoria, and parts of southern and eastern Queensland. Much of Tasmania and western WA, together with parts of the far north also had falls in deciles 8 and 9 for this period. From April to December 1988 (Figure 2), above to very much above average rainfall fell across much of the country, but there was a marked break to this pattern over January and February 1989 (Figure 3), when much of the continent recorded totals in the lowest three deciles. However, typical La Niña conditions returned with a vengeance during the March to July 1989 (Figure 4) period when there were widespread falls in decile 10, including record high totals over a large fraction of SA.
Flooding was a regular occurrence during this La Niña, with flooding in Adelaide in May 1988, NSW, northern SA and western Queensland during July 1988, southeastern Queensland in September 1988, SA in March 1989 and central Queensland during April to May 1989. One of the more notable floods occurred in Victoria during November and December 1988 (Figure 5), with widespread flash flooding, particularly in the Melbourne and Gippsland areas. Several rivers broke their banks.
In December 1988 following the flooding, over 700 cases of Ross River virus were reported in Victoria, with the main affected area being the Gippsland region. In April 1989, following heavy rains in northeast Tasmania almost 60 cases of Ross River virus were reported.
|Figure 1. Apr 1988 – Jul 1989||Figure 2. Apr 1988 – Dec 1988||Figure 3. Jan 1989 – Feb 1989|
|Figure 4. Mar 1989 – Jul 1989||Figure 5. Nov 1988 – Dec 1988|
La Niña: 1973 – 76
SOI: Moderate to strong
SST: Moderate to strong
Following a relatively intense El Niño, and in perhaps the longest sustained period of La Niña conditions in the instrumental record, this strong La Niña had a strong effect on Australia, with excessive rainfall over much of the country. For the period from June 1973 until March 1976 (Figure 1), rainfall was above average over virtually the entire country, with more than half of the area east of WA recording its highest rainfall on record for this particular 34-month period. The particularly impressive feature of the rainfall during this period was the complete lack of significant dry periods; only two short periods are worth noting – June to July 1974 and May to June 1975. With an area-average of 760 mm, 1974 is Australia’s wettest year on record, while 1973 (651 mm) and 1975 (602 mm) are third and fifth wettest respectively.
The very wet 1974 (Figure 2) caused the most recent major outbreak of Murray Valley encephalitis in southeastern Australia, with 58 reported cases. Also during this La Niña, 400 – 500 cases of Ross River virus were reported, ranging in areas from South Australia’s Murray Valley region, to Queensland. Most of these cases occurred in SA. The extensive rain in early 1974 produced abundant growth in central Australia, and when it dried out in late spring 1974 it provided abundant fuel for widespread fires.
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In what was a remarkable period, the month of January 1974 (Figure 3) stands out, with record rainfall and widespread flooding in central and eastern Australia. In area-average terms it is the wettest month on record across Australia, the NT and Queensland, while it is the second wettest over SA and NSW. Many of the major river systems in these areas were flooded during this time. Towards the end of January, Tropical Cyclone Wanda crossed the coast near Brisbane and exacerbated the flooding in Queensland, including one of Brisbane’s worst floods on record. Several other cyclones caused flooding, such as Tropical Cyclone Una in December 1973, TC Zoe in March 1974, TC David in January 1976, TCBeth and Ex-Tropical Cyclone Alan in February 1976, and TC Dawn in March 1976 to name a few.
Another standout month was October 1975 (Figure 4) during which Victoria had its wettest month on record and extensive flooding, and a large area with highest on record falls. Most other parts of continental Australia had rainfall in the top decile, except for southwest WA, northern NSW, southern Queensland and scattered areas in the NT.
|Figure 1. Jun 1973 – Mar 1976||Figure 2. 1974||Figure 3. Jan 1974|
|Figure 4. Oct 1975|
La Niña: 1954 – 57
This La Niña had a strong effect across the eastern third of Australia. From April 1954 until January 1957 (34 months) (Figure 1), Queensland, NSW and Victoria all had over 70% of their areas in the highest decile of rainfall, with parts of these areas being highest on record falls.
In February 1955 (Figure 2) extensive flooding occurred in NSW, with almost all of the state’s river systems affected. As a result, 15 000 people were left homeless in the short term, 50 people died, 100 000 livestock died and there were large agricultural losses. Some of the worst flooding occurred at Branxton, just north of Newcastle, where flood waters were almost 4m deep, and towns such as Maitland were also largely inundated.
March 1956 – December 1956 (Figure 3) was a very wet period for the regions surrounding the Murray-Darling River System, with floods from May until December. 1956 was the wettest year on record for the Murray-Darling Basin. During this time there was a Ross River virus outbreak in April 1956, with over 2000 cases reported throughout South Australia, Victoria and NSW near the river system.
|Figure 1. Apr 1954 – Jan 1957||Figure 2. Feb 1955||Figure 3. Mar 1956 – Dec 1956|
La Niña: 1949 – 51
SOI: Moderate to Strong
A particularly wet La Niña, which probably classifies alongside 1916-1918 and 1973-1976 as those with the strongest effects. The oceanic signal of this event began in winter 1949 when cooling occurred along the equatorial Pacific, but it wasn’t until December 1949 that a consistent SOI signal became established. For the time period from December 1949 until February 1951 (Figure 1), much of eastern and northern Australia recorded above to very much above average rainfall. Notably, Queensland had 95% of its area in the top two deciles for this period, and NSW 76%, with significant parts being highest on record, especially over the eastern half of NSW. 1950 was the wettest year on record averaged over both Queensland and NSW as well as over the four eastern states that comprise eastern Australia, despite the fact that Tasmania had its eighth driest year on record.
Several cyclones hit the north-east coast in early 1950, with one in particular during March (Figure 2) causing widespread flooding. Winter 1950 (Figure 3) was especially wet in coastal NSW and southern Queensland, while spring 1950 (Figure 4) was wet across much of the region, with record falls across large parts of Queensland and NSW west of the Great Dividing Range.
The wet year of 1950 (Figure 5) also caused Murray Valley encephalitis to reappear in 1951 with 48 reported cases.
|Figure 1. Dec 1949 – Feb 1951||Figure 2. Mar 1950||Figure 3. Jun 1950 – Aug 1950|
|Figure 4. Sept 1950 – Nov 1950||Figure 5. 1950|
La Niña: 1916 – 18
Following the drought of 1911-1916, this long lasting La Niña produced highest on record falls for the 20-month period from June 1916 – January 1918(Figure 1) in regions of SA, Victoria, Tasmania, WA, NSW and a large area of Queensland. All the eastern states and SA had well over half of their area with rainfall in the highest 10% of the historical record during this time.
Queensland was hardest hit by this La Niña. Heavy rain during December 1916 caused flooding in Clermont in which most of the town was destroyed or swept away. Following the flood the town was rebuilt on higher ground.
In addition, two intense tropical cyclones affected Queensland in early 1918. Now known as the Mackay cyclone, this storm drenched the central Queensland coastal town with 1411mm of rainfall in three days. In March an even stronger cyclone made landfall over Innisfail, with widespread damage affecting the Cairns, Babinda and Atherton Tableland districts.
Heavy rain across Victoria in September 1916 not only caused extensive flooding, but aided in producing high wheat yields for the Mallee and Wimmera regions. In June 1917, there were floods in northeastern Victoria.
During the very wet year of 1917 (Figure 2), 114 cases of Australian “X” disease were reported in southeastern Australia, and another 67 cases in 1918. This was later said to be Murray Valley Encephalitis.
|Figure 1. Jun 1916 – Jan 1918||Figure 2. 1917|
La Niña: 1909 – 11
SOI: Moderate to Strong
This La Niña had a rather localised yet strong effect, with high falls in coastal Queensland, southeast SA, western Victoria and south west WA during May 1909 to April 1911 (Figure 1). The rest of the continent received mostly normal falls for this period, except for central Western Australia, which had well below average rainfall. During this time floods were frequent, with several events in the summer months in Queensland.
During August 1909 (Figure 2) northern and western Victoria, and parts of SA, had a significant flooding event, affecting several rivers. Winter 1909 was the third-wettest on record for Victoria. The summer of 1910-11 was also particularly wet through most of eastern Australia. From early to mid-1911, the continent began to dry, marking the beginning of the 1911-1916 drought, which affected most of Australia.
|Figure 1. May 1909 – Apr 1911||Figure 2. Aug 1909|