New South Wales, Victoria, Tasmania and South Australia are currently affected by a massive complex low pressure system, dropping temperatures and bringing rain, hail, wind and snow.
While complex low pressure systems like this come along every year or so, some Australians may be feeling whiplash after a particularly warm autumn.
Typically, as Victoria and Tasmania head into winter we see cold fronts that move from west to east, generating rain and thunderstorms. This weather system started off like that, but developed into a complex low that will stay with us for the rest of the week.
It’s the kind of weather system you see on average once every year or two. What is a little unusual is to see such a deep pool of cold Antarctic air so early in May. Canberra, for example, is forecast to have a maximum of 9℃ on Friday – which would be its coldest day in the first half of May since 1970.
In weather-speak, “complex” describes a weather system with an intricate structure. Starting as a cold front across Victoria and Tasmania, this complex low now has multiple low-pressure centres at the surface, and is interacting with a broad low-pressure system in the upper levels of the atmosphere. These upper and low-level weather systems reinforce each other.
The other factor contributing to the complexity is the warmer waters of the Tasman Sea. The East Australian Current brings warmer waters down the east coast, raising ocean surface temperatures in the Tasman Sea relative to the neighbouring Bass Strait and Southern Ocean. When these low pressure systems develop over the western Tasman Sea, that warm water provides a lot more energy through evaporation.
When all the elements align, with a cold front and its associated cold air mass moving over warm water, beneath an upper-level low in the same place providing reinforcement, a deep and complex low-pressure system can develop.
Difficult to predict
The Bureau of Meteorology usually has several days’ indication that a system like this may form, but development of multiple low-pressure centres at the surface makes it tricky to predict exactly where local impacts will strike.
These small-scale low-pressure centres influence exactly where the heaviest rain or strongest winds will be, as do features of the landscape like mountain ranges.
While we can make broad predictions of what may be on the way, it’s not until we get closer to the event that we can really start to be more specific about rainfall totals, wind speeds, and so on.
The Bureau gets minute-to-minute readings from our Automatic Weather Stations, but we have the ability increase the frequency of some of our measurements (for example, at the moment we have increased the frequency of weather balloon releases at Hobart airport), to get additional information about the atmosphere.
This system will move fairly slowly over the next couple of days, and different elements will impact different parts of Australia.
We’ve got cold air, wind and showers over Victoria and southern New South Wales at the moment, but there are parts of the east coast that are still quite warm today. Tasmania is starting to see windy conditions in Hobart and rain developing, and potentially heavy rain through the east of the state over the next couple of days.
Once the cold air moves further north into NSW we’ll expect snow at lower levels as far north as the Central Tablelands, and then as we move into the weekend the low pressure system will move out into the Tasman Sea.
We’ll then start to see swell increase, as the ocean responds to the weather system. Heavy swell and hazardous surf conditions could push well north along the NSW coast and potentially into southern Queensland by early next week.
Currently, severe weather warnings for wind have been issued across parts of South Australia, Victoria, New South Wales and Tasmania. Heavy rain warnings and flood watches are in place in Victoria, and flood watches and warnings are current in Tasmania as well.
Other specific warnings provide important information for those on the land – the Bureau has alerted sheep graziers, for example, to the impacts of cold, wet and windy conditions on exposed livestock.
While these warnings are all fairly standard for this kind of weather system, always follow the advice of emergency services. We’re the weather experts, but they’re certainly the experts on preparing for hazardous weather!
The post-Marcus chaos in Greater Darwin is not just “a real wake-up call”, but a typical case of lessons yet to be learned. For example, large shallow-rooted trees planted after Cyclone Tracy and overhead power lines brought down in the cyclone were both hazards that could have been avoided. Darwin is now engaged in a long, difficult and costly clean-up.
So was there complacency among some residents, as emergency services warned? Did infrastructure providers underestimate the threat? In hot and humid weather, over one-third of Darwin’s population went without power for several days and safe-to-drink tap water for 48 hours. Communication networks were patchy for days.
What was the reluctance in seeking immediate support from other states despite banks and insurers considering this a catastrophe? Was it due to Commonwealth disregard for the Top End in general?
How well has Darwin coped?
There have been at least two opposing views on the impact of the cyclone. The first is a more optimistic one, largely because no one got killed or seriously injured. Community members spontaneously helped one another in the immediate aftermath.
On this view, although preparedness might have varied, people in general were prepared. Power outages for a few days were a “first world problem”. Most households were ready, for example, to use camping gas cookers.
Volunteers visited and helped vulnerable groups such as aged and sick people. Emergency responders, defence staff and infrastructure restoration teams are working tirelessly to return the city to normalcy.
On the other hand, Marcus uprooted thousands of trees across Greater Darwin, mostly African mahoganies, which were planted for revegetation after Tracy.
Water was cut off in places. For about 48 hours people were urged to boil tap water before drinking, cooking or brushing teeth. The Health Department issued a warning about melioidosis, a life-threatening disease spread by contact with soil, mud and surface water.
Fallen trees blocked many roads and caused mild to severe damage to residential, commercial and public premises. Outdoor areas were cordoned off for safety.
At several locations, tree branches are still hanging dangerously over roads, pavements, parks and roofs. Anywhere in the city or suburbs, you see major and minor roads, parks and beachfronts dotted with uprooted trees and fallen branches. The roadside piles of logs and green waste are likely to remain there for some time, as their removal is not an “emergency priority”.
What does a city do with so much waste?
Waste facilities are struggling to cope. The morning after the cyclone, vehicles queued for hours at the green waste facility. It is yet to be ascertained if arrangements can be made to manage the huge quantities of green waste.
United Nations Environment Program (UNEP) guidelines note that waste debris presents opportunities as “either a source of income or as a reconstruction material, and [can] reduce burdens on natural resources that might otherwise be harvested for reconstruction”.
An evaluation of green waste would help understand its recovery value. Research suggests that disaster waste management can account for 5–10% of the total recovery costs, often exceeding that of health care and education.
In October 2004, a typhoon devastated Toyooka in Japan, producing 45,000 tonnes of waste – 1.5 years of the city’s usual waste production. The 2011 tsunami in Japan produced the equivalent of of 9 years’ worth of municipal solid waste in Iwate prefecture and 14 years’ worth in Miyagi prefecture.
What can Darwin learn from this?
Local government is considering removing mahogany trees, which were introduced after Tracy, because of their fast growth and the expansive shade their dense canopies provide.
Globally, environmental dimensions of disasters are less recognised compared with social and economic dimensions. However, the loss of dense trees and the valuable ecosystem services these offer calls for environmental recovery to be a priority as well.
A 2013 study reveals that large sums of taxpayers’ money is typically spent following disasters, whereas increasing pre-disaster investments can achieve cost savings and resilience.
As an example, the territory government is offering relief payments between A$250 and A$650 for households that were without power for 72 hours or more. The importance of putting power lines underground was recognised more than a decade ago but the work is incomplete due to lack of political will.
This is the time to ask questions such as: what will be the scale of devastation and cost and duration of recovery if a category 4 or 5 cyclone hits Darwin? The next cyclone after Marcus, Nora, was expected to be a category 4 storm but was downgraded to category 3 when it hit the western coast of Cape York on March 25.
Why not prioritise transformation of critical infrastructure, such as shifting all power lines underground? What role can cost-benefit analysis play to achieve resilience to category 4 or 5 cyclones and other natural disasters?
More broadly, how can we learn from the past? What are the new lessons we can take forward from Cyclone Marcus? And how do we inspire a city to work towards creating “Resilient Darwin’”?
This is an edited extract from The Weather Obsession by Lawrie Zion, published by Melbourne University Press.
When Olympic swimming champion Giaan Rooney was asked to fill in presenting the weather segment on Melbourne’s Channel Seven weeknight news program just before Christmas 2012, she was taken aback. She pointed out that she knew nothing about weather and that her credibility was in sport. “Don’t worry, just do the weather,” was the reply from the network. Six weeks later, the 30-year-old Rooney was invited to continue in the role, replacing the 52-year-old presenter and trained meteorologist David Brown, who had been presenting on Seven for 20 years.
As it turned out, Brown remained with the network and eventually went on to present the weather for Seven’s Sydney weeknight bulletin. But the switch from Brown to Rooney illustrates a dilemma that has never been resolved. Just who should present the weather on television?
Commenting on Rooney’s appointment soon after the announcement, the Sunday Herald Sun’s Susie O’Brien wrote:
…the old adage that people like a mature man to tell them the serious news and a pretty face to tell them the weather still seems to apply. The real question is why we need a nice-looking woman who isn’t a meteorological expert to tell us the weather at a time when climate issues have never been more
important. The fact that we are still having these debates is a sign we have a long way to go. Sadly, I think we will continue to see women used as decorations on network TV for a while to come.
What O’Brien saw as an anachronistic decision needs to be understood in the context of the role of weather segments in television news bulletins, and the changing demographics of broadcast news audiences.
Weather presenters have long been a crucial component of any television news team, and are promoted as such. For many in the audience, they’ve also been the main conduit of weather information. Ten years ago 90% of Australians received at least some of their weather information from television. This has since fallen to 71%, according to a Bureau of Meteorology survey. But that’s still a lot of eyeballs. And with their segments usually perched at the end of bulletins, the extent to which weather presenters connect with viewers helps to determine whether their station can carry the valuable news audience over to the start of the next program.
When it comes to sheer numbers, TV news audiences may have generally held up well with older viewers, but younger viewers aren’t drawn to these programs to anything like the extent that their parents were. The result is that around half the audience is over the age of 50, and therefore more likely to go for the familiar than the experimental. So while the steady evolution of graphics means that weather reports look very different now from how they appeared in the early days of television, the format has remained more predictable than the weather itself.
We all know the ritual: What happened today? What will happen tomorrow? And beyond tomorrow? Across the country? If it’s a local bulletin the state and/or city forecast will precede the sign-off. As Channel Nine Brisbane news presenter Andrew Lofthouse has put it: “The weather reports are still one of the constant reassuring things that people can rely on.” This might partly explain why changes to who presents the weather attract so much attention within the media itself.
Despite an overall tendency to play it safe, what this actually means tends to fluctuate, with appearance, personality and specialist credentials all deemed to be relevant factors to varying degrees. As O’Brien put it in the context of Brown’s replacement by Rooney: “Presumably Channel Seven has tired of the serious approach and in the midst of falling ratings is going for the well-worn route of installing an attractive female to freshen things up.”
Hiring attractive women as weather presenters is a time-honoured global tradition. Writing about the history of TV weather in America, Robert Henson points out that it became clear in the 1950s that women could be accepted as weathercasters, as long as the focus was kept on clothing, hairstyle or anatomy. “So began the brief ascendancy of ‘weathergirls’, a term that speaks volumes about the differences in status between these women and their male counterparts in weathercasting.”
But while the weathergirl craze abated in the United States by the early 1960s, in Australia, where television had been introduced relatively recently, it was just beginning. In 1961, an item in the Bureau’s in-house publication, Weather News, noted that in Brisbane, “the majority of stations appear to favour the glamour-girl type of telecaster for weather presentations”, and that “Bureau staff have had the pleasure of indoctrinating and briefing two ‘Miss Australias’ and one ‘Miss Queensland’ in the short time that television has been operating in this State”. The background training included explaining the need for weather information to be presented seriously and faithfully, “and particularly for the more glamorous the need to submerge their glamour behind the prosaic highs and lows”.
In 1965, Melbourne’s Channel 9 hired model Rosemary Margan to present the weather. One evening in 1969, she appeared in a fur coat before stripping to a bikini during her live segment, sparking a steady stream of responses from viewers. In the 1970s, when searching for a replacement for the then pregnant Margan, the station hired the 15-year-old schoolgirl Kerry Armstrong, whose job application had led them to believe she was 22. While often appearing in short, tight garments, Armstrong, who went on to become a celebrated actor, did on one occasion break away from the standard weather script, when she informed viewers that “due to the drought, 1,000 head of cattle died. But don’t worry, beachgoers, it’s going to be another great day tomorrow with a top of 35 degrees”.
Decades later, the “weather girl” tag has proved hard to shake, as current Melbourne Channel Nine weather presenter Livinia Nixon told The Age in 2010. “TV and radio are very much boys’ clubs; they’re industries that are still very, very male-dominated,” she says, acknowledging that a male who presents the weather is a weather man, whereas she is a “weather girl”. “I wonder at what point you lose the ‘girl’?” she asks, having presented the segment on Nine’s 6pm weeknight news since 2004. “What age do you have to reach to not be called a girl any more?”
What if the woman presenting the weather has a relevant tertiary qualification? Back at Seven in Melbourne, Giaan Rooney remained in the role of weather presenter until taking maternity leave, when she was replaced by model and television personality Jo Silvagni, who was in turn replaced in late 2014 by Jane Bunn – who, as it happens, is also a qualified meteorologist. Her appointment also attracted media attention. When Nixon was asked about her new on-air rival, she told the Herald Sun that she didn’t think this would lend Seven’s bulletin any more clout. “I think it’s fantastic that Jane’s a meteorologist – hats off to her for doing the hard yards – but I’m confident working in conjunction with the Bureau (of Meteorology),” she says. “I feel very confident relaying all the information we get from them. Their accuracy rate has gone up over the years.”
Did Nixon, who had replaced the veteran weather presenter Rob Gell on Nine in 2010, have a point? A trained meteorologist of either gender might make the weather segment seem more credible to some, but would they enhance the substantive quality of information that is delivered? Historically the Bureau has insisted that provision of its information comes with a requirement that the media doesn’t mess with the message. TV stations can and do use the services of private weather companies to provide graphics, but the actual forecasts are still meant to be broadly consistent with the Bureau’s. So whichever nightly news channel you watch, won’t the next-day forecast be essentially the same?
With this and others questions in mind, I went to Melbourne’s Seven studios in Docklands to meet Bunn. After completing a Bachelor of Science at Monash University and a Graduate Diploma in Meteorology, Bunn worked for the Bureau in Sydney before turning to presenting the weather on television. “I loved the forecasting part of it but hated it when the message was being changed in the
media by people who got their terms muddled, so I decided I wanted to present it,” she tells me, citing an incident where a forecast of “fine and mostly sunny” was abbreviated to “mostly fine”. “You can have trust in what we are saying because that message might be jumbled up elsewhere. You’re better off
getting your weather from a meteorologist than a presenter because you know it’s as good as it can be.”
But Bunn doesn’t simply recite the Bureau’s forecast. Before her main segment goes to air at 6.55pm she checks the forecast models from Europe and Australia, which are updated after the Bureau releases its late afternoon forecast, to see if there are developments that might require some additional interpretation. She also analyses those same models to take the Bureau’s seven-day forecast one step
further, providing viewers with an eight-day outlook.
For all her specialist knowledge, however, Bunn’s appearance has also been a talking point both in social media and in the gossip columns. “Jane Bunn had the farm boys panting when she was the weather girl on regional television,” began one Herald Sun story, before conceding that “she doesn’t fit the weather girl stereotype”. Bunn accepts that her image is to some extent constructed by others. When I bring up the subject of how she is characterised in social media, she points out that other people have considerable input into how she appears before the camera. “I’ve purposely made it so hair and make-up and wardrobe decide what I actually look like – and that allows me to concentrate on my craft which is forecasting.”
As well as presenting all the usual weather details, Bunn has the scope to discuss seasonal forecasts and weather news in her segment, which provides her with the opportunity to embed her meteorological knowledge in her reports. Despite such individual touches, however, weather presenters in Australia, including Bunn, stick far more closely to the official forecasts than their American counterparts. In the United States, it is commonplace for local TV stations to hire meteorologists to present the weather, and many of these develop their own forecasts, which may be based on National Weather Service (NWS) data, or on those of other private providers whose predictions may also differ from those of the NWS. And television has long been a much more popular source of weather forecasts than the NWS. A 2006 survey of more than 1,400 Americans found that 72% of them caught a local TV forecast at least once per day, but less than 20% obtained daily forecasts from NWS websites, with just 4% tuning in to National Oceanic and Atmospheric Administration (NOAA) Weather Radio each day.
It might be just as well that Australia has not gone down this track. As American data journalist Nate Silver has noted in the American context, “the further you get from the government’s original data, and the more consumer facing the forecasts, the less reliable they become. Forecasts ‘add value’ by subtracting accuracy.” This is particularly the case with precipitation predictions. Non-National Weather Service forecasters, it turns out, tend to overestimate the probability of rain. There is a logic of sorts to this “wet bias”, says Silver. “People don’t mind when a forecaster predicts rain and it turns out to be a nice day. But if it rains when it isn’t supposed to, they curse the weatherman for ruining their picnic.”
Any Lismore local will tell you that flooding is a fact of life in the Northern Rivers. In the floods of 1954 and 1974, the Wilsons River rose to a record 12.17 metres. This time around, the river peaked at 11.59m, breaching the flood levee built in 2005 for the first time.
So what are the conditions that caused those historic floods? And are they any different to the conditions of 2017?
Like the current flood, cyclonic rains also caused the 1954 and 1974 events. But unlike those past events, both of which were preceded by prolonged wet weather, almost all of the extreme rainfall from ex-Tropical Cyclone Debbie fell within 24 hours.
More interesting still is the fact that we are not currently experiencing La Niña conditions, which have historically formed the backdrop to severe flooding in eastern Australia.
During the event, 20 rainfall stations in Queensland and 11 sites in NSW recorded their wettest March day on record. Mullumbimby, in the Brunswick River catchment, received a staggering 925mm during March – over half the annual average in a single month – causing major flooding in the region.
The heaviest rainfall in the Wilsons River catchment was at Terania Creek, which received 627mm over March 30-31, 99% of it in the 24 hours from 3am on March 30. Lismore recorded 324.8mm of rain in the 18 hours to 3am on March 31, its wettest March day in more than 100 years. A little further out of town, floodwaters submerged the gauge at Lismore Airport, so unfortunately we do not have reliable figures for that site.
The main difference between the current flooding and the 1954 and 1974 floods is that the previous events both occurred against a background of sustained La Niña conditions. These tend to deliver above-average tropical cyclone activity and high rainfall totals, which increase flood risk.
During the early 1970s, Australia experienced the longest period of La Niña conditions in the instrumental record. This unleashed phenomenal deluges across virtually the entire country. By the end of 1973, many catchments were already saturated as the wet season started early, culminating in the wettest January in Australia’s rainfall records.
In 1974 the Indian Ocean was also unusually warm (what meteorologists call a “negative Indian Ocean Dipole (IOD) phase”), further enhancing rainfall in the region. When negative IOD events coincide with La Niña conditions in the tropical Pacific, the warm sea temperatures reinforce one another, resulting in more evaporation and increased rainfall. This double whammy resulted in the exceptionally wet conditions experienced across the country during 1974.
In January 1974, the Northern Territory, Queensland and Australia as a whole recorded their wettest month on record, while South Australia and New South Wales recorded their second-wettest January on record. Torrential monsoon rains in the gulf country of Queensland transformed the normally dry interior into vast inland seas, flooding all the way to Lake Eyre in the arid zone of South Australia.
In contrast, Tropical Cyclone Debbie formed under neutral conditions, rather than during a La Niña. In fact, the Bureau of Meteorology is currently on El Niño watch, meaning that there is double the normal risk of an El Niño event bringing low rainfall and high temperatures to Australia by mid-2017.
So, unlike the 1950s and 1970s, the current flooding happened despite the absence of conditions that have driven major flooding in the past. It seems extraordinary that such a damaging cyclone could develop under these circumstances, and deliver such high rainfall over such a short time. This suggests that other factors may be at play.
A rapidly warming climate means that storms are now occurring in a “super-charged” atmosphere. As temperatures increase, so does the water-holding capacity of the lower atmosphere. The oceans are also warming, especially at the surface, driving up evaporation rates. Global average surface temperature has already risen by about 1℃ above pre-industrial levels, leading to an increase of 7% in the amount of water vapour in the atmosphere.
Of course, it is hard to determine the exact impact of climate change on individual storms. However, climate scientists are confident about the overall trends.
Australia’s land and oceans have warmed by 1℃ since 1910, with much of this warming occurring since 1970. This influences the background conditions under which both extremes of the rainfall cycle will operate as the planet continues to warm. We have high confidence that the warming trend will increase the intensity of extreme rainfall experienced in eastern Australia, including southeast Queensland and northern NSW.
While it will take more time to determine the exact factors that led to the extreme flooding witnessed in March 2017, we cannot rule out the role of climate change as a possible contributing factor.
That potentially means longer and more severe droughts, followed by deluges capable of washing away houses, roads and crops. Tropical Cyclone Debbie’s formation after the exceptionally hot summer of 2016-2017 may well be a perfect case in point, and an ominous sign of things to come.
Tropical cyclone Debbie has made landfall in Queensland as a category 4 cyclone with winds of more than 150 kilometres per hour.
The cyclone crossed the coast near Airlie Beach on Tuesday afternoon. Reports of wind gusts in excess of 200km per hour and rainfall of more than 200mm of rain have been made in some areas along the central Queensland coast.
The Bureau of Meteorology forecasted an average to above-average number of Australian cyclones in its October severe weather outlook. Australia receives 11 cyclones on average each year, with about four of those in Queensland. Debbie is the fifth cyclone of the season for Australia as a whole and the most intense of the season so far.
Anomalously high moisture, warm ocean temperatures, and low environmental pressures seem to have created the conditions that allowed TC Debbie to form and grow in intensity.
Tropical cyclones are low pressure systems that form over warm tropical oceans. The warmth and moisture of the oceans are what gives a cyclone its energy. The low pressure, which meteorologists measure in “hectopascals”, draws in the surrounding warm, moist air, which then rises into deep thunderstorm clouds. As the air is pulled into the centre of low pressure, Earth’s rotation causes it to spin cyclonically and it continues to intensify.
TC Debbie formed at the eastern end of an active monsoon trough extending from the Indian Ocean across the top of Australia and into the Coral Sea. The monsoon trough is a region of low air pressure and thunderstorms that forms over northern Australia in the summer months, bringing with it the wet season. On March 22, a large region of active thunderstorms began to organise into a weather disturbance off the eastern tip of Papua New Guinea.
Over the following two days the thunderstorms organised about a circulation centre as sea level pressures began to drop and moist air converged into the area. By late on March 24 a tropical depression, a forerunner of a cyclone, had formed and begun to drift south, making a long S-shaped track.
Tropical Cyclone Debbie was named on March 25. It then came under the influence of the subtropical ridge, a zone of stable high pressure that gives much of Australia’s fine weather during the summer. This drove Debbie west-southwest towards the Queensland coast while it gradually intensified further.
Because of the relatively high amounts of moisture in the atmosphere, and relatively warm ocean waters, Debbie intensified to category 4 by 10 pm on March 27, with the strongest wind gusts reaching 225-280km per hour. On Tuesday afternoon Debbie was a strong category 4 cyclone with a central pressure of 943 hectopascals and surface sustained winds of 185 kilometres per hour. The Bureau of Meteorology downgraded TC Debbie to a category 3 at 4:00 pm EST.
To put Debbie in context, there has been only one cyclone since 1980 to have made landfall in Queensland with a lower central pressure. That was Yasi in 2011.
Of the 46 cyclones to have made landfall in Queensland since 1980, only three others arrived at the coast with pressures of less than 960 hectopascals: Dominic in 1982, Winifred in 1986, and Ingrid in 2005.
Tropical cyclone forecasters use a variety of tools to forecast the storm’s track, intensity, storm surge, and rainfall. Because it is difficult to obtain observations of wind at the ocean’s surface under a cyclone, meteorologists have developed tools based on satellite imagery to estimate a storm’s intensity, location, and where the strongest and most destructive winds are found.
Several models are also used to aid in making forecasts – from the complex numerical weather prediction models, to statistical models. Models start by using observations of the atmosphere, and then use these data to make a forecast.
Depending on their level of complexity the models can predict the future track, intensity, rainfall, wave height, and/or storm surge. The forecasters access all of this information to then make their forecast.
Cyclone forecasts have improved considerably over time. In particular, track forecasts have improved so that the 48-hour forecast is now more accurate than the 24-hour ones were back in the early 1990s. Track forecasting has become so reliable that the US National Hurricane Centre now produces 120-hour track forecasts.
Intensity forecasts have improved more slowly, but as models have become more refined and satellite technology has improved, the ability of forecasters to accurately estimate and predict intensity is also getting gradually better.
The prediction of rainfall, the extent of the damaging wind field, and storm surge forecasts are also slowly improving. Now that they are receiving more attention, we can expect considerable improvements in these over the next decade.
Liz Ritchie-Tyo, Associate Professor, School of Physical, Environmental, and Mathematical Sciences, UNSW
El Niño has arrived, it’s getting stronger, and it’s not about to go away soon. And already there are rumblings that this could be a big one. El Niño in Australia means warmer temperatures, and sometimes, but not always, drier conditions.
In 2014, some climatologists thought a big El Niño might have been on the cards. Ultimately, after some vigorous early warming in the Pacific, conditions only touched on El Niño thresholds. This year, with an event already established, climatologists are suggesting the odds are rising of an El Niño rivalling the record events of 1982 and 1997.
So what’s all the fuss about, and how are conditions different from last year?
Tropical Pacific Ocean temperatures are still rising
El Niño events are identified by equatorial Pacific Ocean temperatures. At the ocean surface, an El Niño is when these are sustained at about 0.8°C warmer than average. As we speak, temperature anomalies are exceeding twice that value.
In fact, we have just experienced twelve consecutive weeks with temperatures more than 1°C above average in all five of the key El Niño monitoring areas. The record was previously held by the 1997 El Niño, when this widespread warming lasted eight consecutive weeks.
But no two El Nino’s are exactly the same. Despite this warming in the tropical Pacific Ocean, in the Indian Ocean temperatures are far warmer than they were in 1997 (or 1982), which may mean different impacts for Australia. But more about that later.
Sea levels are dropping north of Australia
When sea surface temperatures in the central equatorial Pacific get warm enough, the atmospheric circulation shifts and the usually strong trade winds reduce, sometimes even reversing.
The direct consequence of the changing wind pattern is that the sea level in the western equatorial Pacific is no longer “piled up” by the trade winds. Low sea levels north of New Guinea (shown boxed) are strongly correlated with Nino3.4, which is the index that relates best to Australian climate.
At the peak (December) of the 1997 El Niño, the sea level in the western Pacific dropped nearly 30 cm. It is only August and already the sea level is nearly 25 cm below normal to the north of Australia.
Likewise, in the eastern Pacific, sea levels have risen by similar amounts as the weakened trades allow water to shift east. This half-metre difference in the normal sea level between the east and west is a classic strong El Niño signature.
A drop in sea level often means less water flows past Indonesia and down Australia’s west coast — weakening the Leeuwin Current and reducing the likelihood of coral bleaching in Western Australia.
The current (late July) average forecast is for continued warming peaking at a Niño 3.4 value of +2.7°C by December. Such a value would put 2015 alongside the big El Niño events in 1982 (+2.8°C) and 1997 (+2.7°C).
Last year the ocean began generating an El Niño but the atmosphere wouldn’t come to the party. This year the atmosphere is clearly responding.
Two exceptionally large westerly wind events have already occurred in the western equatorial Pacific this year, giving this El Niño a significant boost. Another wind event is forecast for August to kick the system along even further and add to the strength of this El Niño.
What does this mean for Australia?
Of the 26 El Niño events since 1900, 17 have brought widespread drought to Australia. In the big El Niño of 1982, drought devastated the eastern half of Australia and drove the devastating Ash Wednesday bushfires.
In contrast, the even stronger El Niño of 1997–98 brought more localised drought, with key rains in May and September meaning winter crops did reasonably well in most areas. Other years, such as 2002 and 1996, when weaker El Niño’s occurred, the drought was more severe.
For Australia, it’s not the size of El Niño that matters, it’s how it interacts with other rainfall drivers – such as sea surface temperatures around the continent and in the Indian and Southern Oceans, as well as random ‘weather noise’ – that governs the eventual rainfall over the continent.
What can we expect?
A significant El Niño event is currently underway, and there’s a chance it could rival the big events of 1982 and 1997. While this may increase the chance of drought and higher temperatures in eastern Australia, many other factors influence potential impacts.
We are already seeing that in the August–October Bureau of Meteorology seasonal outlooks, with the warmest June ocean temperatures on record in the southern Indian Ocean keeping the strengthening El Niño at bay by putting more moisture into the mid-levels of the atmosphere and changing weather patterns.
So what’s the final 2015 El Niño prediction?
The 2015 El Niño is already significant, and a big El Niño certainly remains a possibility. Widespread strong impacts haven’t (yet) raised their head for Australia and indeed, such as in 1997, may never do.
But managing El Niño is all about managing risk. The southern spring is the time when dry weather, frosts and heatwaves can hurt farmers and many others the most. And that’s when El Niño events, which raise the odds of these impacts, like to bite hardest.
The authors will be one hand for an Author Q&A between 12:30pm and 1:30 pm on Tuesday, August 11. Post your questions in the comments section below.
Survivors of Cyclone Pam on the South Pacific islands of Vanuatu are bracing for a lack of food over the coming months because crops were destroyed in the recent storm.
Much of the archipelago’s population relies on subsistence farming and when the monster cyclone ripped through the country last week it wiped out livelihoods as well as homes.
“There’s always a lot of attention in the beginning, the first few weeks of a big disaster. But now, we’re looking at a hunger gap over the next three to six months,” said World Vision’s Emergency Operations Manager in Vanuatu, Alex Snary.
Aid agencies are rushing to deliver desperately needed supplies, especially to communities on the remote outer islands, which are still out of contact.
At least 11 people were killed in the disaster and 3,3000 displaced.
“It’s almost miraculous [on Tanna Island] that there isn’t a large number of casualties, given…