Jonathan Nott, James Cook UniversityTropical Cyclone Seroja battered parts of Western Australia’s coast on Sunday night, badly damaging buildings and leaving thousands of people without power. While the full extent of the damage caused by the Category 3 system is not yet known, the event was unusual.
I specialise in reconstructing long-term natural records of extreme events, and my historic and prehistoric data show cyclones of this intensity rarely travel as far south as this one did. In fact, it has happened only 26 times in the past 5,000 years.
Severe wind gusts hit the towns of Geraldton and Kalbarri – towns not built to withstand such conditions.
Unfortunately, climate change is likely to mean disasters such as Cyclone Seroja will become more intense, and will be seen further south in Australia more often. In this regard, Seroja may be a timely wake-up call.
Seroja: bucking the cyclone trend
Cyclone Seroja initially piqued interest because as it developed off WA, it interacted with another tropical low, Cyclone Odette. This rare phenomenon is known as the Fujiwhara Effect.
Cyclone Seroja hit the WA coast between the towns of Kalbarri and Gregory at about 8pm local time on Sunday. According to the Bureau of Meteorology it produced wind gusts up to 170 km/hour.
Seroja then moved inland north of Geraldton, weakening to a category 2 system with wind gusts up to 120 km/hour. It then tracked further east and has since been downgraded to a tropical low.
The cyclone’s southward track was historically unusual. For Geraldton, it was the first Category 2 cyclone impact since 1956. Cyclones that make landfall so far south on the WA coast are usually less intense, for several reasons.
First, intense cyclones draw their energy from warm sea surface temperatures. These temperatures typically become cooler the further south of the tropics you go, depleting a cyclone of its power.
Second, cyclones need relatively low speed winds in the middle to upper troposphere – the part of the atmosphere closest to Earth, where the weather occurs. Higher-speed winds there cause the cyclone to tilt and weaken. In the Australian region, these higher wind speeds are more likely the further south a cyclone travels.
Third, most cyclones make landfall in the northern half of WA where the coast protrudes far into the Indian Ocean. Cyclones here typically form in the Timor Sea and move southward or south-west away from WA before curving southeast, towards the landmass.
For a cyclone to cross the coast south of about Carnarvon, it must travel a considerable distance towards the south-west into the Indian Ocean. This was the case with Seroja – winds steered it away from the WA coast before they weakened, allowing the cyclone to curve back towards land.
Reading the ridges
My colleagues and I have devised a method to estimate how often and where cyclones make landfall in Australia.
As cyclones approach the coast, they generate storm surge – abnormal sea level rise – and large waves. The surge and waves pick up sand and shells from the beaches and transport them inland, sometimes for several hundred metres.
These materials are deposited into ridges which stand many metres above sea level. By examining these ridges and geologically dating the materials within them, we can determine how often and intense the cyclones have been over thousands of years.
At Shark Bay, just north of where Seroja hit the coast, a series of 26 ridges form a “ridge plain” made entirely of one species of a marine cockle shell (Fragum eragatum). The sand at beaches near the plain are also made entirely of this shell.
The ridge record shows over the past 5,000 years, cyclones of Seroja’s intensity, or higher, have crossed the coast in this region about every 190 years – so about 26 times. Some 14 of these cyclones were more intense than Seroja.
The record shows no Category 5 cyclones have made landfall here over this time. The ridge record prevents us from knowing the frequency of less intense storms. But Bureau of Meteorology cyclone records since the early 1970s shows only a few crossed the coast in this region, and all appear weaker than Seroja.
Cyclones under climate change
So why does all this matter? Cyclones can kill and injure people, damage homes and infrastructure, cause power and communication outages, contaminate water supplies and more. Often, the most disadvantaged populations are worst affected. It’s important to understand past and future cyclone behaviour, so communities can prepare.
Climate change is expected to alter cyclone patterns. The overall number of tropical cyclones in the Australian region is expected to decrease. But their intensity will likely increase, bringing stronger wind and heavier rain. And they may form further south as the Earth warms and the tropical zone expands poleward.
This may mean cyclones of Seroja’s intensity are likely to become frequent, and communities further south on the WA coast may become more prone to cyclone damage. This has big implications for coastal planning, engineering and disaster management planning.
In particular, it may mean homes further south must be built to cope with stronger winds. Storm surge may also worsen, inundating low-lying coastal land.
Global climate models are developing all the time. As they improve, we will gain a more certain picture of how tropical cyclones will change as the planet warms. But for now, Seroja may be a sign of things to come.
This article is part of Conversation series on the nexus between disaster, disadvantage and resilience. Read the rest of the stories here.
When storms like Huricane Zeta menace the Gulf Coast, residents know the drill: Board up windows, clear storm drains, gas up the car and stock up on water, batteries and canned goods.
But how does wildlife ride out a hurricane? Animals that live along coastlines have evolved to deal with a world where conditions can change radically. This year, however, the places they inhabit have borne the brunt of 10 named storms, some just a few weeks apart.
As wildlife ecologists, we are interested in how species respond to stresses in their environment. We are currently studying how marsh birds such as clapper rails (Rallus crepitans) have adapted to tropical storms along the Alabama and Mississippi Gulf coast. Understanding how they do this entails wading into marshes and thinking like a small, secretive bird.
Mucky and full of life
Coastal wetlands are critically important ecosystems. They harbor fish, shellfish and wading birds, filter water as it flows through and buffer coastlines against flooding.
You wouldn’t choose a Gulf Coast salt marsh for a casual stroll. There are sharp-pointed plants, such as black needlerush, and sucking mud. In summer and early fall the marshes are oppressively hot and humid. Bacteria and fungi in the mud break down dead material, generating sulfurous-smelling gases. But once you get used to the conditions, you realize how productive these places are, with a myriad of organisms moving about.
Marsh birds are adept at hiding in dense grasses, so it’s more common to hear them than to see them. That’s why we use a process known as a callback survey to monitor for them.
First we play a prerecorded set of calls to elicit responses from birds in the marsh. Then we determine where we think the birds are calling from and visually estimate the distance from the observer to that spot, often using tools such as laser range finders. We also note the type of ecosystem where we detect the birds – for example, whether they’re in a tidal marsh with emergent vegetation or out in the open on mud flats.
Through this process we’ve been able to estimate the distributions of several species in tidal marshes, including clapper rails, least bitterns (Ixobrychus exilis) and seaside sparrows (Ammospiza maritima). We’ve also plotted trends in their abundance and identified how their numbers can change with characteristics of the marsh.
We’ve walked hundreds of miles through marshes to locate nests and to record data such as nest height, density of surrounding vegetation and proximity to standing water, which provides increased foraging opportunities for rails. Then we revisit the nests to document whether they produce young that hatch and eventually leave. Success isn’t guaranteed: Predators may eat the eggs, or flooding could wash them out of the nest and kill the developing embryos inside.
Rails in the grass
Our research currently focuses on clapper rails, which look like slender chickens with grayish-brown feathers and short tails. Like many other marsh birds, they have longish legs and toes for walking across soft mud, and long bills for probing the marsh surface in search of food. They are found year-round along the Atlantic and Gulf coasts.
Clapper rails typically live in tidal marshes where there is vegetation to hide in and plenty of fiddler crabs, among their frequent foods. Because they are generally common and rely on coastal marshes, they are a good indicator of the health of these coastal areas.
Water levels in tidal marshes change daily, and clapper rails have some adaptations that help them thrive there. They often build nests in areas with particularly tall vegetation to hide them from predators. And they can raise the height of the nest bowl to protect it against flooding during extra-high or “king” tides and storms. The embryos inside their eggs can survive even if the eggs are submerged for several hours.
When a tropical storm strikes, many factors – including wind speed, flooding and the storm’s position – influence how severely it will affect marsh birds. Typically birds ride out storms by moving to higher areas of the marsh. However, if a storm generates extensive flooding, birds in affected areas may swim or be blown to other locations. We saw this in early June when Hurricane Cristobal blew hundreds of clapper rails onto beaches in parts of coastal Mississippi.
In coastal areas immediately to the east of the eye of a tropical cyclone we typically see a drop in clapper rail populations in the following spring and summer. This happens because the counterclockwise rotation of the storms results in the highest winds and storm surge to the north and east of the eye of the storm.
But typically there’s a strong bout of breeding and a population rebound within a year or so – evidence that these birds are quick to adapt. After Hurricane Katrina devastated the Mississippi Gulf Coast in 2005, however, depending on the type of marsh, it took several years for rail populations to return to their pre-Katrina levels.
Now we’re radio-tagging clapper rails and collecting data that allow us to determine the birds’ life spans. This information helps us estimate when large numbers of birds have died – information that we can correlate with events like coastal hurricanes.
Tropical storms have shaped coastal ecosystems since long before recorded history. But over the past 150 years humans have complicated the picture. Coastal development – draining marshes, building roads and reinforcing shorelines – is altering natural places that support marsh birds.
Clapper rails and other species have evolved traits that help them offset population losses due to natural disasters. But they can do so only if the ecosystems where they live keep providing them with food, breeding habitat and protection from predators. Coastal development, in combination with rising sea levels and larger tropical storms, can act like a one-two punch, making it increasingly hard for marshes and the species that live in them to recover.
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Biologist Paul Ehrlich has compared species at risk to rivets on an airplane. You might not need every rivet in place for the airplane to fly, but would you fly it through a cyclone if you knew that 10% of its rivets were missing? What about 20%, or 30%? At some point, Ehrlich asserts, nature could lose so many species that it becomes unable to provide valuable services that humans take for granted.
We see coastal marshes as an airplane that humans are piloting through storms. As species and ecosystem services are pummeled, rivets are failing. No one knows where or how the aircraft will land. But we believe that preserving marshes instead of weakening them can improve the chance of a smooth landing.
Tropical cyclones are considered one of the most devastating weather events in Australia. But they’re erratic — where, when and how many tropical cyclones form each year is highly variable, which makes them difficult to predict.
In our new research published today, we created a statistical model that predicts the number of tropical cyclones up to four months before the start of the tropical cyclone season from November to April.
The model, the Long-Range Tropical Cyclone Outlook for Australia (TCO-AU), indicates normal to above normal tropical cyclone activity with 11 cyclones expected in total, Australia-wide. Though not all make landfall.
This is above Australia’s average of ten tropical cyclones per season, thanks to a climate phenomenon brewing in the Pacific that brings conditions favourable for tropical cyclone activity closer to Australia.
La Niña and tropical cyclones
As we’ve seen most recently with Tropical Storm Sally in the US, tropical cyclones can cause massive damage over vast areas. This includes extreme and damaging winds, intense rainfall and flooding, storm surges, large waves and coastal erosion.
“La Niña” is one phase of ENSO. It’s typically associated with higher than normal tropical cyclone numbers in the Australian region. And the Bureau of Meteorology’s weather and climate model indicates there’s a 95% chance a La Niña will be established by October this year.
Explainer: El Niño and La Niña
Around ten tropical cyclones occur in the Australian region every season, and about four of those usually make landfall.
Historically, La Niña has resulted in double the number of landfalling tropical cyclones in Australia, compared to El Niño phases. An “El Niño” event is associated with warmer and drier conditions for eastern Australia.
During La Niña events, the first tropical cyclone to make landfall also tends to occur earlier in the season. In fact, in Queensland, the only tropical cyclone seasons with multiple severe tropical cyclone landfalls have been during La Niña events.
Severe Tropical Cyclone Yasi, one of the most intense tropical cyclones to have hit Queensland, occurred during a La Niña in 2011. So did the infamous Severe Tropical Cyclone Tracy, which made landfall around Darwin in 1974, killing 71 people and leaving more than 80% of all buildings destroyed or damaged.
While naturally occurring climate drivers, such as La Niña, influence the characteristics of tropical cyclone activity, climate change is also expected to cause changes to future tropical cyclone risk, including frequency and intensity.
Australian tropical cyclone outlooks
Tropical cyclone outlooks provide important information about how many tropical cyclones may pass within the Australian region and subregions, before the start of the cyclone season. Decision-makers, government, industry and people living in tropical cyclone regions use them to prepare for the coming cyclone season.
The Australian Bureau of Meteorology has led the way in producing tropical cyclone outlooks for Australia, usually a couple of weeks before the official start of the tropical cyclone season.
But with monthly guidance up to four months before the start of the season, our new model, TCO-AU, is unmatched in lead time. It considers the most recent changes in ENSO and other climate drivers to predict how many tropical cyclones may occur in Australia and its sub-regions.
As a statistical model, TCO-AU is trained on historical relationships between ocean-atmosphere processes and the number of tropical cyclones per season.
For each region, hundreds of potential model combinations are tested, and the one that performs best in predicting historical tropical cyclone counts is selected to make the prediction for the coming season.
So what can we expect this season?
September’s TCO-AU guidance suggests normal to above normal risk for Australia for the coming tropical cyclone season (November 2020 – April 2021).
With an emerging La Niña and warmer than normal sea surface temperatures in the eastern Indian Ocean, 11 tropical cyclones are expected for Australia. There’s a 47% chance of 12 or more cyclones, and a probable range of between nine and 15.
For the Australian sub-regions, TCO-AU suggests the following:
above normal activity is expected for the Eastern region (eastern Australia) with four cyclones expected. Probable range between three and six cyclones; with a 55% chance of four or more cyclones
normal activity is expected for the Western region (west/northwest Western Australia) with six cyclones expected. Probable range between five and eight cyclones; 39% chance of seven or more cyclones
below normal activity is expected for the Northern region (northwest Queensland and Northern Territory) with three cyclones expected. Probable range between two and five cyclones; 37% chance of four cyclones or more
below normal activity is also expected for the Northwestern region (northwest Western Australia) with four cyclones expected. Probable range between three and six cyclones; 45% chance of five cyclones or more.
Guidance from TCO-AU does not and should not replace advice provided by the Australian Bureau of Meteorology. Instead, it should be used to provide a complementary perspective to regional outlooks and provide a “heads-up” in the months leading up to the start of and within the cyclone season.
Regardless of what’s expected for the coming cyclone season, people living in tropical cyclone regions should always prepare for the cyclone season and follow the advice provided by emergency services.
Tropical cyclones are among the most destructive weather systems on Earth, and the Southwest Pacific region is very exposed and vulnerable to these extreme events.
Our latest research, published today in Scientific Reports, presents a new way of predicting the number of tropical cyclones up to four months ahead of the cyclone season, with outlooks tailored for individual island nations and territories.
Tropical cyclones produce extreme winds, large waves and storm surges, intense rainfall and flooding — and account for almost three in four natural disasters across the Southwest Pacific region.
Currently, Southwest Pacific forecasting agencies release a regional tropical cyclone outlook in October, one month ahead of the official start of the cyclone season in November. Our new model offers a long-range warning, issued monthly from July, to give local authorities more time to prepare.
Most importantly, this improvement on existing extreme weather warning systems may save more lives and mitigate damage by providing information up to four months ahead of the cyclone season.
Tropical cyclones and climate variability
In 2016, Cyclone Winston, a record-breaking severe category 5 event, was the strongest cyclone to make landfall across Fiji. It killed 44 people, injured 130 and seriously damaged around 40,000 homes. Damages totalled US$1.4 billion — making it the costliest cyclone in Southwest Pacific history.
Tropical cyclones are erratic in their severity and the path they travel. Every cyclone season is different. Exactly where and when a tropical cyclone forms is driven by complex interactions between the ocean and the atmosphere, including the El Niño-Southern Oscillation, sea surface temperatures in the Indian Ocean, and many other climate influences.
Capturing changes in all of these climate influences simultaneously is key to producing more accurate tropical cyclone outlooks. Our new tool, the Long-Range Tropical Cyclone Outlook for the Southwest Pacific (TCO-SP), will assist forecasters and help local authorities to prepare for the coming season’s cyclone activity.
According to the latest long-range sea surface temperature outlook, there is a 79% chance that La Niña conditions could develop before the start of the 2020-21 Southwest Pacific cyclone season. La Niña conditions typically mean the risk of tropical cyclone activity is elevated for island nations in the western part of the region (New Caledonia, Solomon Islands and Vanuatu) and reduced for nations in the east (French Polynesia and the Cook Islands). But there are exceptions, particularly when certain climate influences like the Indian Ocean Dipole occur with La Niña events.
Improving existing tropical cyclone guidance
Current guidance on tropical cyclones in the Southwest Pacific region is produced by the National Institute of Water and Atmospheric Research, the Australian Bureau of Meteorology and the Fiji Meteorological Service. Each of these organisations uses a different method and considers different indices to capture ocean-atmosphere variability associated with the El Niño-Southern Oscillation.
Our research adds to the existing methods used by those agencies, but also considers other climate drivers known to influence tropical cyclone activity. In total, 12 separate outlooks are produced for individual nations and territories including Fiji, Solomon Islands, New Caledonia, Vanuatu, Papua New Guinea and Tonga.
Other locations are grouped into sub-regional models, and we also provide outlooks for New Zealand because of the important impacts there from ex-tropical cyclones.
Our long-range outlook is a statistical model, trained on historical relationships between ocean-atmosphere processes and the number of tropical cyclones per season. For each target location, hundreds of unique model combinations are tested. The one that performs best in capturing historical tropical cyclone counts is selected to make the prediction for the coming season.
At the start of each monthly outlook, the model retrains itself, taking the most recent changes in ocean temperature and atmospheric variability and attributes of tropical cyclones from the previous season into account.
Both deterministic (tropical cyclone numbers) and probabilistic (the chance of below, normal or above average tropical cyclone activity) outlooks are updated every month between July and January and are freely available.
Andrew Magee, Postdoctoral Researcher, University of Newcastle; Andrew Lorrey, Principal Scientist & Programme Leader of Climate Observations and Processes, National Institute of Water and Atmospheric Research, and Anthony Kiem, Associate Professor – Hydroclimatology, University of Newcastle
Public attention on the disastrous bushfire crisis in Australia will rightly continue for weeks to come. But as we direct resources to coping and recovery, we should not forget other weather and climate challenges looming this summer.
The peak time for heatwaves in southern Australia has not yet arrived. Many parts of Australia can expect heavy rains and flooding. And northern Australia’s cyclone season is just gearing up.
The events will stretch the ability of emergency services and the broader community to cope. The best way to prepare for these events is to keep an eye on Bureau of Meteorology forecasts.
Let it rain
But relief may be coming. The latest bureau outlooks suggest more normal summer conditions from February to April. If it eventuates, this would include more rain.
The arrival of drought-breaking rains is notoriously hard to predict – in the past, they have come any time between January and May. Global warming is also complicating seasonal climate predictions.
We all hope the rain arrives sooner rather than later, and eases the fire situation. But rain will bring other risks.
Continental-scale droughts such as that experienced over the past few years are often broken by widespread heavy rains, leading to an increased risk of flooding including potentially lethal flash floods. The decade-long Millenium drought that ended in 2009 was followed by two extremely wet years with serious flooding.
A similar situation was seen in Indonesia in recent days when very heavy rains after a prolonged drought produced disastrous floods and landslides.
The flood risk is exacerbated by the bare soil and lack of vegetation caused by drought, and by bushfires that destroy forest and grassland.
Australia’s north may be particularly hard hit. The onset of the tropical wet season has been very much delayed, as the bureau predicted. Over the last three months, some parts of the Australian tropics had their lowest ever October-December rainfall. But there are some suggestions widespread rain may be on its way.
Further south, drought-breaking rains can also be heavy and widespread, leading to increased flood risk. So even when the drought breaks and rains quell the fires, there will likely still be bouts of extreme weather, and high demand for emergency services.
Cyclones and heatwaves
Cyclones often bring welcome rains to drought-affected communities. But we should not overlook the serious damage these systems may bring such as coastal flooding and wind damage – again requiring intervention from emergency services.
And we are still a month away from the riskiest time for heatwaves in southern Australia. We’ve already had some severe heatwaves this summer. However they usually peak in the middle and end of summer, so the worst may be yet to come.
Lives have undoubtedly been saved this summer by improved forecasting of high temperatures and better dissemination of heatwave information by state and local governments. But after an already devastating early summer of fires and heat, warning fatigue may set in amongst both warning providers and the public. We must ensure heatwave warnings continue to be disseminated to populations at risk, and are acted on.
Be thankful for weather forecasters
The recent experience of farmers, fire fighters, water resource managers and communities illustrate the value of the service provided by the Bureau of Meteorology. Greatly improved weather and climate forecasting developed over the past few decades means communities can plan for and deal with our highly variable weather and climate far better than in the past.
Recent drought, fires and heatwaves – exacerbated by global warming – have been devastating. But imagine if we only had the limited weather forecast capabilities of even a few decades ago, without today’s high-speed computers to run weather forecast models, and satellites to feed in enormous amounts of data. How much worse would the impacts have been?
These forecasts have allowed heat alerts to be disseminated to vulnerable communities. Detailed information on weather conducive to fire spread has helped fire agencies provide more targeted warnings and direct resources appropriately.
Never before have weather forecasts been so readily available to the public. Here are ways you can use them to reduce risks to life and property during an extreme event:
- Listen to ABC local radio for emergency updates and detailed Bureau of Meteorology forecasts
- load your state fire service emergency app onto your phone and check it regularly. Or check out the information online, such as at the NSW Rural Fire Service’s Fires Near Me website
- check the bureau’s website for climate and weather forecasts
- download a short-range rainfall forecast app such as Rain Parrot onto your phone. These apps use the bureau’s radar data to make short-range forecasts of rainfall for your location, and notify you if rain is coming.
Global warming is already lengthening the fire season and making heatwaves more intense, more frequent, and longer. It is also increasing the likelihood of heavy rains, and making droughts worse.
We must keep adapting to these changing threats, and further improve our ability to forecast them. And the community must stay aware of the many weather and climate extremes that threaten lives and property.
Jonathan Pollock, Australian Bureau of Meteorology; Andrew B. Watkins, Australian Bureau of Meteorology; Catherine Ganter, Australian Bureau of Meteorology, and Paul Gregory, Australian Bureau of Meteorology
Northern Australia is likely to see fewer cyclones than usual this season, but hot, dry weather will increase the risk of fire and heatwaves across eastern and southern Australia.
The Bureau of Meteorology today released its forecast for the tropical cyclone season, which officially runs from November 1 to April 30.
Also published today is the October to April Severe Weather Outlook, which examines the risk of other weather extremes like flooding, heatwaves and bushfires.
Warmer oceans means more cyclones
On average, 11 tropical cyclones form each season in the Australian region. Around four of those cross the coast. The total number each season is roughly related to how much cooler or warmer than average the tropical oceans near Australia are during the cyclone season.
One of the biggest drivers of change in ocean temperatures is the El Niño–Southern Oscillation, or ENSO. During La Niña phases of ENSO, the warmest waters in the equatorial Pacific build up in the western Pacific and to the north of Australia. That region then becomes the focus for more cloud, rainfall and tropical cyclones.
But during El Niño, the warmest water shifts towards the central Pacific and away from northern Australia. This decreases the likelihood of cyclones in our region.
Explainer: El Niño and La Niña
And when ENSO is neutral, there is little push towards above or below average numbers of cyclones.
Temperatures in the tropical Pacific Ocean have been ENSO-neutral since April and are likely to stay neutral until at least February 2020. However, some tropical patterns are El Niño-like, including higher-than-average air pressure at Darwin. This may be related to the current record-strong positive Indian Ocean Dipole – another of Australia’s major climate drivers – and the cooler waters surrounding northern Australia.
The neutral ENSO phase alongside higher-than-average air pressure over northern Australia means we expect fewer-than-average tropical cyclones in the Australian region this season. The bureau’s Tropical Cyclone Season Outlook model predicts a 65% chance of fewer-than-average cyclones.
At least one tropical cyclone has crossed the Australian coast every season since reliable records began in the 1970s, so people across northern Australia need to be prepared every year. In ENSO-neutral cyclone seasons, this first cyclone crossing typically occurs in late December.
Other severe weather
While cyclones are one of the key concerns during the coming months, the summer months also bring the threat of several other forms of severe weather, including bushfires, heatwaves and flooding rain.
With dry soils inland, and hence little moisture available to cool the air, and a forecast for clear skies and warmer days, there is an increased chance that heat will build up over central Australia during the spring and summer months. This increases the chance of heatwaves across eastern and southern Australia when that hot air is drawn towards the coast by passing weather systems.
Likewise, the dry landscape and the chance of extreme heat also raise the risk of more bushfires throughout similar parts of Australia, especially on windy days. And with fewer natural firebreaks such as full rivers and streams, even greater care is needed in some areas.
Widespread floods are less likely this season. This is because of forecast below-average rainfall and also because dry soils mean the first rains will soak into the ground rather than run across the landscape.
However, as we saw in northern Queensland in January and February this year, when up to 2 metres of rainfall fell in less than 10 days, localised flooding can occur in any wet season if a tropical low parks itself in one location for any length of time.
Most of all, it’s always important to follow advice from emergency services on what to do before, during and after severe weather. Know your weather, know your risk and be prepared. You can stay up to date with the latest forecast and warnings on the bureau’s website and subscribe to receive climate information emails.
Jonathan Pollock, Climatologist, Australian Bureau of Meteorology; Andrew B. Watkins, Head of Long-range Forecasts, Australian Bureau of Meteorology; Catherine Ganter, Senior Climatologist, Australian Bureau of Meteorology, and Paul Gregory, BOM, Australian Bureau of Meteorology
This is an article from I’ve Always Wondered, a series where readers send in questions they’d like an expert to answer. Send your question to email@example.com
Who calls cyclones their names? – Guy Mullin, Mozambique.
In the Australian region, the Bureau of Meteorology gives tropical cyclones their name. You can write to the Bureau of Meteorology to suggest a cyclone name, but it is likely to be more than a 50-year wait.
Tropical cyclones are named so we can easily highlight them to the community, and to reduce confusion if more than one cyclone happens at the same time. The practice of naming tropical cyclones (or storms) began years ago to help in the quick identification of storms in warning messages. Humans find names far easier to remember than numbers and technical terms.
Clement Wragge began naming cyclones in 1887
Now, people ask us all the time how we come up with the names for tropical cyclones. It started in 1887 when Queensland’s chief weather man Clement Wragge began naming tropical cyclones after the Greek alphabet, fabulous beasts, and politicians who annoyed him.
After Wragge retired in 1908, the naming of cyclones and storms occurred much less frequently, with only a handful of countries informally naming cyclones. It was almost 60 years later that the Bureau formalised the practice, with Western Australia’s Tropical Cyclone Bessie being the first Australian cyclone to be officially named on January 6, 1964.
Other countries quickly began using female names to identify the storms and cyclones that affected them.
How cyclone names are chosen
While the world was giving female names to cyclones and storms, International Women’s Year in 1975 saw Bill Morrison, the then Australian science minister, recognise that both sexes should bear the shame of the devastation caused by cyclones. He ordered cyclones to carry both male and female names, a world first.
These days the Bureau is responsible for naming tropical cyclones in the Australian region, with the names coming from an alphabetical list suggested by the Australian public. These names alternate between male and female. The Bureau of Meteorology receives many requests from the public to name tropical cyclones after themselves, friends, and even pets.
The Bureau cannot grant all these requests, as they far outnumber the tropical cyclones that occur in the Australian region.
Curious Kids: What causes windy weather?
Cyclone Oma was named in Fiji
If a listed name comes up that matches the name of a well-known person, or someone in the news for a sensitive or controversial reason, the name is skipped to avoid any offence or confusion.
When a cyclone forms in another region, say near Fiji or in the Indian Ocean, and then travels into the Australian region, the original name given by that region’s weather agency is kept, such as 2019’s Cyclone Oma, which came from Fiji.
A list of cyclone names around the world can be found here.
2017 was the worst year on record for hurricane damage in Texas, Florida and the Caribbean from Harvey, Irma and Maria. We had hoped for a reprieve this year, but less than a month after Hurricane Florence devastated communities across the Carolinas, Hurricane Michael has struck Florida.
Coastlines are being developed rapidly and intensely in the United States and worldwide. The population of central and south Florida, for example, has grown by 6 million since 1990. Many of these cities and towns face the brunt of damage from hurricanes. In addition, rapid coastal development is destroying natural ecosystems like marshes, mangroves, oyster reefs and coral reefs – resources that help protect us from catastrophes.
In a unique partnership funded by Lloyd’s of London, we worked with colleagues in academia, environmental organizations and the insurance industry to calculate the financial benefits that coastal wetlands provide by reducing storm surge damages from hurricanes. Our study, published in 2017, found that this function is enormously valuable to local communities. It offers new evidence that protecting natural ecosystems is an effective way to reduce risks from coastal storms and flooding.
The economic value of flood protection from wetlands
Although there is broad understanding that wetlands can protect coastlines, researchers have not explicitly measured how and where these benefits translate into dollar values in terms of reduced risks to people and property. To answer this question, our group worked with experts who understand risk best: insurers and risk modelers.
Using the industry’s storm surge models, we compared the flooding and property damages that occurred with wetlands present during Hurricane Sandy to the damages that would have occurred if these wetlands were lost. First we compared the extent and severity of flooding during Sandy to the flooding that would have happened in a scenario where all coastal wetlands were lost. Then, using high-resolution data on assets in the flooded locations, we measured the property damages for both simulations. The difference in damages – with wetlands and without – gave us an estimate of damages avoided due to the presence of these ecosystems.
Our paper shows that during Hurricane Sandy in 2012, coastal wetlands prevented more than US$625 million in direct property damages by buffering coasts against its storm surge. Across 12 coastal states from Maine to North Carolina, wetlands and marshes reduced damages by an average of 11 percent.
These benefits varied widely by location at the local and state level. In Maryland, wetlands reduced damages by 30 percent. In highly urban areas like New York and New Jersey, they provided hundreds of millions of dollars in flood protection.
Wetlands reduced damages in most locations, but not everywhere. In some parts of North Carolina and the Chesapeake Bay, wetlands redirected the surge in ways that protected properties directly behind them, but caused greater flooding to other properties, mainly in front of the marshes. Just as we would not build in front of a seawall or a levee, it is important to be aware of the impacts of building near wetlands.
Wetlands reduce flood losses from storms every year, not just during single catastrophic events. We examined the effects of marshes across 2,000 storms in Barnegat Bay, New Jersey. These marshes reduced flood losses annually by an average of 16 percent, and up to 70 percent in some locations.
In related research, our team has also shown that coastal ecosystems can be highly cost-effective for risk reduction and adaptation along the U.S. Gulf Coast, particularly as part of a portfolio of green (natural) and gray (engineered) solutions.
Reducing risk through conservation
Our research shows that we can measure the reduction in flood risks that coastal ecosystems provide. This is a central concern for the risk and insurance industry and for coastal managers. We have shown that these risk reduction benefits are significant, and that there is a strong case for conserving and protecting our coastal ecosystems.
The next step is to use these benefits to create incentives for wetland conservation and restoration. Homeowners and municipalities could receive reductions on insurance premiums for managing wetlands. Post-storm spending should include more support for this natural infrastructure. And new financial tools such as resilience bonds, which provide incentives for investing in measures that reduce risk, could support wetland restoration efforts too.
Improving long-term resilience
Increasingly, communities are also beginning to consider ways to improve long-term resilience as they assess their recovery options.
There is often a strong desire to return to the status quo after a disaster. More often than not, this means rebuilding seawalls and concrete barriers. But these structures are expensive, will need constant upgrades as as sea levels rise, and can damage coastal ecosystems.
Even after suffering years of damage, Florida’s mangrove wetlands and coral reefs play crucial roles in protecting the state from hurricane surges and waves. And yet, over the last six decades urban development has eliminated half of Florida’s historic mangrove habitat. Losses are still occurring across the state from the Keys to Tampa Bay and Miami.
Protecting and nurturing these natural first lines of defense could help Florida homeowners reduce property damage during future storms. In the past two years our team has worked with the private sector and government agencies to help translate these risk reduction benefits into action for rebuilding natural defenses.
Across the United States, the Caribbean and Southeast Asia, coastal communities face a crucial question: Can they rebuild in ways that make them better prepared for the next storm, while also conserving the natural resources that make these locations so valuable? Our work shows that the answer is yes.
This is an updated version of an article originally published on Sept. 25, 2017.
Hurricane Irma (now downgraded to a tropical storm) caused widespread devastation as it passed along the northern edge of the Caribbean island chain and then moved northwards through Florida. The storm’s long near-coastal track exposed a large number of people to its force.
At its peak, Hurricane Irma was one of the most intense ever observed in the North Atlantic. It stayed close to that peak for an unusually long period, maintaining almost 300km per hour winds for 37 hours.
Both of these factors were predicted a few days in advance by the forecasters of the US National Hurricane Center. These forecasts relied heavily on modern technology – a combination of computer models with satellite, aircraft and radar data.
Forecasting is getting better
Although Irma was a very large and intense storm, and many communities were exposed to its force, our capacity to manage and deal with these extreme weather events has saved many lives.
There are many reasons for this, including significant construction improvements. But another important factor is much more accurate forecasts, with a longer lead time. When Tropical Cyclone Tracy devastated Darwin in 1974, the Bureau of Meteorology could only provide 12-hour forecasts of the storm’s track, giving residents little time to prepare.
These days, weather services provide three to five days’ advance warning of landfall, greatly improving our ability to prepare. What’s more, today’s longer-range forecasts are more accurate than the short-range forecasts of a few decades ago.
We have also become better at communicating the threat and the necessary actions, ensuring that an appropriate response is made.
The improvement in forecasting tropical cyclones (known as hurricanes in the North Atlantic region, and typhoons in the northwest Pacific) hasn’t just happened by good fortune. It represents the outcome of sustained investment over many years by many nations in weather satellites, faster computers, and the science needed to get the best out of these tools.
Tropical cyclone movement and intensity is affected by the surrounding weather systems, as well as by the ocean surface temperature. For instance, when winds vary significantly with height (called wind shear), the top of the storm attempts to move in a different direction from the bottom, and the storm can begin to tilt. This tilt makes the storm less symmetrical and usually weakens it. Irma experienced such conditions as it moved northwards from Cuba and onto Florida. But earlier, as it passed through the Caribbean, a low-shear environment and warm sea surface contributed to the high, sustained intensity.
In Irma’s case, forecasters used satellite, radar and aircraft reconnaissance data to monitor its position, intensity and size. The future track and intensity forecast relies heavily on computer model predictions from weather services around the world. But the forecasters don’t just use this computer data blindly – it is checked against, and synthesised with, the other data sources.
In Australia, government and industry investment in supercomputing and research is enabling the development of new tropical cyclone forecast systems that are more accurate. They provide earlier warning of tropical cyclone track and intensity, and even advance warning of their formation.
Still hard to predict destruction
Better forecasting helps us prepare for the different hazards presented by tropical cyclones.
The deadliest aspects of tropical cyclones are storm surges (when the sea rises and flows inland under the force of the wind and waves) and flooding from extreme rainfall, both of which pose a risk of drowning. Worldwide, all of the deadliest tropical cyclones on record featured several metres’ depth of storm surge, widespread freshwater flooding, or both.
Wind can severely damage buildings, but experience shows that even if the roof is torn off, well-constructed buildings still provide enough shelter for their occupants to have an excellent chance of surviving without major injury.
By and large, it is the water that kills. A good rule of thumb is to shelter from the wind, but flee from the water.
This means that predicting the damage and loss caused by a tropical cyclone is hard, because it depends on both the severity of the storm and the vulnerability of the area it hits.
Hurricane Katrina in 2005 provides a good illustration. Katrina was a Category 3 storm when it made landfall over New Orleans, about as intense at landfall as Australian tropical cyclones Vance, Larry and Yasi. Yet Katrina caused at least 1,200 deaths and more than $US100 billion in damage, making it the third deadliest and by far the most expensive storm in US history. One reason was Katrina’s relatively large area, which produced a very large storm surge. But the other factor was the extraordinary vulnerability of New Orleans, with much of the city below normal sea level and protected by levées that were buried or destroyed by the storm surge, leading to extensive deep flooding.
We have already seen with Hurricane Irma that higher sea levels have exacerbated the sea surge. Whatever happens in the remainder of Irma’s path, it will already be remembered as a spectacularly intense storm, and for its very significant impacts in the Caribbean and Florida. One can only imagine how much worse those impacts would have been had the populations not been forewarned.
But increased population and infrastructure in coastal areas and the effects of climate change means we in the weather forecast business must continue to improve. Forewarned is forearmed.