Cyclone Seroja just demolished parts of WA – and our warming world will bring more of the same


Bureau of Meteorology

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.




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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.

Emergency services crews in the WA town of Geraldton, preparing ahead of the arrival of Tropical Cyclone Seroja
Emergency services crews in the WA town of Geraldton, preparing ahead of the arrival of Tropical Cyclone Seroja – an event rarely seen this far south.
Department of Fire and Emergency Services WA

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.




Read more:
Wetlands have saved Australia $27 billion in storm damage over the past five decades


This article is part of Conversation series on the nexus between disaster, disadvantage and resilience. Read the rest of the stories here.The Conversation

Jonathan Nott, Professor of Physical Geography, James Cook University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Even after the rains, Australia’s environment scores a 3 out of 10. These regions are struggling the most


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Albert Van Dijk, Australian National University; Marta Yebra, Australian National University, and Shoshana Rapley, Australian National UniversityImproved weather conditions have pulled Australia’s environment out of its worst state on record, but recovery remains partial and precarious, new research reveals.

Each year, we collate a vast number of measurements on the state of our environment. The data are collected in many different ways – including satellites, field stations and surveys – then combined to produce an overall national score.

A year ago, after prolonged drought and devastating bushfires, Australia’s environment scored a shocking 0.8 out of ten. Our new research shows nature started its long road to recovery in 2020, especially in New South Wales and Victoria. Some of the regions with the poorest scores have high levels of social disadvantage, which risks being further entrenched by environmental disasters such as drought, bushfire and heatwaves.

Nationally, Australia’s environmental condition score increased by 2.6 points last year, to reach a (still very low) score of 3.2. But overall conditions across large swathes of the country remain poor.

Environmental Condition Score for 2020 by state and territory.
ANU Fenner School

Scores rising but still in the red

From a long list of environmental indicators we report on, seven are selected to calculate an overall score for each region, as well as nationally.

These indicators – high temperatures, river flows, wetlands, soil health, vegetation condition, growth conditions and tree cover – are chosen because they allow a comparison against previous years. See the graphic below to find the score for your region.

The largest improvements occurred in NSW and Victoria thanks to good rains. The poorest conditions occurred in the Northern Territory and Western Australia, where there was little solace from dry conditions.

Comparing local government areas, the best conditions occurred in Nillubik Shire on the northern edge of Melbourne. In contrast, the worst conditions occurred in Katherine in the Northern Territory and in the Shire of Ngaanyatjarraku in remote WA.



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From drought to rain

2020 started as badly as 2019 ended – with extreme temperatures, drought and fires, especially in Australia’s southeast. The Sydney suburb of Penrith was the hottest place on Earth on January 4 and, following the bushfires, Canberra had the most dangerous air quality in the world for several days. Clearly, climate change is already affecting our cities and nature.

By the end of summer, the high temperatures also caused another mass coral bleaching in the Great Barrier Reef – the third such event in five years.

Only in February-March did the weather turn, providing good and in some areas very plentiful rains – for example along the NSW coast. Later in the year officials declared an La Niña event – an ocean circulation pattern that normally encourages rainfall in Australia.

While rainfall was not extraordinarily high, it lifted most regions in eastern Australia out of extreme drought. Some parts of northern and western Australia missed out, however, and in some areas the drought deepened.

Taken as an average over the year and over the country, rainfall was 10% above the average for the previous two decades. The number of hot days – those reaching 35℃ – was 11% or nine days more than the 20-year average.

Values for 15 environmental indicators in 2020, expressed as the change from average 2000-2019 conditions. Similar to national economic indicators, they provide a summary but also hide regional variations, complex interactions and long-term context.
ANU Fenner School

The improved rainfall helped replenish dried soils, and national average soil moisture was close to average. Growth conditions for the NSW wheatbelt were the best in many years and tree cover increased in northern and eastern Australia.

The rain refilled many dams and reservoirs, especially in Canberra and Sydney. It also made some eastern rivers flow again, including the Darling River in NSW. But with such dry starting conditions, wetlands in inland eastern Australia filled only modestly and waterbird numbers remained low.

Drought persisted across large swathes of inland northern and western Australia, where in some parts, vegetation growth conditions were the worst in decades. And the surplus rain was often not enough to reach wetlands, which continued to shrink.




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New shoots in forest after fire
Signs of life: some parts of Australia have benefited from recent rain.
Shutterstock

Bushfires: few but locally severe

Fire activity in vast areas of inland Australia was very low, because a run of dry years did not leave much dry grass to burn.

Nationally, the total area burnt was 17 million hectares – 90% below the 20-year average. This led to 80 million tonnes of carbon emissions (43% below average).

Fire activity was not low everywhere. In southeast Australia, fires in southern NSW, East Gippsland and the ACT severely damaged forests and other ecosystems as well as people and property.

The full ecological damage of the Black Summer fires was not entirely apparent in 2020. That’s partly because COVID-19 restrictions made the situation difficult to assess.

The fires burned more than 80% of the habitat of 30 threatened species, and may have been the death blow for several. Food shortages and feral cats further reduced populations of surviving animals in the burnt ecosystems.

But some wildlife proved unexpectedly resilient. For example, a great effort by citizen scientists showed frogs rebounded well after the rains.

Another 15 species were added to the Threatened Species List in 2020. In good news, three species were removed from the list, including two species of tree frogs that recovered from the global chytrid fungus.




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Stopping the slow train wreck

The accelerating impacts of climate change will not stop here. New records will inevitably be broken. Heat, drought and fire will again damage our environment and lives. Some ecosystems will be lost forever. But even worse outcomes can be avoided – if the world can rein in greenhouse gas pollution.

There’s cause for cautious optimism. International pressure may force the Morrison government’s hand on climate action. Several states and territories have already taken decisive climate action. Low-emission energy and transport are advancing quickly. As individuals we can fly and drive less, get solar panels and divest from fossil fuel companies.

In the meantime, we must adapt to inevitable climate change and reduce other pressures on our ecosystems. Citizen scientists have proven essential in monitoring how individual species are faring – so download that app and enjoy nature even more. And plant a few trees to help nature along.

Finally, pressure your local, state and national politicians. Ask them: how are you addressing vegetation loss, invasive pests and over-extraction from rivers? If you don’t like the answer, tell them, or try to vote them out.

With greater urgency and some luck, there is still much to be salvaged.

The full report and a video summary are available here.




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This story is part of a series The Conversation is running on the nexus between disaster, disadvantage and resilience. You can read the rest of the stories here.The Conversation

Albert Van Dijk, Professor, Water and Landscape Dynamics, Fenner School of Environment & Society, Australian National University; Marta Yebra, Associate Professor in Environment and Engineering, Australian National University, and Shoshana Rapley, Research assistant, Australian National University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Climate explained: how particles ejected from the Sun affect Earth’s climate


Earth’s magnetic field protects us from the solar wind, guiding the solar particles to the polar regions.
SOHO (ESA & NASA)

Annika Seppälä


CC BY-ND

Climate Explained is a collaboration between The Conversation, Stuff and the New Zealand Science Media Centre to answer your questions about climate change.

If you have a question you’d like an expert to answer, please send it to climate.change@stuff.co.nz


When the Sun ejects solar particles into space, how does this affect the Earth and climate? Are clouds affected by these particles?

When we consider the Sun’s influence on Earth and our climate, we tend to think about solar radiation. We are acutely aware of the skin-burning dangers of ultraviolet, or UV, radiation.

But the Sun is an active star. It also continuously releases what is known as “solar wind”, made up of charged particles, largely protons and electrons, that travel at speeds of hundreds of kilometres per hour.

Some of these particles that reach Earth are guided into the polar atmosphere by our magnetic field. As a result, we can see the southern lights, aurora australis, in the southern hemisphere, and the northern equivalent, aurora borealis.

Aurora Australis
Aurora australis observed above southern New Zealand.
Shutterstock/Fotos593

This visible manifestation of solar particles entering Earth’s atmosphere is a constant reminder there is more to the Sun than sunlight. But the particles have other effects as well.




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Solar particles and ozone

When solar particles enter the atmosphere, their high energies ionise neutral atmospheric nitrogen and oxygen molecules, which make up 99% of the atmosphere. This “energetic particle precipitation”, named because it’s like a rain of particles from space, is a major source of ionisation in the polar atmosphere above 30km altitude — and it sets off a chain of reactions that produces chemicals that facilitate the destruction of ozone.

The impact of solar particles on atmospheric ozone was first observed in 1969. Since the early 2000s, thanks to new kinds of satellite observations, we have seen growing evidence that solar particles play an important part in influencing polar ozone. During particularly active times, when the Sun releases large amounts of particles into space, up to 60% of ozone at altitudes above 50km can be depleted. The effect can last for weeks.

Lower down in the atmosphere, below 50km, solar particles are important contributors to the year-to-year variability in polar ozone levels, often through indirect pathways. Here, solar particles again contribute to ozone loss, but a recent discovery showed they also help curb some of the depletion in the Antarctic ozone hole.

How ozone affects the climate

Most of the ozone in the atmosphere resides in a thin layer at altitudes of 20-25km — the “ozone layer”.

But ozone is everywhere in the atmosphere, from the Earth’s surface to altitudes above 100km. It is a greenhouse gas and plays a key role in heating and cooling the atmosphere, which makes it critical for climate.

In the southern hemisphere, changes in polar ozone are known to influence regional climate conditions.

Satellite image of Earth's atmosphere
Solar particles ionise nitrogen and oxygen molecules in the atmosphere, which leads to other chemical reactions that contribute to ozone destruction.
Shutterstock/PunyaFamily

Its depletion above Antarctica had a cooling effect, which in turn pulled the westerly wind jet that circles the continent closer. As the Antarctic hole recovers, this wind belt can meander further north and affect rainfall patterns, sea-surface temperatures and ocean currents. The Southern Annular Mode describes this north-south movement of the wind belt that circles the southern polar region.

Ozone is important for future climate predictions, not only in the thin ozone layer, but throughout the atmosphere. It is crucial we understand the factors that influence ozone variability, be it man-made or natural like the Sun.

The Sun’s direct influence

The link between solar particles and ozone is reasonably well established, but what about any direct effects solar particles may have on the climate?

We have observational evidence that solar activity influences regional climate variability at both poles. Climate models also suggest such polar effects link to larger climate patterns (such as the Northern and Southern Annular Modes) and influence conditions in mid-latitudes.

The details are not yet well understood, but for the first time the influence of solar particles on the climate system will be included in climate simulations used for the upcoming Intergovernmental Panel on Climate Change (IPCC) assessment.




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Solar weather has real, material effects on Earth


Through solar radiation and particles, the Sun provides a key energy input to our climate system. While these do vary with the Sun’s 11-year cycle of magnetic activity, they can not explain the recent rapid increase in global temperatures due to climate change.

We know rising levels of greenhouse gases in the atmosphere are pushing up Earth’s surface temperature (the physics have been known since the 1800s). We also know human activities have greatly increased greenhouse gases in the atmosphere. Together these two factors explain the observed rise in global temperatures.

What about clouds?

Clouds are much lower in the atmosphere than where most solar particles penetrate. Particles know as galactic cosmic rays (coming from the centre of our galaxy rather than the Sun) may be linked to cloud formation.

It has been suggested cosmic rays could influence the formation of condensation nuclei, which act as “seeds” for clouds. But recent research at the CERN nuclear research facility suggests the effects are insignificant.

This doesn’t rule out some other mechanisms for cosmic rays to affect cloud formation, but thus far there is little supporting evidence.The Conversation

Annika Seppälä, Senior Lecturer in Geophysics

This article is republished from The Conversation under a Creative Commons license. Read the original article.

What is a 1 in 100 year weather event? And why do they keep happening so often?


Andy Pitman, UNSW; Anna Ukkola, UNSW, and Seth WestraPeople living on the east coast of Australia have been experiencing a rare meteorological event. Record-breaking rainfall in some regions, and very heavy and sustained rainfall in others, has led to significant flooding.

In different places, this has been described as a one in 30, one in 50 or one in 100 year event. So, what does this mean?

What is a 1 in 100 year event?

First, let’s clear up a common misunderstanding about what a one in 100 year event means. It does not mean the event will occur exactly once every 100 years, or that it will not happen again for another 100 years.

For meteorologists, the one in 100 year event is an event of a size that will be equalled or exceeded on average once every 100 years. This means that over a period of 1,000 years you would expect the one in 100 year event would be equalled or exceeded ten times. But several of those ten times might happen within a few years of each other, and then none for a long time afterwards.




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Ideally, we would avoid using the phrase “one in 100 year event” because of this common misunderstanding, but the term is so widespread now it is hard to change. Another way to think about what a one in 100 year event means is that there is a 1% chance of an event of at least that size in any given year. (This is known as an “annual exceedance probability”.)

How common are 1 in 100 year events?

Many people are surprised by the feeling that one in 100 year events seem to happen much more often than they might expect. Although a 1% probability might sound pretty rare and unlikely, it is actually more common than you might think. There are two reasons for this.

First, for a given location (such as where you live), a one in 100 year event would be expected to occur on average once in 100 years. However, across all of Australia you would expect the one in 100 year event to be exceeded somewhere far more often than once in a century!

In much the same way, you might have a one in a million chance of winning the lottery, but the chance someone wins the lottery is obviously much higher.

Second, while a one in 100 year flood event might have a 1% chance of occurring in a given year (hence it’s referred to as a “1% flood”), the chance is much higher when looking at longer time periods. For example, if you have a house designed to withstand a 1% flood, this means over the course of 70 years there’s a roughly 50% chance the house would be flooded at some point during this time! Not the best odds.

How well do we know how often flood events occur?

Incidents like these 1% annual exceedance probability events are often referred to as “flood planning levels” or “design events”, because they are commonly used for a range of urban planning and engineering design applications. Yet this presupposes we can work out exactly what the 1% event is, which sounds simpler than it is in practice.

First of all, we use historical data to estimate the one in 100 year event, but Australia has only about 100 years of reliable meteorological observations, and even shorter records of river flow in most locations. We know for sure this 100-year record does not contain the largest possible events that could occur in terms of rainfall, drought, flood and so on. We have data from indirect paleoclimate evidence pointing to much larger events in the past.




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Sydney storm: are extreme rains and flash floods increasing?


So a 1% event is by no means a “worst case” scenario, and some of the evidence from paleoclimate data suggests the climate has been very different in the deep past.

Second, estimating the one in 100 year event using historical data assumes the underlying conditions are not changing. But in many parts of the world, we know rainfall and streamflow are changing, leading to a changing risk of flooding.

Moreover, even if there was no change in rainfall, changes to flood risk can occur due to a host of other factors. Increased flood risk can result from land clearing or other changes in the vegetation in a catchment, or changes in catchment management.

Increased occurrence of flooding can also be associated with poor planning decisions that locate settlements on floodplains. This means a one in 100 year event estimated from past observations could under- or indeed overestimate current flood risk.

A third culprit for influencing how often a flood occurs is climate change. Global warming is unquestionably heating the oceans and the atmosphere and intensifying the hydrological cycle. The atmosphere can hold more water in a warmer world, so we would expect to see rainfall intensities increasing.

Extreme rainfall events are becoming more extreme across parts of Australia. This is consistent with theory, which suggests we will see roughly a 7% increase in rainfall per degree of global warming.

Australia has warmed on average by almost 1.5℃, implying about 10% more intense rainfall. While 10% might not sound too dramatic, if a city or dam is designed to cope with 100mm of rain and it is hit with 110mm, it can be the difference between just lots of rain and a flooded house.

So what does this mean in practice?

Whether climate change “caused” the current extreme rainfall over coastal New South Wales is difficult to say. But it is clear that with temperatures and heavy rainfall events becoming more extreme with global warming, we are likely to experience one in 100 year events more often.

We should not assume the events currently unfolding will not happen again for another 100 years. It’s best to prepare for the possibility it will happen again very soon.




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The Conversation


Andy Pitman, Director of the ARC Centre of Excellence for Climate System Science, UNSW; Anna Ukkola, ARC DECRA Fellow, UNSW, and Seth Westra, Associate Professor, School of Civil, Environmental and Mining Engineering

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Wetlands have saved Australia $27 billion in storm damage over the past five decades



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Obadiah Mulder, University of Southern California and Ida Kubiszewski, Crawford School of Public Policy, Australian National University

Australia is in the midst of tropical cyclone season. As we write, a cyclone is forming off Western Australia’s Pilbara coast, and earlier in the week Queenslanders were bracing for a cyclone in the state’s far north (which thankfully, didn’t hit).

Australia has always experienced cyclones. But here and around the world, climate change means the cyclone threat is growing – and so too is the potential damage bill. Disadvantaged populations are often most at risk.

Our recent research shows 54 cyclones struck Australia in the 50 years between 1967 and 2016, causing about A$3 billion in damage. We found the damages would have totalled approximately A$30 billion, if not for coastal wetlands.

Wetlands such as mangroves, swamps, lakes and lagoons bear the brunt of much storm damage to coast, helping protect us and our infrastructure. But over the past 300 years, 85% of the world’s wetland area has been destroyed. It’s clear we must urgently preserve the precious little wetland area we have left.

A wetland close to coastal development.
Wetland areas provide important protection from cyclones.
Shutterstock

A critical buffer

National disasters cost Australia as much as A$18 billion each year on average. About one-quarter of this is due to cyclone damage.

Wetlands can mitigate cyclone and hurricane damage, by absorbing storm surges and slowing winds. For example in August 2020, Hurricane Laura hit the United States’ midwest. Massive damage was predicted, including a 6.5-metre storm surge extending 65 kilometres inland.

However the surge was one metre at most – largely because the storm drove straight into a massive wetland that absorbed most of the predicted flood.

In Australia, wetlands are lost through intentional infilling or drainage for mosquito control, or to create land for infrastructure and agriculture. They’re also lost due to pollution and upstream changes to water flows.

Caley Valley Wetlands,  next to Adani's Abbot Point coal terminal.
Australia’s wetlands are at risk. Pictured is the Caley Valley Wetlands, next to Adani’s Abbot Point coal terminal. Adani was fined for releasing polluted water into the wetland.
Gary Farr/ACF

Putting a price on cyclone protection

Our research set out to determine the financial value of the storm protection provided by Australia’s wetlands.

We examined the 54 cyclones that struck Australia in the five decades to 2016. We gathered data including:

  • physical damage wrought in each storm swath (or storm path)
  • gross domestic product (GDP) in the storm’s path
  • maximum windspeed during each storm, which helps predict damage
  • total area of wetlands in each swath.

Using a powerful type of statistics called Bayesian analysis, we estimated the extent to which GDP, windspeed and wetland area affected total damage. This allowed us to estimate damage caused in the absence of wetlands.

We found for every hectare of wetland, about A$4,200 per year in cyclone damage was avoided. This means the A$3 billion in cyclone damage over the past 50 years would have totalled approximately A$30 billion, if not for coastal wetlands.




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Importantly, the percentage of damage averted falls rapidly as wetland area decreases. And the protection afforded by a single hectare of wetland increases drastically if there are fewer other wetlands in the path of the storm. This makes protecting remaining wetland even more critical.

If the average cyclone path in Australia were to contain around 30,000 hectares of wetlands, it would avert about 90% of potential storm damage. If the wetland area dropped to 3,000 hectares, only about 30% of damage would be averted.

Climate change is making cyclones worse. By 2050, Australia’s annual damage bill could be as high as A$39 billion, assuming current levels of wetlands are maintained.

Seawalls and other artificial structures can be built along the coast to protect from storms. However, research in China has found wetlands are more cost-effective and efficient than man-made structures at preventing cyclone damage.

Unlike man-made structures, wetlands maintain themselves. Their only “cost” is the opportunity cost of not being able to use the land for something else.

People inspect cyclone damage
Wetlands can help prevent cyclone damage, such as this wrought in Queensland during Cyclone Debbie in 2017.
Dan Peled/AAP

Keeping wetlands safe

According to recent analysis by the authors, which is currently under peer review, global wetlands provide US$447 billion (A$657 billion) worth of protection from storms each year.

Of course, wetlands provide benefits beyond storm protection. They store carbon, regulate our climate and control flooding. They also absorb waste including pollutants and carbon, provide animal habitat and places for human recreation.

Wetlands are an incredibly important resource. It’s critical we protect them from development and keep them healthy, so they can continue to provide vital services.




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This story is part of a series The Conversation is running on the nexus between disaster, disadvantage and resilience. You can read the rest of the stories here.The Conversation

Obadiah Mulder, PhD Candidate in Computational Biology, University of Southern California and Ida Kubiszewski, Associate Professor, Crawford School of Public Policy, Australian National University

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Open data shows lightning, not arson, was the likely cause of most Victorian bushfires last summer



Tracy Nearmy/AAP

Dianne Cook, Monash University

As last summer’s horrific bushfires raged, so too did debate about what caused them. Despite the prolonged drought and ever worsening climate change, some people sought to blame the fires largely on arson.

Federal Coalition MPs were among those pushing the arsonist claim. And on Twitter, a fierce hashtag war broke out: “#ClimateEmergency” vs “#ArsonEmergency”.

Fire authorities rejected the arson claims, saying most fires were thought to be caused by lightning.

We dug into open data resources to learn more about the causes of last summer’s bushfires in Victoria, and further test the arson claim. Our analysis suggests 82% of the fires can be attributed to lightning, 14% to accidents and 1% to burning off. Only 4% can be attributed to arson.

Lightning in the sky
Lightning, not arson, caused most Victorian bushfires last summer.
Twitter

What we did

We started with hotspots data taken from the Himawari-8 satellite, which shows heat source locations over time and space, in almost real time. We omitted hotspots unlikely to be bushfires, and used a type of data mining called “spatiotemporal clustering” – where time dimension is introduced to geographic data – to estimate ignition time and location.

We supplemented this with data from other sources: temperature, moisture, rainfall, wind, sun exposure, fuel load, as well as distance to camp sites, roads and Country Fire Authority (CFA) stations.




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Victoria’s Department of Environment, Land, Water and Planning (DELWP) holds historical data on bushfire ignition from 2000 to the 2018-19 summer. The forensic research required to determine fire cause is laborious, and remotely sensed data from satellites may be useful and more immediate.

By training our model on the historical data, we can more immediately predict causes of last summer’s fires detected from satellite data. (Note: even though we were analysing events in the past, we use the term “predict” because authorities have not released official data.)

DELWP’s data attributes 41% of fires to lightning, 17% to arson, 34% to accidents and 7% to hazard reduction or back burning which escaped containment lines (which our analysis refers to as burning off).

Causes of fires from 2000-2019. Lightning is most common cause. The number of fires is increasing, and this is mostly due to accidents.
Own work

To make predictions for the 2019-20 bushfires, we needed an accurate model for causes in the historical data. We trained the model to predict one of four causes – lightning, accident, arson, burning off – using a machine learning algorithm.

The model performed well on the historical data: 75% overall accuracy, 90% accurate on lightning, 78% for accidents, and 54% for arson (which was mostly confused with accident, as would make sense).

The most important contributors to distinguishing between lightning and arson (or accident) ignition were distance to CFA stations, roads and camp sites, and average wind speed.

As might be expected, smaller distances to CFA stations, roads and camp sites, and higher than average winds, meant the fire was most likely the result of arson or accident. In the case of longer distances, where bush would have been largely inaccessible to the public, lightning was predicted to be the cause.

Spatial distribution of causes of fires from 2000-2019, and predictions for 2019-2020 season.
Own work

What we found

Our model predicted that 82% of Victoria’s fires in the summer of 2019-2020 were due to lightning. Most fires were located in densely vegetated areas inaccessible by road – similar to the historical locations. (The percentage is double that in the historical data, though, probably because the satellite hotspot data can see fire ignitions in locations inaccessible to fire experts).

All fires in February 2020 were predicted to be due to lightning. Accident and arson were commonly predicted causes in March, and early in the season. Reassuringly, ignition due to burning off was predicted primarily in October 2019, prior to the fire restrictions.

Spatio-temporal distribution of cause predictions for 2019-2020 season. Reassuringly, fires due to burning off primarily occurred in October, prior to fire restrictions. February fires were all predicted to be due to lightning.
Own work

Quicker fire ignition information

Our analysis used open-data and open-source software, and could be applied to fires elsewhere in Australia.

This analysis shows how we can quickly predict causes of bushfires, using satellite data combined with other information. It could reduce the work of fire forensics teams, and provide more complete fire ignition data in future.

The code used for the analysis can be found here. Explore the historical fire data, predictions for 2019-2020 fires, and a fire risk map for Victoria using this app.


This analysis is based on thesis research by Monash University Honours student Weihao Li. She was supervised by the author, and former Principal Inventive Scientist at AT&T Labs Research, Emily Dodwell. The Australian Centre of Excellence for Mathematical and Statistical Frontiers supported Emily’s travel to Australia to start this project. The full analysis is available here.

The Conversation

Dianne Cook, Professor of Business Analytics, Monash University

This article is republished from The Conversation under a Creative Commons license. Read the original article.