A wet winter, a soggy spring: what is the negative Indian Ocean Dipole, and why is it so important?

Nicky Wright, University of Sydney; Andréa S. Taschetto, UNSW, and Andrew King, The University of MelbourneThis month we’ve seen some crazy, devastating weather. Perth recorded its wettest July in decades, with 18 straight days of relentless rain. Overseas, parts of Europe and China have endured extensive flooding, with hundreds of lives lost and hundreds of thousands of people evacuated.

And last week, Australia’s Bureau of Meteorology officially declared there is a negative Indian Ocean Dipole — the first negative event in five years — known for bringing wet weather.

But what even is the Indian Ocean Dipole, and does it matter? Is it to blame for these events?

What is the Indian Ocean Dipole?

The Indian Ocean Dipole, or IOD, is a natural climate phenomenon that influences rainfall patterns around the Indian Ocean, including Australia. It’s brought about by the interactions between the currents along the sea surface and atmospheric circulation.

It can be thought of as the Indian Ocean’s cousin of the better known El Niño and La Niña in the Pacific. Essentially, for most of Australia, El Niño brings dry weather, while La Niña brings wet weather. The IOD has the same impact through its positive and negative phases, respectively.

Positive IODs are associated with an increased chance for dry weather in southern and southeast Australia. The devastating Black Summer bushfires in 2019–20 were linked to an extreme positive IOD, as well as human-caused climate change which exacerbated these conditions.

Negative IODs tend to be less frequent and not as strong as positive IOD events, but can still bring severe climate conditions, such as heavy rainfall and flooding, to parts of Australia.

The Indian Ocean Dipole (IOD) index, used to track the variability of the Indian Ocean Dipole. An event occurs after the index crosses the threshold for 8 weeks.
Bureau of Meteorology

The IOD is determined by the differences in sea surface temperature on either side of the Indian Ocean.

During a negative phase, waters in the eastern Indian Ocean (near Indonesia) are warmer than normal, and the western Indian Ocean (near Africa) are cooler than normal.

This causes more moisture-filled air to flow towards Australia, favouring wind pattern changes in a way that promotes more rainfall to southern parts of Australia. This includes parts of Western Australia, South Australia, Victoria, NSW and the ACT.

Generally, IOD events start in late autumn or winter, and can last until the end of spring — abruptly ending with the onset of the northern Australian monsoon.

The negative phase of the Indian Ocean Dipole.
Bureau of Meteorology

Why should we care?

We probably have a wet few months ahead of us.

The negative IOD means the southern regions of Australia are likely to have a wet winter and spring. Indeed, the seasonal outlook indicates above average rainfall for much of the country in the next three months.

In southern Australia, a negative IOD also means we’re more likely to get cooler daytime temperatures and warmer nights. But just because we’re more likely to have a wetter few months doesn’t mean we necessarily will — every negative IOD event is different.

Rainfall outlooks for August–October suggest that large parts of Australia will likely experience above-median rainfall.
Bureau of Meteorology, CC BY

While the prospect of even more rain might dampen some spirits, there are reasons to be happy about this.

First of all, winter rainfall is typically good for farmers growing crops such as grain, and previous negative IOD years have come with record-breaking crop production.

In fact, negative IOD events are so important for Australia that their absence for prolonged periods has been blamed for historical multi-year droughts in the past century over southeast Australia.

Negative IOD years can also bring better snow seasons for Australians. However, the warming trend from human-caused climate change means this signal isn’t as clear as it was in the past.

A negative IOD may mean a better snow season in the High Country.
Shutterstock

It’s not all good news

This is the first official negative IOD event since 2016, a year that saw one of the strongest negative IOD events on record. It resulted in Australia’s second wettest winter on record and flooding in parts of NSW, Victoria, and South Australia.

The 2016 event was also linked to devastating drought in East Africa on the other side of the Indian Ocean, and heavy rainfall in Indonesia.

Thankfully, current forecasts indicate the negative IOD will be a little milder this time, so we hopefully won’t see any devastating events.

The number of Indian Ocean Dipole events (per 30 years) based on climate models.
Modified from Abram et al. (2020)

Is the negative IOD behind the recent wet weather?

It’s too early to tell, but most likely not.

While Perth is experiencing one of its wettest Julys on record, the southwest WA region has historically been weakly influenced by negative IODs.

Negative IODs tend to be associated with moist air flow and lower atmospheric pressure further north and east than Perth, such as Geraldton to Port Hedland.

Outside of Australia, there has been extensive flooding in China and across Germany, Belgium, and The Netherlands.

It’s still early days and more research is needed, but these events look like they might be linked to the Northern Hemisphere’s atmospheric jet stream, rather than the negative IOD.

The jet stream is like a narrow river of strong winds high up in the atmosphere, formed when cool and hot air meet. Changes in this jet stream can lead to extreme weather.

What about climate change?

The IOD — as well as El Niño and La Niña — are natural climate phenomena, and have been occurring for thousands of years, before humans started burning fossil fuels. But that doesn’t mean climate change today isn’t having an effect on the IOD.

Scientific research is showing positive IODs — linked to drier conditions in eastern Australia — have become more common. And this is linked to human-caused climate change influencing ocean temperatures.

Climate models also suggest we may experience more positive IOD events in future, including increased chances of bushfires and drought in Australia, and fewer negative IOD events. This may mean we experience more droughts and less “drought-breaking” rains, but the jury’s still out.

When it comes to the recent, devastating floods overseas, scientists are still assessing how much of a role climate change played.

But in any case, we do know one thing for sure: rising global temperatures from climate change will cause more frequent and severe extreme events, including the short-duration heavy rainfalls associated with flooding, and heatwaves.

To avoid worse disasters in our future, we need to cut emissions drastically and urgently.

Nicky Wright, Research Fellow, University of Sydney; Andréa S. Taschetto, Associate Professor, UNSW, and Andrew King, ARC DECRA fellow, The University of Melbourne

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

You may have heard the ‘moon wobble’ will intensify coastal floods. Well, here’s what that means for Australia

Mark Gibbs, Australian Institute of Marine ScienceExtreme floods this month have been crippling cities worldwide. This week in China’s Henan province, a year’s worth of rain fell in just three days. Last week, catastrophic floods swept across western Germany and parts of Belgium. And at home, rain fell in Perth for 17 days straight, making it the city’s wettest July in 20 years.

But torrential rain isn’t the only cause of floods. Many coastal towns and cities in Australia would already be familiar with what are known as “nuisance” floods, which occur during some high tides.

A recent study from NASA and the University of Hawaii suggests even nuisance floods are set to get worse in the mid-2030s as the moon’s orbit begins another phase, combined with rising sea levels from climate change.

The study was conducted in the US. But what do its findings mean for the vast lengths of coastlines in Australia and the people who live there?

A triple whammy

We know average sea levels are rising from climate change, and we know small rises in average sea levels amplify flooding during storms. From the perspective of coastal communities, it’s not if a major flood will occur, it’s when the next one will arrive, and the next one after that.

But we know from historical and paleontological records of flooding events that in many, if not most, cases the coastal flooding we’ve directly experienced in our lifetimes are simply the entrée in terms of what will occur in future.

Flooding is especially severe when a storm coincides with a high tide. And this is where NASA and the University of Hawaii’s new research identified a further threat.

Researchers looked at the amplification phase of the natural 18.6-year cycle of the “wobble” in the moon’s orbit, first identified in 1728.

The orbit of the moon around the sun is not quite on a flat plane (planar); the actual orbit oscillates up and down a bit. Think of a spinning plate on a stick — the plate spins, but also wobbles up and down.

When the moon is at particular parts of its wobbling orbit, it pulls on the water in the oceans a bit more. This means for some years during the 18.6-year cycle, some high tides are higher than they would have otherwise been.

This results in increases to daily tidal rises, and this, in turn, will exacerbate coastal flooding, whether it be nuisance flooding in vulnerable areas, or magnified flooding during a storm.

View of Earth from the Moon — The moon’s orbit isn’t on a flat plane. It oscillates up and down, like a plate would when it spins on a stick.
Shutterstock

A major wobble amplification phase will occur in the mid-2030s, when climate change will make the problem become severe in some cases.

The triple whammy of the wobble in the moon’s orbit, ongoing upwards creep in sea levels from ocean warming, and more intense storms associated with climate change, will bring the impacts of sea-level rise earlier than previously expected — in many locations around the world. This includes in Australia.

So what will happen in Australia?

The locations in Australia where tides have the largest range, and will be most impacted by the wobble, aren’t close to the major population centres. Australia’s largest tides are close to Broad Sound, near Hay Point in central Queensland, and Derby in the Kimberley region of Western Australia.

However, many Australian cities host suburbs that routinely flood during larger high tides. Near my home in Meanjin (Brisbane), the ocean regularly backs up through the storm water drainage system during large high tides. At times, even getting from the front door to the street can be challenging.

Derby, WA, has one of the biggest tidal ranges in Australia.
Shutterstock

Some bayside suburbs in Melbourne are also already exposed to nuisance flooding. But a number of others that are not presently exposed may also become more vulnerable from the combined influence of the moon wobble and climate change — even when the weather is calm. High tide during this lunar phase, occurring during a major rainfall event, will result in even greater risk.

In high-income nations like Australia, sea-level rise means increasing unaffordability of insurance for coastal homes, followed by an inability to seek insurance cover at all and, ultimately, reductions in asset values for those unable or unwilling to adapt.

The prognosis for lower-income coastal communities that aren’t able to adapt to sea-level rise is clear: increasingly frequent and intense flooding will make many aspects of daily life difficult to sustain. In particular, movement around the community will be challenging, homes will often be inundated, unhealthy and untenable, and the provision of basic services problematic.

What do we do about it?

While our hearts and minds continue to be occupied by the pandemic, threats from climate change to our ongoing standard of living, or even future viability on this planet, haven’t slowed. We can pretend to ignore what is happening and what is increasingly unstoppable, or we can proactively manage the increasing threat.

Some coastal communities, such as in Melbourne’s bayside suburbs, may experience flooding, even if they never have before.
Shutterstock

Thankfully, approaches to adapting the built and natural environment to sea-level rise are increasingly being applied around the world. Many major cities have already embarked on major coastal adaptation programs – think London, New York, Rotterdam, and our own Gold Coast.

However, the uptake continues to lag behind the threat. And one of the big challenges is to incentivise coastal adaptation without overly impacting private property rights.

Perhaps the best approach to learning to live with water is led by the Netherlands. Rather than relocating entire communities or constructing large barriers like sea walls, this nation is finding ways to reduce the overall impact of flooding. This includes more resilient building design or reducing urban development in specific flood retention basins. This means flooding can occur without damaging infrastructure.

There are lessons here. Australia’s adaptation discussions have often focused on finding the least worst choice between constructing large seawalls or moving entire communities — neither of which are often palatable. This leads to inaction, as both options aren’t often politically acceptable.

The seas are inexorably creeping higher and higher. Once thought to be a problem for our grandchildren, it is becoming increasingly evident this is a challenge for the here and now. The recently released research confirms this conclusion.

Mark Gibbs, Principal Engineer: Reef Restoration, Australian Institute of Marine Science

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

Extreme Weather and Climate Change

The North American heatwave shows we need to know how climate change will change our weather

Christian Jakob, Monash University and Michael Reeder, Monash UniversityEight days ago, it rained over the western Pacific Ocean near Japan. There was nothing especially remarkable about this rain event, yet it made big waves twice.

First, it disturbed the atmosphere in just the right way to set off an undulation in the jet stream – a river of very strong winds in the upper atmosphere – that atmospheric scientists call a Rossby wave (or a planetary wave). Then the wave was guided eastwards by the jet stream towards North America.

Along the way the wave amplified, until it broke just like an ocean wave does when it approaches the shore. When the wave broke it created a region of high pressure that has remained stationary over the North American northwest for the past week.

This is where our innocuous rain event made waves again: the locked region of high pressure air set off one of the most extraordinary heatwaves we have ever seen, smashing temperature records in the Pacific Northwest of the United States and in Western Canada as far north as the Arctic. Lytton in British Columbia hit 49.6℃ this week before suffering a devastating wildfire.

What makes a heatwave?

While this heatwave has been extraordinary in many ways, its birth and evolution followed a well-known sequence of events that generate heatwaves.

Heatwaves occur when there is high air pressure at ground level. The high pressure is a result of air sinking through the atmosphere. As the air descends, the pressure increases, compressing the air and heating it up, just like in a bike pump.

Sinking air has a big warming effect: the temperature increases by 1 degree for every 100 metres the air is pushed downwards.

The North American heatwave has seen fires spread across the landscape.
NASA

High-pressure systems are an intrinsic part of an atmospheric Rossby wave, and they travel along with the wave. Heatwaves occur when the high-pressure systems stop moving and affect a particular region for a considerable time.

When this happens, the warming of the air by sinking alone can be further intensified by the ground heating the air – which is especially powerful if the ground was already dry. In the northwestern US and western Canada, heatwaves are compounded by the warming produced by air sinking after it crosses the Rocky Mountains.

How Rossby waves drive weather

This leaves two questions: what makes a high-pressure system, and why does it stop moving?

As we mentioned above, a high-pressure system is usually part of a specific type of wave in the atmosphere – a Rossby wave. These waves are very common, and they form when air is displaced north or south by mountains, other weather systems or large areas of rain.

Rossby waves are the main drivers of weather outside the tropics, including the changeable weather in the southern half of Australia. Occasionally, the waves grow so large that they overturn on themselves and break. The breaking of the waves is intimately involved in making them stationary.

Importantly, just as for the recent event, the seeds for the Rossby waves that trigger heatwaves are located several thousands of kilometres to the west of their location. So for northwestern America, that’s the western Pacific. Australian heatwaves are typically triggered by events in the Atlantic to the west of Africa.

Another important feature of heatwaves is that they are often accompanied by high rainfall closer to the Equator. When southeast Australia experiences heatwaves, northern Australia often experiences rain. These rain events are not just side effects, but they actively enhance and prolong heatwaves.

What will climate change mean for heatwaves?

Understanding the mechanics of what causes heatwaves is very important if we want to know how they might change as the planet gets hotter.

We know increased carbon dioxide in the atmosphere is increasing Earth’s average surface temperature. However, while this average warming is the background for heatwaves, the extremely high temperatures are produced by the movements of the atmosphere we talked about earlier.

So to know how heatwaves will change as our planet warms, we need to know how the changing climate affects the weather events that produce them. This is a much more difficult question than knowing the change in global average temperature.

How will events that seed Rossby waves change? How will the jet streams change? Will more waves get big enough to break? Will high-pressure systems stay in one place for longer? Will the associated rainfall become more intense, and how might that affect the heatwaves themselves?

From climate change to weather change

There is one thing we do know for sure: we need to up our game in understanding how the weather is changing as our planet warms, because weather is what has the biggest impact on humans and natural systems.

To do this, we will need to build computer models of the world’s climate that explicitly include some of the fine detail of weather. (By fine detail, we mean anything about a kilometre in size.) This in turn will require investment in huge amounts of computing power for tools such as our national climate model, the Australian Community Climate and Earth System Simulator (ACCESS), and the computing and modelling infrastructure projects of the National Collaborative Research Infrastructure Strategy (NCRIS) that support it.

We will also need to break down the artificial boundaries between weather and climate which exist in our research, our education and our public conversation.

Christian Jakob, Professor in Atmospheric Science, Monash University and Michael Reeder, Professor, School of Earth, Atmosphere and Environment, Monash University

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

Three weeks without electricity? That’s the reality facing thousands of Victorians, and it will happen again

Anthony Richardson, RMIT UniversityLast week’s storm system wreaked havoc across Victoria. Some 220,000 households and businesses lost power, and residents in the hills on Melbourne’s fringe were warned yesterday it might not be restored for three weeks.

The extreme weather severely damaged the poles and powerlines that distribute electricity, particularly in the Mount Dandenong area. Senior AusNet official Steven Neave said of the region this week, “we basically have no network left, the overhead infrastructure is pretty much gone. It requires a complete rebuild”.

That leaves about 3,000 customers without electricity for weeks, in the heart of winter. The loss of power also cut mobile phone and internet services and reportedly allowed untreated water to enter drinking supplies.

So, could this disaster have been avoided? And under climate change, how can we prepare for more events like this?

fallen tree on powerlines — Fallen trees brought down power lines across Melbourne.
Daniel Pockett/AAP

An uncertain future

The Mount Dandenong area is heavily forested, and the chance of above-ground power infrastructure being hit by falling trees is obviously high.

Without electricity, people cannot turn on lights, refrigerate food or medications, cook on electric stoves or use electric heaters. Electronic banking, schooling and business activities are also badly disrupted. For vulnerable residents, in particular, the implications are profound.

Such disruptions are hard to avoid, at least while the electricity network is above ground. Good management, however, can prevent some trees coming down in storms.

The more pertinent question is: how can we prepare for such an event in the future?

Scientists warn such extreme weather will increase in both frequency and severity as climate change accelerates. The Australian Energy Market Operator is acutely aware of this, warning climate change poses “material risks to individual assets, the integrated energy system, and society”.

However, it’s challenging to predict exactly how future heatwaves, storms, bushfires and floods will affect the power network. As AEMO notes, many climate models related to storms and cyclones involve an element of unpredictability. So, plans to make the electricity system more resilient must address this uncertainty.

As researchers have noted, there is no “one future” to prepare for – we must be ready for many potential eventualities.

tree fallen on house — Under climate change, extreme weather is predicted to become more severe.
Daniel Pockett/AAP

Yallourn – the bigger problem?

Meanwhile, in Victoria’s LaTrobe Valley, a situation at the Yallourn coal-fired power station which may have even greater consequences for electricity supplies.

A coal mine wall adjacent to the station is at risk of collapse after flooding in the Morwell River caused it to crack. If the wall is breached and the mine is flooded, as happened in 2012, there will be no coal to power the station and almost a quarter of Victoria’s power supply could be out for months.

Victoria’s energy needs are increasingly supplied by renewables. However, losing Yallourn’s generation capacity would reduce the capacity of the network to adapt to other possible disruptions.

If further disruptions seem unlikely, it’s worth noting the Callide Power Station in Queensland is still operating at reduced capacity after a recent fire.

power plant with chimneys — A wall adjacent to the Yallourn power plant may collapse.
Julian Smith/AAP

Look beyond the immediate crisis

The Victorian government has offered up to A$1,680 per week, for up to three weeks, to help families without power buy supplies and find alternative accommodation.

Welfare groups say the assistance could be improved. They have called for changes to make it quicker and easier for people to access money, cash injections to frontline charities and more temporary accommodation facilities for displaced people and their pets.

While no doubt needed, these are all reactive responses targeted at those without electricity. When any system is disrupted, however, the effects can be widespread and felt long after the initial problem has been addressed.

Take dairy farmers in Gippsland, for example, who could not milk their cows without electricity. Cows must be milked regularly or else they stop producing milk – they cannot be “switched back on” when electricity is restored. Longer-term assistance may well be required for farmers facing such ripple effects.

And as welfare groups have noted, power companies should support affected customers over the long-term, with electricity discounts, deferrals and payment plans.

Sign reading 'power and shower' — Relief centres offer affected residents a hot shower and electricity access, but longer-term solutions are also needed.
Daniel Pockett/AAP

A call for backup

So, what else can be done to prepare for future power disruptions? Those with backup options, such as portable fuel-powered generators, or off-grid household batteries connected to solar panels, will undoubtedly be more resilient in such events.

These are examples of “system redundancy”, providing alternative electricity until the network is restored.

But it costs money to invest in household batteries or a generator that may never be used. Resilience is often a function of wealth, and the less well-off risk being left behind.

Certainly, governments can act to make society as a whole more resilient to power outages. For example, mobile phone towers have backup battery life of just 24 hours. As Victoria’s Emergency Management Commissioner Andrew Crisp said this week, extending that is something authorities “need to look at”.

Power and communications infrastructure could be moved underground to protect it from storms. While such a move would be expensive, it has been argued not doing so will lead to greater long-term costs under a changing climate.

The recent challenges at Yallourn and Callide show the risks inherent in a centralised electricity network dominated by coal.

Certainly, integrating renewable energy sources into the power network comes with its own challenges. However, expanding energy storage such as batteries, or shifting to small, community-level microgrids will go a long way to improving the resilience of the system.

This story is part of a series The Conversation is running on the nexus between disaster, disadvantage and resilience. It is supported by a philanthropic grant from the Paul Ramsay Foundation. Find the series here.

Anthony Richardson, Researcher and Teacher, Centre for Urban Research, RMIT University

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

How rain, wind, heat and other heavy weather can affect your internet connection

James Jin Kang, Edith Cowan University and Paul Haskell-Dowland, Edith Cowan UniversityWhen your Netflix stream drops out in the middle of a rainstorm, can you blame the wild weather?

Quite possibly. The weather can affect the performance of your internet connection in a variety of ways.

This can include issues such as physical damage to the network, water getting into electrical connections, and wireless signal interference. Some types of connection are more vulnerable to weather than others.

The behaviour of other humans in response to the weather can also have an effect on your connection.

How rain can affect your internet connection

Internet connections are much more complicated than the router and cables in our homes. There are many networking devices and cables and connections (of a variety of types and ages) between our homes and the websites we are browsing.

How do we connect to the Internet?

An internet connection may involve different kinds of physical link, including the copper wiring used in the old phone network and more modern fibre optic connections. There may also be wireless connections involved, such as WiFi, microwave and satellite radio.

Example of multi-layered internet access.
Ferran, CC BY-SA 4.0 https://creativecommons.org/licenses/by-sa/4.0, via Wikimedia Commons

Rain can cause physical damage to cables, particularly where telecommunication networks are using old infrastructure.

ADSL-style connections, which use the old phone network, are particularly vulnerable to this type of interference. Although many Australians may be connected to the National Broadband Network (NBN), this can still run (in part) through pre-existing copper wires (in the case of “fibre to the node” or “fibre to the cabinet” connections) rather than modern optical fibres (“fibre to the home”).

Different types of NBN connection.
Riick, CC BY-SA 3.0 http://creativecommons.org/licenses/by-sa/3.0/, via Wikimedia Commons

Much of the internet’s cabling is underground, so if there is flooding, moisture can get into the cables or their connectors. This can significantly interfere with signals or even block them entirely, by reducing the bandwidth or causing an electrical short-circuit.

But it isn’t just your home connection that can be impacted. Wireless signals outside the home or building can be affected by rainfall as water droplets can partially absorb the signal, which may result in a lower level of coverage.

Even once the rain stops, the effects can still be felt. High humidity can continue to affect the strength of wireless signals and may cause slower connection speeds.

Copper cables and changed behaviour

If you are using ADSL or NBN for your internet connection, it is likely copper phone cables are used for at least some of the journey. These cables were designed to carry voice signals rather than data, and on average they are now more than 35 years old.

Only around 18% of Australian homes have the faster and more reliable optical-fibre connections.

There is also a behaviour factor. When it rains, more people might decide to stay indoors or work from home. This inevitably leads to an increase in the network usage. When a large number of people increase their internet usage, the limited bandwidth available is rapidly consumed, resulting in apparent slowdowns.

This is not only within your home, but is also aggregated further up the network as your traffic is joined by that from other homes and eventually entire cities and countries.

Heatwaves and high winds

In Australia, extreme cold is not usually a great concern. Heat is perhaps a more common problem. Our networking devices are likely to perform more slowly when exposed to extreme heat. Even cables can suffer physical damage that may affect the connection.

Imagine your computer fan is not running and the device overheats — it will eventually fail. While the device itself may be fine, it is likely the power supply will struggle in extremes. This same issue can affect the networking equipment that controls our internet connection.

Satellite internet services for rural users can be susceptible to extreme weather, as the satellite signals have to travel long distances in the air.

Radio signals are not usually affected by wind, but hardware such as satellite dishes can be swayed, vibrated, flexed or moved by the wind.

Most of the time, human behaviour is the main cause

For most users, the impact of rain will be slight – unless they are physically affected by a significant issue such as submerged cables, or they are trying to use WiFi outside during a storm.

So, can weather affect your internet connection? Absolutely.

Will most users be affected? Unlikely.

So if your favourite Netflix show is running slow during in rainy weather, it’s most likely that the behaviour of other humans is to blame — holed up indoors and hitting the internet, just like you.

James Jin Kang, Lecturer, Computing and Security, Edith Cowan University and Paul Haskell-Dowland, Associate Dean (Computing and Security), Edith Cowan University

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

Freakish Natural Disasters

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

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.

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.

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

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

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.

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.

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.

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.

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.

After the floods, stand by for spiders, slugs and millipedes – but think twice before reaching for the bug spray

Caitlyn Forster, University of Sydney; Dieter Hochuli, University of Sydney, and Eliza Middleton, University of SydneyRecord-breaking rain has destroyed properties across New South Wales, forcing thousands of people to evacuate and leaving hundreds homeless.

Humans aren’t the only ones in trouble. Many of the animals that live with and around us are also heading for higher ground as the floodwaters rise.

Often small creatures — especially invertebrates like spiders, cockroaches and millipedes — will seek refuge in the relatively dry and safe environments of people’s houses. While this can be a problem for the human inhabitants of the house, it’s important to make sure we don’t add to the ecological impact of the flood with an overzealous response to these uninvited guests.

Warragamba Dam in southwestern Sydney has been spilling a Sydney Harbour’s worth of water each day during the rains.
Eliza Middleton, Author provided

What floods do to ecosystems

Floods can have a huge impact on ecosystems, triggering landslides, increasing erosion, and introducing pollutants and soil into waterways. One immediate effect is to force burrowing animals out of their homes, as they retreat to safer and drier locations. Insects and other invertebrates living in grass or leaf litter around our homes are also displaced.

Burrowing invertebrates come to the surface during floods, providing food for opportunistic birds.
Dieter Hochuli, Author provided

Snakes have reportedly been “invading” homes in the wake of the current floods. Spiders too have fled the rising waters. Heavy rain can flood the burrows of the Australian funnelweb, one of the world’s most venomous spiders.

Some invertebrates will boom; others may plummet

Rain increases greenery, which can support breeding booms of animals such as mosquitoes, locusts, and snails.

Even species that don’t thrive after floods are likely to become more visible as they flock to our houses for refuge. But an apparent short-term increase in numbers may conceal a longer story of decline.

After periods of flooding, the abundance of invertebrates can fall by more than 90% and the number of different species in an area significantly drops. This has important implications for the recovery of an ecosystem, as many of the ground dwelling invertebrates displaced by floods are needed for soil cycling and decomposition.

So before you reach for the bug spray, consider the important role these animals play in our ecosystem.

What to do with the extra house guests?

If your house has been flooded, uninvited creatures taking shelter in your house are probably one of the smaller issues you are facing.

Once the rain subsides, cleaning in and around your property will help reduce unwanted visitors. Inside your house, you may see an increase in cockroaches, which flourish in humid environments. Ventilating the house to dry out any wet surfaces can help get rid of cockroach infestations, and filling crevices can also deter unwanted visitors.

In the garden, you may see an increase in flies in the coming weeks and months as they lay eggs in rotting plants. Consider removing any fruit and vegetables in the garden that may rot.

Mosquitoes are also one to watch as they lay eggs in standing water. Some species pose a risk of diseases such as Ross River virus. To prevent unwanted mozzies, make sure to empty things that have filled with rainwater, such as buckets and birdbaths.

If you do encounter one of our more dangerous animals in your home, such as venomous snakes and spiders, do not handle them yourself. If you find an injured or distressed snake, or are concerned about snakes in your house, call your local wildlife group who will be able to relocate them for you.

Just like the floods, which will subside as the water moves on, the uninvited gathering of animals is a temporary event. Most visitors will quickly disperse back to more appropriate habitat when the weather dries, and their usual homes are available again.

You may see an increase in slugs in your local area after rainy conditions.
Eliza Middleton @smiley_lize

Don’t sweat the small stuff

While many of the impacts of floods are our own making, through poor planning and development in flood-prone areas, effective design of cities and backyards can mitigate the risks of floods. Vegetation acts as a “sponge” for stormwater, and appropriate drainage allows water to flow through more effectively. Increasing backyard vegetation also provides extra habitat for important invertebrate species, including pollinators and decomposers.

With severe weather events on the rise, it is important to understand how ecosystems respond to, and recover from natural disasters. If invertebrates are unable to perform vital ecosystem functions, such as soil cycling, decomposition, and pollination, ecosystems may struggle to return to their pre-flood state. If the ecosystems don’t recover, we may see prolonged booms of nuisance pests such as mosquitoes.

A few temporary visitors are are a minor inconvenience in comparison to the impacts floods have on the environment, infrastructure and the health and well-being of people impacted. So while it may seem like a bit of a creepy inconvenience, maybe we should let our house guests stay until the flood waters go down.

Caitlyn Forster, PhD Candidate, School of Life and Environmental Sciences, University of Sydney; Dieter Hochuli, Professor, School of Life and Environmental Sciences, University of Sydney, and Eliza Middleton, Laboratory Manager, School of Life and Environmental Sciences, University of Sydney

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

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