Native forest logging makes bushfires worse – and to say otherwise ignores the facts


Philip Zylstra, University of Wollongong; Grant Wardell-Johnson, Curtin University; James Watson, The University of Queensland, and Michelle Ward, The University of QueenslandThe Black Summer bushfires burned far more temperate forest than any other fire season recorded in Australia. The disaster was clearly a climate change event; however, other human activities also had consequences.

Taking timber from forests dramatically changes their structure, making them more vulnerable to bushfires. And, crucially for the Black Summer bushfires, logged forests are more likely to burn out of control.

Naturally, the drivers of the fires were widely debated during and after the disaster. Research published earlier this month, for example, claimed native forest logging did not make the fires worse.

We believe these findings are too narrowly focused and in fact, misleading. They overlook a vast body of evidence that crown fire – the most extreme type of bushfire behaviour, in which tree canopies burn – is more likely in logged native forests.

Logged forest
The authors say logging increases the risk of intense crown fires.
Australian National University

Crown fires vs scorch

The Black Summer fires occurred in the 2019-20 bushfire season and burned vast swathes of Australia’s southeast. In some cases, fire spread through forests with no recorded fire, including some of the last remnants of ancient Gondwanan rainforests.

Tragically, the fires directly killed 33 people, while an estimated 417 died due to the effects of smoke inhalation. A possible three billion vertebrate animals perished and the risk of species extinctions dramatically increased.

Much of the forest that burned during Black Summer experienced crown fires. These fires burn through the canopies of trees, as well as the undergrowth. They are the most extreme form of fire behaviour and are virtually impossible to control.

Crown fires pulse with such intense heat they can form thunderstorms which generate lightning and destructive winds. This sends burning bark streamers tens of kilometres ahead of the fire, spreading it further. The Black Summer bushfires included at least 18 such storms.

Various forest industry reports have recognised logging makes bushfires harder to control.

And to our knowledge, every empirical analysis so far shows logging eucalypt forests makes them far more likely to experience crown fire. The studies include:

  • A 2009 paper suggesting changes in forest structure and moisture make severe fire more likely in logging regrowth compared to undisturbed forest
  • 2012 research concluding the probability of crown fires was higher in recently logged areas than in areas logged decades before
  • A 2013 study that showed the likelihood of crown fire halved as forests aged after a certain point
  • 2014 findings that crown fire in the Black Saturday fires likely peaked in regrowth and fell in mature forests
  • 2018 research into the 2003 Australian Alps fires, which found the same increase in the likelihood of crown fire during regrowth as was measured following logging.

The findings of these studies are represented in the image below. The lines a, b and c refer to the 2013, 2014 and 2018 studies respectively.

Graph showing the likelihood of crown fire relative to years since logging or fire

Author supplied

Crown fires take lives

The presence of crown fire is a key consideration in fire supression, because crown fires are very hard to control.

However, the study released last week – which argued that logging did not worsen the Black Summer fires – focused on crown “scorch”. Crown scorch is very different to crown fire. It is not a measure of how difficult it is to contain the fire, because even quite small flames can scorch a drought-stressed canopy.

Forestry studies tend to focus more on crown scorch, which damages timber and is far more common than crown fires.

But the question of whether logging made crown scorch worse is not relevant to whether a fire was uncontrollable, and thus was able to destroy homes and lives.

Importantly, when the study said logging had a very small influence on scorch, this was referring to the average scorch over the whole fire area, not just places that had been logged. That’s like asking how a drought in the small town of Mudgee affects the national rainfall total: it may not play a large role overall, but it’s pretty important to Mudgee.

The study examined trees in previously logged areas, or areas that had been logged and burned by fires of any source. It found they were as likely to scorch on the mildest bushfire days as trees in undisturbed forests on bad days. These results simply add to the body of evidence that logging increases fire damage.




Read more:
I’m searching firegrounds for surviving Kangaroo Island Micro-trapdoor spiders. 6 months on, I’m yet to find any


Timber plantation after fire
Forestry industry studies tend to focus on crown scorch.
Richard Wainwright/AAP

Managing forests for all

Research shows forests became dramatically less likely to burn when they mature after a few decades. Mature forests are also less likely to carry fire into the tree tops.

For example during the Black Saturday fires in 2009, the Kilmore East fire north of Melbourne consumed all before it as a crown fire. Then it reached the old, unlogged mountain ash forests on Mount Disappointment and dropped to the ground, spreading as a slow surface fire.

The trees were scorched. But they were too tall to ignite, and instead blocked the high winds and slowed the fire down. Meanwhile, logged ash forests drove flames high into the canopy.

Despite decades of opportunity to show otherwise, the only story for eucalypt forests remains this: logging increases the impact of bushfires. This fact should inform forest management decisions on how to reduce future fire risk.

We need timber, but it must be produced in ways that don’t endanger human lives or the environment.




Read more:
‘We know our community better than they do’: why local knowledge is key to disaster recovery in Gippsland


The Conversation


Philip Zylstra, Adjunct Associate Professor at Curtin University, Honorary Fellow at University of Wollongong, University of Wollongong; Grant Wardell-Johnson, Associate Professor, Environmental Biology, Curtin University; James Watson, Professor, The University of Queensland, and Michelle Ward, PhD Candidate, The University of Queensland

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

New research finds native forest logging did not worsen the Black Summer bushfires


Shutterstock

David Bowman, University of TasmaniaThe Black Summer bushfires shocked the world and generated enormous global media interest. Fire scientists like myself found themselves filling a role not unlike sport commentators, explaining the unfolding drama in real time.

Scientists who engaged with the media during the crisis straddled two competing imperatives. First was their duty to share their knowledge with the community while knowing their understanding is imperfect. Second was the ethical obligation to rigorously test hypotheses against data analysis and peer review – the results of which could only be known long after the fires were out.

One area where this tension emerged was around the influential idea that logging exacerbated the bushfire disaster. During the fire crisis and in the months afterwards, some scientists suggested logging profoundly affected the fires’ severity and frequency. There were associated calls to cease native forestry and shift wood production to plantations.

But there is no scientific consensus about the possible effects of logging on fire risk. In fact, research by myself and colleagues, published in Nature Ecology and Evolution today, shows logging had little if any effect on the Black Summer bushfires. Rather, the disaster’s huge extent and severity were more likely due to unprecedented drought and sustained hot, windy weather.

These findings are significant for several reasons. Getting to the bottom of the bushfires’ cause is essential for sustainable forest management. And, more importantly, our research confirms the devastating role climate change played in the Black Summer fires.

Firefighters recover after battling blazes at Kangaroo Island on 10 January 2019.
David Mariuz/AAP

Looking for patterns

Our research focused on 7 million hectares of mostly eucalyptus forests, from the subtropics to temperate zones, which burned between August 2019 and March 2020.

There is some evidence to suggest logged areas are more flammable that unlogged forests. Proponents of this view say logging regimes make the remaining forests hotter and drier, and leave debris on the ground that increases the fuel load.

In our research, we wanted to determine:

  • the relative roles logging and other factors such as climate played in fires that destroyed or completely scorched forest canopies
  • whether plantations are more vulnerable to canopy scorch than native forests.

To do so, we used landscape ecology techniques that could compare very large areas with different patterns of land use and fire severity. We sampled 32% of the area burnt in three regions spanning the geographic range of the fires.




Read more:
The government has pledged over $800m to fight natural disasters. It could be revolutionary — if done right


firefighters run past fire
The research used landscape ecology techniques to compare large areas.
Shutterstock

What we found

Fire intensity is classified according to the vertical layer of vegetation burnt. A scorched tree canopy suggests the most intense type of fire, where the heat extended from the ground to the treetops.

We found several predictors of canopy damage. First, completely scorched canopy, or canopy consumed by fire, typically occurred across connected swathes of bushland. This most likely reflected instances where the fire made a “run”, driven by localised winds.

Extreme weather fire conditions were the next most important predictor of canopy damage. The drought had created vast areas of tinder-dry forests. Temperatures during the fire season were hot and westerly winds were strong.

Southeast Australia’s climate has changed, making such extreme fire weather more frequent, prolonged and severe.

Logging activity in the last 25 years consistently ranked “low” as a driver of fire severity. This makes sense for several reasons.

As noted above, fire conditions were extraordinarily extreme. And there was mismatch between the massive area burnt and the comparatively small areas commercially logged in the last 25 years (4.5% in eastern Victoria, 5.3% in southern NSW and 7.8% in northern NSW).

Fire severity is also related to landscape features: fire on ridges is generally worse than in sheltered valleys.

Our research also found timber plantations were as prone to severe fire as native forestry areas. In NSW (the worst-affected state) one-quarter of plantations burned – than 70% severely. This counteracts the suggestion using plantations, rather than logging native forest, can avoid purported fire hazards.




Read more:
Australia, you have unfinished business. It’s time to let our ‘fire people’ care for this land


plantation forest divided by road
Plantation forests were found to be highly flammable.
Shutterstock

A challenge awaits

Our findings are deeply concerning. They signal there is no quick fix to the ongoing fire crisis afflicting Australia and other flammable landscapes.

The crisis is being driven by relentless climate change. Terrifyingly, it has the potential to turn forests from critical stores of carbon into volatile sources of carbon emissions released when vegetation burns.

Under a rapidly warming and drying climate, fuel loads are likely to become less important in determining fire extent and severity. This will make it increasingly difficult, if not impossible, to lower fuel loads in a way that will limit bushfire severity.

A massive challenge awaits. We must find socially and environmentally acceptable ways to make forests more resilient to fire while the also produce sustainable timber products, store carbon, provide water and protect biodiversity.

The next step is a real-world evaluation of management options. One idea worth exploring is whether the fire resistance of native forests can be improved in specific areas by altering tree density, vegetation structure or fuel loads, while sustaining biodiversity and amenity.

Commercial forestry could potentially do this, with significant innovation and willingness to let go of current practices.

Through collective effort, I’m confident we can sustainably manage of forests and fire. Our study is but a small step in a much bigger, zig-zagging journey of discovery.




Read more:
As bushfire and holiday seasons converge, it may be time to say goodbye to the typical Australian summer holiday


The Conversation


forest regenerating after fire
Forests must become fire-resilient while performing other functions.
Shutterstock

David Bowman, Professor of Pyrogeography and Fire Science, University of Tasmania

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

The government has pledged over $800m to fight natural disasters. It could be revolutionary — if done right


Shutterstock

Paul Barnes, UNSWTo help Australia adapt to climate change and manage the disasters that come with it, the federal government this week pledged A$600 million towards establishing the National Recovery and Resilience Agency, and $210 million for the Australian Climate Service initiative.

The sizeable investments make sense, as Australia’s threat landscape has changed. Climate change, drought, land clearing, urban growth and other activities have significantly increased the chances of natural hazards and disasters Australia-wide. All of which are costly to recover from.

The new organisations could deliver revolutionary benefits to Australia by better aligning policy and practice in a more agile way that matches the complex set of threats we face.

There are, however, issues that warrant attention. It’s not yet clear how the government plans to bring together Australia’s best experts — including policy thinkers, emergency managers, researchers and practitioners — to address the complex, evolving threats. Currently, it seems the role of universities has not been adequately defined.

Australia’s recent disasters

The 2019-20 bushfire season was arguably the most extreme in living memory. It started earlier than what might normally have been expected and made history for its severity and widespread damage to life, property and the environment.

Bushfires weren’t the only natural hazard Australia dealt with during this period. Insurance claims from hailstorms, flooding and bushfire damage for the 2019-20 period exceeded $5.19 billion.

A man and woman use a kayak to travel up a flooded street.
The March floods in western Sydney peaked at a staggering 12.9 metres.
Shutterstock

Then came the severe flooding across New South Wales in March, which peaked at 12.9 metres. As of March 23, policyholders had lodged up to 11,700 insurance claims associated with these storms.




Read more:
The world endured 2 extra heatwave days per decade since 1950 – but the worst is yet to come


While these recent disasters were unprecedented in their scale and impact, we can expect disasters in the future to worsen due to climate change, from longer heatwaves to intensifying cyclones and a range of cascading and cumulative impacts on society.

This is why the federal government’s announcement this week is extremely important.

So what will these initiatives do?

The new organisations are in response to recommendations from the recent bushfire royal commission, and as part of next week’s federal budget.

The National Recovery and Resilience Agency will be led by former Northern Territory chief minister Shane Stone, and brings together the responsibilities of the national agencies in charge of flood and bushfire recovery.

Its job is to oversee $600 million that will go towards new programs for disaster preparation and mitigation. It’ll focus on minimising disruptive impacts on communities and assist in making them ready to face future disasters. It will also administer the $2 billion National Bushfire Recovery Fund on an ongoing basis.




Read more:
Sydney’s disastrous flood wasn’t unprecedented: we’re about to enter a 50-year period of frequent, major floods


A key enabler of this is the National Climate Resilience and Adaptation Strategy, which is currently getting updated after its first release in 2015. The new strategy will be released later this year, and should be vital in underpinning the direction of the new agency.

The government must ensure the strategy provides guidance that matches the goals of the new agency – in particular that of building resilience. It’s important to recognise that while disaster response is generally similar across the board, the effects of disasters vary depending on the community, urban and physical features, as well as socioeconomic levels and access to services.

And the Australian Climate Service initiative will, according to Environment Minister Sussan Ley:

help provide an environmental road map in our planning for infrastructure, housing and basic services like power, telecommunications, and water [and in] anticipating and adapting to the impacts of [a] changing climate.

Together, the benefits of both new organisations have the potential to be revolutionary.

They — along with a new national research centre focused on hazard resilience and disaster risk reduction (announced in July last year) — may be the largest realignments in disaster management policy and practice for a generation.

But how they’re implemented and coordinated will, ultimately, determine this.

There’s more to do

A potential issue with the Australian Climate Service Initiative that might limit its effectiveness is its emphasis on the roles of the Bureau of Meteorology, CSIRO, the Australian Bureau of Statistics and Geoscience Australia.

This collaboration means the initiative has access to huge amounts of data, information resources, and links to the National Environmental Science Program and Great Barrier Reef Restoration and Adaptation initiatives.




Read more:
‘We know our community better than they do’: why local knowledge is key to disaster recovery in Gippsland


But we shouldn’t forget many Australian universities have considerable relevant expertise at their disposal, too. Not including the network of expertise and experience of universities means we may be shooting ourselves in the foot.

What’s more, the National Recovery and Resilience Agency intends to provide accredited training for people working in disaster recovery. The deep training and development expertise of universities is a perfect fit for this goal.

To really embed the benefits, we need to break down historical silos between national, state and local agencies. On-the-ground efforts for disaster risk reduction, emergency management and response, and the broad social aspects of recovery are largely state and local government responsibilities.

Crisis response planning and action is a team-based sport, so getting the federal, state and local governments — and the private sector — involved will help streamline the application of the new disaster policies and protocols embodied in the announced changes across the continent.




Read more:
National and state leaders may not always agree, but this hasn’t hindered our coronavirus response


We saw this type of team-based effort at a national level when the emergency national cabinet was established to oversee collaborative decision-making in response to the COVID-19 pandemic. It’s joined-up thinking that enables rapid and more complete decision- making.

In short, we need better collaboration. How we can work together and utilise all our capabilities and capacities are questions that need to be at the forefront of national thinking.


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

Paul Barnes, Research Fellow (Disaster & Urban Resilience), UNSW

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

‘We know our community better than they do’: why local knowledge is key to disaster recovery in Gippsland


Shutterstock

Celeste Young, Victoria University and Roger Jones, Victoria UniversityOvercoming the odds is second nature to the Gippsland community. The people in this region have seen it all — fires, floods, droughts and extreme weather. And every time, these capable, resourceful and independent communities bounce back.

However, recovery from bushfires of the 2019/2020 Black Summer followed by the COVID-19 pandemic has been different.

Even before these events, we were researching vulnerability to natural hazards, risk ownership and diversity and inclusion nationally as part of our work with the Bushfire and Natural Hazards Cooperative Research Centre.

Through a mix of interviews, focus groups and surveys, we sought insights about communities, how they recover after disaster and what factors have the greatest impact. We focused on community strengths and how to build on them.

Our recently released report, Growing the seeds: recovery, strength and capability in Gippsland communities, highlights that recovery is often non-linear. It’s not just the damage to infrastructure, houses, environment and farmland that makes recovery difficult; the emotional and physical toll is often gruelling as well.

The report identifies several opportunities for change, including the need for a long-term plan (five years minimum) for building community emergency management capability in the region — well before the next disaster strikes.

Our research highlights recovery is often non-linear, an observation well supported by other research in this field.
Growing the seeds report.

A brutal time

The 2019–20 fires damaged over half of the East Gippsland Shire, an area of over
1.16 million hectares. Over 400 dwellings and businesses were lost and four people lost their lives. Areas like Mallacoota were at acute risk. In some areas, communities were under threat for weeks and evacuated repeatedly, exhausting them before the recovery process began.

Then, the pandemic hit, disrupting the established pattern of recovery where people get together to make sense of what has happened and start to rebuild their communities. One person describe the timing as “brutal”. Another said:

When the fires happened, you had a couple of amazing people who stepped up, opened the hall, and everyone was coming in, and they started doing Friday night dinners and everyone was there. There were 200-odd people every Friday night and then COVID ended it.

Via online community consultations, interviews and focus groups, we asked community members to identify strengths that supported recovery and opportunities for change.

We also surveyed 614 people during October 2020 in fire-affected regions of Victoria and New South Wales, with 31% of respondents coming from Victoria and 69% from NSW.

When asked what strengths their community showed following the bushfires, they included generosity and kindness (69%), resilience (61%) and active volunteering (59%).


Growing the seeds report., Author provided

When asked to identify the main challenges since the bushfire, COVID was named as the main challenge (49%), followed by damage to the environment (39%), anxiety (31%) and overall fatigue (26%).


Growing the seeds report., Author provided

The combination of bushfires and the pandemic also created economic risks and disrupted supply chains. Small businesses make up 98% of the local economy, and many are heavily reliant on tourism.

Recovering through community strength and capability

Many of the strengths needed to drive recovery and resilience are already at the heart of these communities. These capabilities are more diverse and widespread than is often assumed.

There is considerable wealth and capacity in some areas, but also a high level of social and economic vulnerability, with some living hand-to-mouth.

There is significant local knowledge of risk management and recovery, which is often overlooked by experts coming in from outside. As one person told us:

You’ve got bureaucracy coming in from Melbourne who think that we’re just a bunch of country bumpkins who don’t quite know what we’re doing, yet we know our community better than they do.

Volunteer and informal economies are significant and underpin community resilience. Yet formal recovery strategies don’t target these areas very well; some people in the informal economy found they did not qualify for economic or business support at all.

The JobSeeker and JobKeeper programs helped maintain employment (albeit at levels of productivity that were lower than in the past). JobKeeper has now ended but support is still needed to boost productivity and help the local economy recover.

We also found:

  • government and some supporting agencies often lacked knowledge about the cultural, physical and social structures of different communities
  • some policies had perverse effects (for example, the HomeBuilder grant resulted in a lack of available builders)
  • programs and communication were often not tailored and did not accommodate the diverse needs of communities or specific cohorts within them
  • a lack of clarity as to what role the community have in response and recovery, and what risks they are responsible for
  • short-term allocation of resources and funding sometimes created an environment of uncertainty; for example, some participants raised concerns vulnerable community members may at risk when contracts for certain programs ran out, as the service offered would either cease or be led by a new contract-holder. As one person told us:

You can’t just bring someone in now and go, ‘Here you go, you take over all my people’, because the relationships and the trust that you build over this time, it’s not something you can hand over to someone else.

Knowing community strengths and supporting them

Recovery processes will never be perfect and we can also no longer assume communities will have time to recover from one disaster before the next arrives. As one person said:

People are suffering collective trauma, which creates anxiety and irritability. So, it is going to be difficult to move forward and I believe [name removed] will be a really changed place, this is something that will echo up and down along all fire-ravaged communities.

In natural hazard prone areas like Gippsland, it’s crucial to know what strengths already exist in the community so they can be harnessed when disaster hits. In other words, we need to find ways to support and grow community capabilities.

Listening to communities

It’s crucial communities, governments and the emergency services have a shared understanding of what the priorities are after a disaster and what can be realistically achieved.

A database of community capabilities would support more effective planning, policy-making and program development, as would a longer term collaborative project to identify and develop community capability.

Through listening to these communities we can learn from their experiences and support the development of community-led pathways to recovery.




Read more:
More than a decade after the Black Saturday fires, it’s time we got serious about long-term disaster recovery planning


If this article has raised issues for you, or if you’re concerned about someone
you know, call Lifeline on 13 11 14. 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

Celeste Young, Collaborative Research Fellow, Sustainable Industries and Liveable Cities (ISILC), Victoria University and Roger Jones, Professorial Research Fellow, Victoria University

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

NZ’s next large Alpine Fault quake is likely coming sooner than we thought, study shows


NASA/JPL/NGA, CC BY-ND

Jamie Howarth, Te Herenga Waka — Victoria University of Wellington and Rupert Sutherland, Te Herenga Waka — Victoria University of Wellington

Graphic of Alpine Fault
The Alpine Fault marks the boundary between the Pacific and Australian plates in the South Island of New Zealand.
Author provided

The chances of New Zealand’s Alpine Fault rupturing in a damaging earthquake in the next 50 years are much higher than previously thought, according to our research, published today.

The 850km Alpine Fault runs along the mountainous spine of the South Island, marking the boundary where the Australian and Pacific tectonic plates meet and grind against each other, forcing up the Southern Alps. Over the past 4,000 years, it has ruptured more than 20 times, on average around every 250 years.

Alpine Fault earthquakes are recorded in lake sediment deposits.

The last major earthquake on the Alpine Fault was in 1717. It shunted land horizontally by eight metres and uplifted the mountains a couple of metres. Large earthquakes on the fault tend to propagate uninhibited for hundreds of kilometres.

Until now, scientists thought the risk of a major earthquake in the next 50 years was about 30%. But our analysis of data from 20 previous earthquakes along 350 kilometres of the fault shows the probability of that earthquake occurring before 2068 is about 75%. We also calculated an 82% chance the earthquake will be of magnitude 8 or higher.

Alpine Fault earthquakes in space and time

From space, the fault appears like a straight line on the western side of the Southern Alps. But there are variations in the fault’s geometry (its orientation and the angle it dips into Earth’s crust) and the rate at which the two plates slip past each other.

These differences separate the fault into different segments. We thought the boundaries between these segments might be important for stopping earthquake ruptures, but we didn’t appreciate how important until now.

Graphic of Alpine Fault
Differences in geometry and the rate of slip between the tectonic plates create sections along the Alpine Fault.
Author provided

We examined evidence from 20 previous Alpine Fault ruptures recorded in sediments in four lakes and two swamps on the west coast of the South Island over the past 4,000 years. From this evidence, we built one of the most complete earthquake records of its kind.

Once we analysed and dated the sediments from lakes near the Alpine Fault, we were able to see new patterns in the distribution of earthquakes along the fault. One of our findings is a curious “earthquake gate” at the boundary between the fault’s south western and central segments. It appears to determine how large an Alpine Fault earthquake gets.

Some ruptures stop at the gate and produce major earthquakes in the magnitude 7 range. Ruptures that pass through the gate grow into great earthquakes of magnitude 8 or more. This pattern of stopping or letting ruptures pass through tends to occur in sequences, producing phases of major or great earthquakes through time.




Read more:
New Zealand’s Alpine Fault reveals extreme underground heat and fluid pressure


Forecasting the next Alpine Fault earthquake

From the record of past earthquakes it is possible to forecast the likelihood of a future earthquake (i.e. a 75% chance the fault will rupture in the next 50 years). But from these data alone it is not possible to estimate the magnitude of the next event.

For this we used a physics-based model of how earthquakes behave and applied it to the Alpine Fault, testing it against data from earlier earthquake sequences. This is the first time we have been able to use past earthquake data that span multiple large earthquakes and are of sufficient quality to allow us to evaluate how such models could be used in forecasting.

The physics-based model simulated Alpine Fault earthquake behaviour when we included the variations in fault geometry that define the different fault segments. When the simulation is combined with our record of past behaviour it is possible to estimate the magnitude of the next earthquake.




Read more:
Rocky icebergs and deep anchors – new research on how planetary forces shape the Earth’s surface


The Alpine Fault earthquake record shows the past three earthquakes ruptured through the earthquake gate and produced great (magnitude 8 or higher) earthquakes. Our simulations show that if three earthquakes passed through the gate, the next one is also likely to go through.

This means we’d expect the next earthquake to be similar to the last one in 1717, which ruptured along about 380km of the fault and had an estimated magnitude 8.1.

Our findings do not change the fact the Alpine Fault has always been and will continue to be hazardous. But now we can say the next earthquake will likely happen in the next 50 years.

We need to move beyond planning the immediate response to the next event, which has been done well through the Alpine Fault Magnitude 8 (AF8) programme, to thinking about how we make decisions about future investment to improve infrastructure and community preparedness.The Conversation

Jamie Howarth, Senior lecturer, Te Herenga Waka — Victoria University of Wellington and Rupert Sutherland, Professor of tectonics and geophysics, Te Herenga Waka — Victoria University of Wellington

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

Sydney’s disastrous flood wasn’t unprecedented: we’re about to enter a 50-year period of frequent, major floods


Tom Hubble, University of SydneyLast month’s flood in the Hawkesbury-Nepean River region of western Sydney peaked at a staggering 12.9 metres, with water engulfing road signs and reaching the tops of many houses.

There hasn’t been a major flood on the Hawkesbury-Nepean for more than 30 years, with the last comparable one occurring in 1990. Long-term Sydneysiders, however, will remember that 12 major floods occurred during the 40 years before 1990. Five of these were larger than last month’s flood.

So what’s going on? The long-term rainfall pattern in the region and corresponding river flow is cyclic in nature. This means 40 to 50 years of dry weather with infrequent small floods are followed by 40 to 50 years of wet weather with frequent major floods.

As river and floodplain residents take stock of the recent damage to their homes and plan necessary repairs, it’s vital they recognise more floods are on the way. Large, frequent floods can be expected to occur again within 10 or 20 years if — as expected — the historical pattern of rainfall and flooding repeats itself.

Living in a bathtub

Many of the 18,000 people who were evacuated live in and around a region known as the “Sackville Bathtub”. As the name suggests, this flat, low-lying section of the floodplain region was spectacularly affected.

The flooded Hawkesbury-Nepean River last month. Brown floodwater is evident between Penrith (right) and the Pacific Ocean (top left). The Sackville Bathtub is located left of centre.
Digital Earth Australia Map, Geoscience Australia, Tom Hubble

The Sackville Bathtub is located between Richmond and Sackville. It’s part of the Cumberland Plain area of Western Sydney and formed very slowly over 100 million years due to plate tectonic processes. The bathtub’s mudstone rock layers are folded into a broad, shallow, basin-shaped depression, which is surrounded by steep terrain.

Downstream of Sackville, the Hawkesbury-Nepean River flows through sandstone gorges and narrows in width. This creates a pinch-point that partially blocks the river channel.

Just as a bath plug sitting half-way over a plughole slows an emptying bath, the Sackville pinch-point causes the bathtub to fill during floods.

How the bathtub effect in the Hawkesbury-Nepean Valley causes floodwaters to back up and lead to deep and dangerous flooding.

Will raising the dam wall work?

The NSW state government is planning to raise the wall of the Warragamba Dam to help mitigate catastrophic floods in the region. But this may not be an effective solution.

Typically, somewhere between 40% and 60% of the floodwater that fills up the Sackville Bathtub comes from unimpeded, non-Warragamba sources. So, when the Hawkesbury-Nepean River floods, the bathtub is already quite full and causing significant problems before Warragamba begins to spill. The Warragamba water then raises the flood level, but often by only a couple of metres.

Raising Warragamba Dam’s wall as a mitigation measure will only control about half the floodwater, and won’t prevent major floods delivered by the Nepean and Grose rivers, which also feed into the region. This represents a small potential benefit for a very large cost.

The timing of observed flood peaks during the August 1986 Hawkesbury-Nepean flood, in relation to the time when Warragamba Dam began to spill. The arrival of Warragamba water in the Sackville Bathtub increased the flood depth only by about a metre above the floodwaters delivered earlier during the flood from the Grose and Nepean rivers.
Tom Hubble – Redrawn from data presented in Appendix One of the Hawkesbury-Nepean Flood Study; Infrastructure NSW 2019.

A long flooding period is on our doorstep

The idea of drought-dominated and flood-dominated periods for the Hawkesbury-Nepean River system was proposed in the mid-1970s by the University of Sydney’s Robin Warner. Since the late 1990’s, it hasn’t been the focus of much research.




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


He showed a century-long cycle of alternating periods of dry weather and small floods followed by wet weather and big floods is normal for Sydney. This means the March flood may not have come as a surprise to older residents of the Sackville Bathtub, who have a lived experience of the whole 40-50 year flooding cycle.

As a rough average, one major flood occurred every four years during the last wet-weather period between 1950 and 1990. The largest of this period occurred in November 1961. It filled the Sackville Bathtub to a depth of 15 metres and — like the June 1964 (14.6 metres) and March 1978 (14.5 metres) events — caused more widespread flooding than this year’s flood.

A photo of a flood that occured in Maitland in September 1950.
Sam Hood/NSW State Library/Flickr, CC BY

We’re currently 30 years into a dry period, which may be about to end. Conditions might stay dry for another 10 or 20 years.

These cycles are likely caused by natural, long-term “climate drivers” — long-term climatic fluctuations such as El Niño and La Niña, the Pacific Decadal Oscillation and the Indian Ocean Dipole, which are driven by oceanic current circulations. These global phenomena bring both benevolent weather and destructive weather to Australia.

Eastern Australia experiences decades-long periods of wetter weather when these climate drivers sync up with each other. When they’re out of sync, we get dry weather periods.




Read more:
A rare natural phenomenon brings severe drought to Australia. Climate change is making it more common


These long-term cycles are natural and have been operating for thousands of years, but climate change is amplifying and accelerating them. Dry periods are getting drier, wet periods are getting wetter.

The good news and bad news

The bad news is that 12-plus metre floods at Hawkesbury River (Windsor Bridge) are not all that unusual. There have been 24, 12-plus metre floods at Windsor Bridge since 1799.

The good news is meteorological forecasters are excellent at predicting when the storms that generate moderate, large and catastrophic floods are coming. We can expect several days’ to a week’s notice of the next big flood.

We can also prepare our individual and communal responses for more large and frequent floods on the Hawkesbury-Nepean. Residents of the area need to think about how they might live near the river as individuals. Decide what is precious and what you will fit into a car and trailer. Practice evacuating.

As a community, we must ensure the transport infrastructure and evacuation protocols minimise disruption to river and floodplain residents while maximising their safety. It’s particularly important we set up inclusive infrastructure to ensure disadvantaged people, who are disproportionately affected by disasters, also have a fighting chance to evacuate and survive.




Read more:
Not ‘if’, but ‘when’: city planners need to design for flooding. These examples show the way


Upgrading the escape routes that enable people to evacuate efficiently is absolutely vital. As is rethinking whether we should continue urban expansion in the Sackville Bathtub.

So remember, the next major flood is going to occur sooner than we would like. If you live in this region, you must start preparing. Or as a wise elder once said, “Live on a floodplain, own a boat!”


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

Tom Hubble, Associate Professor, University of Sydney

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

Floodplains aren’t separate to a river — they’re an extension of it. It’s time to change how we connect with them


Melissa Parsons, University of New England and Martin Thoms, University of New EnglandDramatic scenes of flood damage to homes, infrastructure and livelihoods have been with us on the nightly news in recent weeks. Many will be feeling the pain for years to come, as they contend with property damage, financial catastrophe and trauma.

But what if, for a moment, we removed the humans and their structures from these tragic images — what would we see?

We would see a natural process of river expansion and contraction, of rivers doing exactly what they’re supposed to do from time to time. We’d see them exceeding what we humans have deemed to be their boundaries and depositing sediment across their floodplains. We’d see reproductive opportunities for fish, frogs, birds and trees. The floods would also enrich the soils. Floods can be catastrophic for humans, but they are a natural part of an ecosystem from which we benefit.

These scenes clearly depict the intersection of humans and nature, and it’s not working out well for either side.




Read more:
5 ways the government can clean up the Murray-Darling Basin Plan


We must envision a new way of interacting with floodplains – these brilliant social-ecological systems that are not separate to rivers but rather part of the riverine landscape.

Humans can live on and with floodplains — but the way we do that has to change.

What is a floodplain?

Floodplains are relatively flat stretches of land located next to rivers. It helps to think of them as an extension of the river; it is natural and normal for a river to flood their adjacent plains.

Floodplains are composed of sediment the river has transported and then deposited, which makes them incredibly fertile. Flow and sediment regimes interacting over decades — or millennia — determine the physical and ecological character of floodplains, and the way they flood.

There are more than 15 generic floodplain types in Australia. Each harbours a unique set of evolutionary properties, physical features and ecosystems.

These influence the way floodwaters traverse floodplains, how long water remains on a floodplain, the velocity, turbulence and depth of floodwaters, and ecosystem responses to flooding. Floodplains are complex and highly variable.

Floodplains are also dynamic and ever-changing — and we should expect them to change even more in the coming years. Australian rivers have experienced regular periods of increased flood activity in the past 100 years.

And climate change is predicted to increase flood activity.




Read more:
5 ways the government can clean up the Murray-Darling Basin Plan


Humans benefit from floodplains

Floodplains are among the most productive ecosystems on the planet – they are biodiversity hotspots.

That’s in large part due to periodic flooding between different parts of a river-floodplain system; flooding is crucial to the function of floodplains. Without floods, these floodplains wouldn’t “work” — they would not be able to deliver the ecosystem services we benefit from. Those benefits include, but are not limited to:

  • food grown in these fertile soils
  • regulation of a balanced ecosystem
  • cultural heritage
  • transportation (as floodplains are easy to build roads on)
  • the supply of good quality drinking water
  • recreation.

The economic value of floodplain ecosystem services exceed US$25,681 per hectare. Roughly 25% of global terrestrial ecosystem services come from floodplains.

Humans are drawn to live on floodplains because of their productivity. In Australia, the floodplains of the Murray Darling Basin, heavily developed for agriculture, yield more than A$10 billion annually. These floodplain ecosystems provide an estimated A$187 billion per annum from their various ecosystem services.

However, the more we interrupt floodplain processes with development, the more we diminish the supply of ecosystem services.

The perils of living on floodplains

Putting the people back into the news footage reveals a social picture that is costly, traumatic and disruptive. The events of the past weeks have now brought into focus the perils of living on floodplains.

Humans have come up with ways to contend with this peril. Dams and levees. Land use planning. Building codes. Engineered floodscapes. Insurance. Emergency preparation systems and community engagement.

But if floodplains are a social-ecological system, where society gains great benefits but is also periodically placed at risk, which side should get the greatest policy attention? The humans or the ecosystem?

The answer is: both. But they also need to be better integrated.

Balancing the social with the ecological

Balancing the social and ecological aspects of floodplains requires a mindset change. We must combine community participation with research, resilience and adaptation to make long-term decisions about the future of these complex social-ecological systems.

If society wants to continue to derive the billions of dollars of benefits from floodplains, we need to ensure that flooding continues to occur on floodplains, and adapt to risk in imaginative and innovative ways that also protect the benefits.

Business as usual is not an option. The limitations of technocratic controls such as dams and levees should now be obvious. Time and time again, these have increased flood risk and failed to flood-proof the floodplain.

Rarely do such linear solutions solve complex problems in social-ecological systems. Linear solutions often exacerbate a problem or simply move it on to other parts of the system, creating social inequality, environmental decline and future risk.

The Australian government’s 2018 National Disaster Risk Reduction Framework sets the challenge to join up the built, social, economic and natural environments to address disaster risk in Australia.

Accepting the challenge requires a broader focus on balancing the social-ecological sides of Australia’s vast floodplains. Complexity, not linear thinking, must be embedded in the way we reimagine policy about floodplains and floods.

This requires transformative collaborations between government departments, researchers, business, and community stakeholders.


If this article has raised issues for you, or if you’re concerned about someone
you know, call Lifeline on 13 11 14. 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

Melissa Parsons, Senior Lecturer, Geography and Planning, University of New England and Martin Thoms, Professor of Physical Geography, University of New England

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