Catastrophic Queensland floods killed 600,000 cattle and devastated native species


Gabriel Crowley, James Cook University and Noel D Preece, James Cook University

In February, about 600,000 cattle were killed by catastrophic flooding across north Queensland’s Carpentaria Gulf plains.

The flood waters rose suddenly, forming a wall of water up to 70km wide. Record depths were reached along 500km of the Flinders River, submerging 25,000 square kilometres of country. Cattle were stranded. Many drowned.




Read more:
Queensland’s floods are so huge the only way to track them is from space


Even though cattleman Harry Batt lost 70% of his herd, he was more concerned about the wildlife. He said, “all the kangaroos, and bloody little marsupial mice and birds, they couldn’t handle it”.

Harry was right to be concerned. As our research, published today in Austral Ecology, reveals, floods sweeping Australia’s plains have disrupted native species for millions of years. Now, as climate change drives more intense flooding, we will see this effect intensify.

Flooding causes major disruptions to gene flow

February’s flood came ten years to the day after a far bigger flood on the adjoining river systems that submerged an area larger than Ireland. It was this flood that first drew our attention to the plight of native species.

Noel was asked by Northern Gulf Resource Management Group to survey wildlife in areas affected by the 2009 flood. Over the following four years, he found almost no ground-dwelling reptiles, despite them occurring elsewhere in the region. They appeared to have been washed away or drowned.

Biologists have long known that many species’ ranges are interrupted by the Gulf Plains. Hence, these floodplains are considered one of Australia’s most important biogeographic barriers: the Carpentarian Gap.

Many closely related species with a common ancestor are separated by this Gap, including the Golden-shouldered Parrot of Cape York Peninsula and the Hooded Parrot of the Northern Territory. They are thought to have separated around 7 million years ago.




Read more:
South-East Queensland is droughtier and floodier than we thought


The Gap also separates many other species, including birds, mammals, reptiles and butterflies, at the subspecies or genetic level. Even more species found on either side are just absent from the Gulf Plains.

Huge flooding across the Gulf Plains, including the Norman and Flinders Rivers, in February 2009.
NASA Worldview, CC BY-SA

Flood impacts are immense and under-appreciated

When biologists first tried to find a reason for these patterns, they only considered aridity. They proposed Australia’s arid zone expanded to the Gulf of Carpentaria during ice ages.

There is no evidence for this, but the misunderstanding is completely understandable.

Any dry-season visitor to the Gulf Plains will find a dry, inhospitable environment with few trees or shrubs for shade, cracked clay soils, and lots of flies. European explorers described the region as “God-forsaken”.

But it can be quite a different place in the wet season.

Rains in the Gulf are caused by the summer monsoonal troughs or cyclones. About once a decade, these generate massive downpours. Historical records show at least 14 major floods since 1870.

So, to us, it seemed floods rather than aridity could be the cause of the odd distributions of plants and animals.

We set out to see whether Noel’s findings could have been caused by flooding or whether other factors such as soil, vegetation or climate were more important.

We also wanted to know what other effects floods might have on the region’s ecosystem. Could floods, by eliminating trees and shrubs, be responsible for the hostile appearance of the region? Could ground-dwelling reptiles and birds be underrepresented, not just at Noel’s sites, but on floodplains across the area?

To find out, we divided the area into floodplains and higher-altitude land, and generated 10,000 random sites across the Gulf Plains. We extracted soil, vegetation and rainfall data from national information sources, and examined the patterns.

We found trees and shrubs were significantly less common on floodplains than on land above the flood zone, regardless of soil or rainfall, and tree cover was further reduced on cracking clays. We concluded the plain’s open, hostile appearance is caused by a combination of soils and flooding.

We then examined all gecko, skink and bird records from the Atlas of Living Australia.

We found ground-living reptiles and birds were much less common on the floodplains, regardless of vegetation or soil. As expected, reptiles were more sensitive to flooding than birds, which can fly to safety during floods.

Finally, we found the sites affected by the 2009 flood had significantly fewer geckos and skinks than other sites across the Gulf Plains.

Increased flooding from climate change could have major consequences

Our findings have evolutionary significance that extends into the future. Repeated disruption of species across their distributions affects gene flow and ultimately produces new species. If floods become more frequent, as expected under climate change, so might the rates at which new species form.

They also have serious land management implications. Climate change planning emphasises conserving river corridors as safe refuges from arid conditions. However, periodic scouring of many of the nation’s floodplains – expected to increase under climate change – means that this approach needs rethinking.




Read more:
Townsville floods show cities that don’t adapt to risks face disaster


We conclude that on the most arid occupied continent on Earth, unpredictable floods may cause the most disruption to the Australian plant and animal life.The Conversation

Gabriel Crowley, Adjunct Principal Research Fellow, James Cook University and Noel D Preece, Adjunct Asssociate Professor, James Cook University

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

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Heatwaves and flash floods: yes, this is Britain’s ‘new normal’


Hayley J. Fowler, Newcastle University

“It’s hard to believe, isn’t it, that we had a heatwave just last week?”

Those words were spoken by a BBC news presenter, in front of graphic images of fire service rescues, as heavy rain caused floods and landslides which closed many roads and railway lines. In recent days there have dramatic floods across the north of England, particularly around Manchester, the Peak District and Yorkshire.

For me, this is personal, as I am from the worst affected area. I went to high school where people spent the night in their Civic Hall. Three miles away from where I grew up, a dam holding back Toddbrook Reservoir has been at risk of collapse and the town of Whaley Bridge was evacuated. But I’m not surprised that we are seeing flash flooding and I expect it to get worse in the future.

I am a professor at Newcastle University, where I lead a large research group focused on understanding changes to intense rainfall events and flash floods. Over the past eight years we’ve been working closely with colleagues at the UK Met Office to develop new very high-resolution climate models that can simulate these very intense summer storms and therefore predict what might happen in a warming climate.

Our models tell us that by 2080 summers in the UK will be much hotter and drier. Heatwaves will be more common. In fact a report released by the Met Office on the same day as the latest flash floods tells us that heatwaves are already happening more often. When Cambridge recently hit 38.7℃, the UK became one of 12 countries to break its national temperature record this year.

The world is warming. But although UK average summer rainfall is predicted to decrease, our models tell us that when it does rain it will be more intense than has been the case. Flash flooding in the UK is generally caused by intense rainstorms, where more than 30mm falls in an hour. Climate models predict these will happen five times more often by 2080.

Part of the reason for this is the simple fact that warmer air can hold more moisture. But that’s too simple: the availability of moisture also increases in areas close to warm oceans – warmer sea surface temperatures cause more moisture to be evaporated into the atmosphere, providing additional fuel for these intense storms. And here’s the scary bit: the Atlantic Ocean provides a vast source of moisture for storms in the UK.

But that’s not the whole story. Heavy, short rain storms are intensifying more rapidly than would be expected with global warming (what we call the Clausius-Clapeyron relationship). Research also suggests that more intense storms can themselves grow bigger, and with both the intensity of the rainfall and the spatial footprint of the storm increasing, the total rainfall in an “event” could double.

What’s more, the larger storms seem to have an ability to draw in more moisture from the surrounding area and become even more intense: the additional energy (heating) fuelling the uplift of air within the storm’s core draws in even more moisture from the surface, allowing them to grow even larger, with more potential for flooding. These also provide the perfect ingredients for large hail storms.

So, it is entirely consistent that we might expect both more heatwaves and more intense summer thunderstorms in a warmer climate. We also know which areas of the country are already susceptible to these flash floods from our analysis of historical records of flooding. Newspapers have reported on the dramatic impacts of these floods for centuries and this has allowed my team to reconstruct a flash-flooding history of the UK.

Certain parts of the country are highly vulnerable as their rivers respond quickly to rainstorms. These rivers tend to be found in steep, upland catchments underlain by non-permeable rocks, mainly in the north and west of the UK. High-risk catchments also include urban areas where the ground is also non-permeable, for entirely different reasons.

Many of the towns reported to have suffered “biblical” flooding recently have suffered repeated flooding through history, but perhaps not within living memory. For example, Whaley Bridge is mentioned twice in the flood chronologies for events in June 1872 and July 1881:

On 19th [June 1872] the Goyt was 12 to 14 feet above its normal level. At Whaley Bridge houses near the river were completely flooded and people were taken into the chapel and inns … in Macclesfield a woman and child were drowned when the river Bollin overflowed. Two reservoirs burst in the vicinity.

This rich archive of knowledge, including the prevalence of flooding in certain towns, even specific roads, is something we should draw upon in planning both the emergency response to these flash floods and for reducing their future impact. We can learn a lot from the past in how to manage the greater risks of flooding the future will bring.The Conversation

Hayley J. Fowler, Professor of Climate Change Impacts, Newcastle University

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

Townsville floods show cities that don’t adapt to risks face disaster


Cecilia Bischeri, Griffith University

A flood-ravaged Townsville has captured public attention, highlighting the vulnerability of many of our cities to flooding. The extraordinary amount of rain is just one aspect of the disaster in Queensland’s third-biggest city. The flooding, increasing urban density, the management of the Ross River Dam, and the difficulties of dealing with byzantine insurance regulations have left the community with many questions about their future.

These questions won’t be resolved until we enhance the resilience of cities and communities against flooding. Adaptation needs to become an integral part of living with the extremes of the Australian environment. I discuss how to design and create resilient urban landscapes later in this article.




Read more:
Queensland’s floods are so huge the only way to track them is from space


Flood risk and insurance

Another issue that affects many households and businesses is the relationship between insurance claims and 1-in-100-year flood event overlay maps. Projected rises in flood risks under climate change have led to concerns that parts of Townsville and other cities will become “uninsurable” should the costs of cover become prohibitive for property owners.

Council flood data used for urban planning and land-use strategies is also used by insurers to assess the flood risk to individual properties. Insurers then price the risk accordingly.




Read more:
Lessons in resilience: what city planners can learn from Hobart’s floods


However, in extraordinary circumstances, when the flooded land is actually larger than the area marked by the flood overlay map, complications emerge. In fact, that part of the community living outside the map’s boundaries is considered flood-free. Thus, those pockets of the community may have chosen not to have flood insurance and not have emergency plans, which leaves them even worse off after floods. This is happening in Townsville.

Yet this is nothing new. Many people experienced very similar circumstances in 2011. Flood waters covered as much land as Germany and France combined. Several communities were left on their knees.

Notwithstanding the prompt and vast response of the federal government and Queensland’s state authorities, a few years later Townsville is going through something alarmingly similar.

Adaptation to create resilient cities

To find a solution, we need to rethink how to implement the Queensland Emergency Risk Management Framework. That is no easy task. However, it starts with shifting the perspective on what is considered a risk – in this case, a flooding event.

Floods, per se, are not a natural disaster. Floods are part of the natural context of Queensland as can be seen below, for instance, in the Channel Country.

Floods are part of the Australian landscape. Here trees mark the seasonal riverbeds in the Queensland outback between Cloncurry and Mount Isa.
Cecilia Bischeri, Author provided

The concept of adaptation as a built-in requirement of living in this environment then becomes pivotal. In designing and developing future-ready cities, we must aim to build resilient communities.

This is the ambitious project I am working on. It involves different figures and expertise with a shared vision and the support of government administrations that are willing to invest in a future beyond their elected term of office.

Ideas for Gold Coast Resilientscape

I live and work in the City of Gold Coast. Water is a fundamental part of the city’s character and beauty. In addition to the ocean, a complex system of waterways shapes a unique urban environment. However, this also exposes the city to a series of challenges, including flooding.

Last September, an updated flood overlay map was made available to the community. The map takes into account the projections of a 0.8 metre increase in the sea level and 10% increases in storm tide intensity and rainfall intensity.

These factors are reflected in the 1-in-100-year flood overlay. It shows undoubtedly that the boundaries between land and water are changeable.

Building walls between the city and water as the primary flood protection strategy is not a solution. A rigid border can actually intensify the catastrophe. New Orleans and the levee failures during the passage of Hurricane Katrina in 2005 provide a stark illustration of this.

Instead, what would happen and what would our cities look like if we designed green and public infrastructures that embody flooding as part of the natural context of our cities and territory?




Read more:
Design for flooding: how cities can make room for water


The current project, titled RESILIENTSCAPE: A Landscape for Gold Coast Urban Resilience, considers the role of architecture in enhancing the resilience of cities and communities against flooding. The proposal, in a nutshell, explores the possibilities that urban landscape design and implementation provide for resilience.

RESILIENTSCAPE focuses on the Nerang River catchment and the Gold Coast Regional Botanic Gardens, in the suburb of Benowa. The river and gardens were adopted as a case study for a broader strategy that aims to promote architectural solutions for a resilient City of Gold Coast. The project investigates the possibility of using existing green pockets along the Nerang River to store and retain excess water during floods.

Gold Coast Regional Botanic Gardens is one of the green areas along the Nerang River that could be used to store and retain flood water.
Batsv/Wikimedia Commons, CC BY-SA

These green spaces, however, will not just serve as “water tanks”. If mindfully planned, the green spaces can double up as public parks and facilities. This would enrich the community’s social realm and maximise their use and return on investment.

The design of a landscape responsive to flooding can, by improving local urban resilience, dramatically change the impact of these events.

The goal of creating urban areas that are adaptive to an impermanent water landscape is the main driver of the project. New Orleans after Hurricane Katrina and New York after Sandy are investing heavily in this direction and promoting international design competitions and community participation to mould a more resilient future. Queensland, what are we waiting for?




Read more:
Floods don’t occur randomly, so why do we still plan as if they do?



This article has been updated to clarify the use of flood data by insurers in assessing risk and the cost of cover.The Conversation

Cecilia Bischeri, Lecturer in Architecture, Griffith University

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

South-East Queensland is droughtier and floodier than we thought



File 20180620 137734 1bzxjzp.jpg?ixlib=rb 1.1
South-East Queensland residents need to prepare for more regular floods, according to new data.
Shutterstock

Jack Coates-Marnane, Griffith University; Joanne Burton, Griffith University; John Tibby, University of Adelaide; Jon Olley, Griffith University; Joseph M. McMahon, Griffith University, and Justine Kemp, Griffith University

New data recording the past 1,500 years of flows in the Brisbane River have revealed that South-East Queensland’s climate – once assumed to be largely stable – is in fact highly variable.

Until now, we have only had access to 200 years of weather records in South-East Queensland. But our new research used marine sediment cores (dirt from the bottom of the ocean) to reconstruct stream flows and rainfall over past millennia.

This shows that long droughts and regular floods are both prominent features in South-East Queensland’s climate.

This is concerning. Decisions about where we build infrastructure and how we use water have been based on the assumption that our climate – especially rainfall – is relatively stable.




Read more:
Old floods show Brisbane’s next big wet might be closer than we think


Archives of past climates

Natural archives of climate are preserved within things such as tree rings, coral skeletons, ice cores, lake or marine sediments. Examining them lets us extend our climate records back beyond documented history.

We can then undertake water planning in the context of a longer record of climate, instead of our short-term instrumental records.

In this study, we used sediment cores from Moreton Bay (next to the mouth of the Brisbane River) to reconstruct the river’s flow over the past 1,500 years. In these cores we measured various indicators of fresh water to reconstruct a record of streamflow and regional rainfall.

At the turn of the last millennium the region was in the middle of a prolonged dry spell that lasted some six centuries, from roughly the year 600 to 1200. After about 1350 the region became gradually wetter, with peaks revealing a series of extreme floods in the late 1600s and early 1700s. Large floods in the 1700s have also been documented in the upper reaches of the catchment, in the Lockyer Valley.

These broad shifts in regional rainfall and streamflow are linked to drivers of global climates, including hemispheric cooling and the El Niño-Southern Oscillation.




Read more:
Explainer: El Niño and La Niña


A cool La Niña-dominant climate that persisted from roughly 1350 until 1750 caused increased rainfall and reduced evaporation.

In addition, the southward displacement of monsoon troughs at this time may have increased the likelihood of cyclone-related weather systems reaching southern Queensland.

This information helps us contextualise the climate of the last 200 years and gives us some insights into how regional rainfall responds to shifts in global climate.

Wet and dry extremes

Over the past 20 years, South-East Queensland has experienced its fair share of extreme weather events. Severe floods have caused deaths and damaged infrastructure. Flooding cost the Australian economy some A$30 billion in 2011.

Regular droughts may mean South-East Queensland needs to rethink water resource strategies.
Shutterstock

The millennium drought, which in this region was most severe from 2003-08, resulted in widespread water shortages. This prompted major investment in the South-East Queensland Water Grid, a connected network of dams, water treatment plants, reservoirs, pump stations and pipelines.

So far Queensland has coped with everything Mother Nature has thrown at it. But what if extreme floods and droughts became the norm rather than the exception?




Read more:
Floods don’t occur randomly, so why do we still plan as if they do?


Water quality is getting worse

The 2011 and 2013 floods highlighted the vulnerability to these extreme events of Brisbane’s major water treatment facility at Mt Crosby. The drinking water supply to the city in 2013 became too muddy for purification. The 2011 flood was also alarmingly muddy.

Such events also threaten the ecosystem health of downstream waterways, including the iconic Moreton Bay

Our reconstruction found that big floods over the past 1,500 years rivalled the size of floods in recorded history (1893, 1974 and 2011), but the level of sediment in the water of more recent floods seems to be unprecedented.

This indicates that historical and ongoing land-use changes in the Brisbane River catchment are contributing to more abrupt and erosive floods.

This will continue unless better land management techniques are adopted to improve the resilience of catchments to extreme weather events.

What does this mean for the future?

We are learning that over the last millennium natural climate and rainfall have been more variable than previously thought. This means that modern anthropogenic climate change may be exacerbated by a background of already high natural climate variability.

In addition, our water infrastructure has been built based on a narrow understanding of natural climate variability, limited to the last 200 years. This may mean the quantity of reliable long-term freshwater resources in eastern Australia has been overestimated.


The Conversation


Read more:
Droughts & flooding rains: what is due to climate change?


Jack Coates-Marnane, Post-doctoral research fellow, Griffith University; Joanne Burton, Adjunct Research Fellow, Griffith University; John Tibby, Senior Lecturer in Environmental Change, University of Adelaide; Jon Olley, Professor of Water Science, Griffith University; Joseph M. McMahon, PhD candidate, Griffith University, and Justine Kemp, Senior Research Fellow in Geomorphology, Griffith University

This article was originally published on The Conversation. Read the original article.

Floods don’t occur randomly, so why do we still plan as if they do?


Anthony Kiem, University of Newcastle

Most major floods in South East Queensland arrive in five-year bursts, once every 40 years or so, according to our new research.

Yet flood estimation, protection and management approaches are still designed on the basis that flood risk stays the same all the time – despite clear evidence that it doesn’t.

We analysed historical flooding data from ten major catchments in South East Queensland. As we report in the Australasian Journal of Water Resources, 80% of significant floods arrived during five-year windows, with 35-year gaps of relative dryness between.




Read more:
Old floods show Brisbane’s next big wet might be closer than we think


The early 1970s brought a succession of severe floods to South East Queensland. This was followed in the 1980s by a raft of floodplain development projects, together with extensive research on floodplains and flooding risk, carried out by a group of researchers who described themselves as the “Roadshow” because of their frequent visits to flood-prone regions.

Throughout the 1980s, some Roadshow members noticed that large floods in South East Queensland seemed to follow a 40-year cycle, with five-year periods of high flood risk separated by 35 years of lower flood risk. They speculated that the next “1974 flood” (a reference to a devastating flood that hit Brisbane and South East Queensland that year) would arrive some time around 2013 .

Sure enough, South East Queensland was once again hit by large floods in January 2011 and January 2013.

Evidently, large floods in South East Queensland are not random. This is a problem, given that development policies and engineering practice, by and large, still assume that they are.

History repeating

In 1931, the Queensland meteorologist and farmer Inigo Jones linked the Brisbane River’s floods to the Bruckner Cycle of solar activity, which he determined to be 35 years long, but which has since been found to vary from 35 to 45 years.

In 1972, flood engineer John Ward argued that flood frequency distributions differ in space and time because higher flows originate from a variety of different rainfall mechanisms. At the time, minimal insight was available into what those different rainfall mechanisms were.

In the 1990s, drought research in Queensland by, among others, researchers Roger Stone and Ken Brook and John Carter identified cyclical variations in Queensland rainfall associated with the Southern Oscillation Index (SOI), supporting the idea of non-random occurrence of floods.

In 1999, Australian hydrologist Robert French also noticed that irregular clustering of flood events was associated with the SOI, and pointed out that flood planning needed to take into account more than just seasonal or year to year variability.

More recently, flood incidence has been strongly linked to large-scale ocean processes such as the El Niño/Southern Oscillation (ENSO) and the Interdecadal Pacific Oscillation (IPO). These phenomena seem to have a marked effect on eastern Australian rainfall variability, and therefore on the risk of both floods and drought.

Is the 40-year cycle real?

We compiled records of major floods in South East Queensland between 1890 and 2014. As the table below shows, roughly 80% of large historical floods happened within a series of five-year flood-prone periods, despite these periods together representing only 16% of the study period.

The South East Queensland study area (approximately indicated by the orange box) and the 10 catchments analysed in this study.

Timing of the largest flood events within the 40-year cycles. Superscripts next to each flood event indicate the ranking of that flood event in that catchment (that is, the largest flood in each catchment is ranked 1).

On average, the number of large floods per year was 4.9 times higher within the five-year flood-prone periods.

Not only were floods more frequent, they were also more severe, with flood heights 41% higher during the five-year flood-prone periods than at other times.

Even though a few large floods occurred outside the five-year flood-prone periods, the 40-year cycle of flooding in South East Queensland appears to be a genuine phenomenon.

What drives the cycle?

The most likely physical explanation for cyclic or non-random flooding is the IPO, which is rather like the ENSO cycle except on longer time scales. The IPO influences eastern Australia’s climate indirectly, by affecting both the magnitude and frequency of ENSO impacts.

Recent “negative phases” of the IPO – meaning warmer than average Pacific Ocean temperatures north and south of the tropics – happened roughly during 1870–95, 1945-76, and 1999–present.

If we compare these with the five-year flood-prone periods in the table above, we can see that with the exception of 1930–34, all five-year flood-prone periods happened during these negative IPO events. Interestingly, the large floods in the 1950s and 1960s happened outside the five-year flood-prone periods identified by the 1980s Roadshow, but do align with IPO negative conditions.




Read more:
Planning for a rainy day: there’s still lots to learn about Australia’s flood patterns


In spite of all this evidence, most engineers and flood planners still assume that floods occur randomly and that flood risk is the same all the time. Phrases like “one in 100-year event” or “1% annual exceedance probability” are routinely used to describe floods, despite the fact that for some years and decades the risk is significantly higher. This gives a false sense of security during times when major floods are much more likely.

If this approach continues, then every few decades our flood defences will not be as reliable as we thought – a fact to which many Queenslanders can now attest.

We need new approaches to deal with the reality that large flood events do not occur randomly. It would arguably be more sensible to separate flood records into two (or more) categories – one for times when flood risk is “normal” and another for periods where the risk is higher – and then reevaluate flood frequency distributions and flood risks for each category. Decision makers then get a more realistic estimate of the true risk of flooding which leads to more informed and more resilient flood planning and defences.

This new approach might also help plan for the changes to flood risk expected in the future, whether from climate change, land use change, or whatever else the oceans and skies throw at us.


The ConversationThis article was coauthored by Greg McMahon, a Brisbane-based independent consultant on flood risks and Academic Chair at Rhodes Group Australia.

Anthony Kiem, Associate Professor – Hydroclimatology, University of Newcastle

This article was originally published on The Conversation. Read the original article.

Globally, floods seem to be decreasing even as extreme rainfall rises. Why?


Seth Westra, University of Adelaide and Hong Xuan Do, University of Adelaide

Over the past decade we have seen a substantial increase in our scientific understanding of how climate change affects extreme rainfall events. Not only do our climate models suggest that heavy rainfall events will intensify as the atmosphere warms, but we have also seen these projections start to become reality, with observed increases in rainfall intensity in two-thirds of the places covered by our global database.

Given this, we might expect that the risk of floods should be increasing globally as well. When it comes to global flood damage, the economic losses increased from roughly US$7 billion per year in the 1980s to US$24 billion per year in 2001-11 (adjusted for inflation).

It would be natural to conclude that at least some of this should be attributable to climate change. However, we know that our global population is increasing rapidly and that more people now live in flood-prone areas, particularly in developing countries. Our assets are also becoming more valuable – one only needs to look at rising Australian house prices to see that the values of homes at risk of flooding would be much greater now than they used to be in decades past.

So how much of this change in flood risk is really attributable to the observed changes in extreme rainfall? This is where the story gets much more complicated, with our new research showing that this question is still a long way from being answered.

Are floods on the rise?

To understand whether flood risk is changing – even after accounting for changes in population or asset value – we looked at measurements of the highest water flows at a given location for each year of record.

This sort of data is easy to collect, and as such we have reasonably reliable records to study. There are more than 9,000 streamflow gauges around the world, some of which have been collecting data for more than a century. We can thus determine when and how often each location has experienced particularly high volumes of water flow (called “large streamflow events”), and work out whether its flood frequency has changed.

A streamflow gauging station in Scotland.
Jim Barton/Wikimedia Commons, CC BY-SA

We found that many more locations have experienced a decrease in large streamflow events than have experienced an increase. These decreases are particularly evident in tropical, arid, and humid snowy climate regions, whereas locations with increasing trends were more prevalent in temperate regions.

To understand our findings, we must first look closely at the factors that could alter the frequency and magnitude of these large streamflow events. These factors are many and varied, and not all of them are related directly to climate. For example, land-use changes, regulated water releases (through dam operations), and the construction of channels or flood levées could all influence streamflow measurements.

We looked into this further by focusing on water catchments that do not have large upstream dams, and have not experienced large changes in forest cover that would alter water runoff patterns. Interestingly, this barely changed our results – we still found more locations with decreasing trends than increasing trends.

The Australian Bureau of Meteorology and similar agencies worldwide have also gone to great lengths to assemble “reference hydrological stations”, in catchments that have experienced relatively limited human change. Studies that used these sorts of stations in Australia, North America and Europe are all still consistent with our findings – namely that most stations show either limited changes or decreases in large streamflow events, depending on their location.

What can we say about future flood risk?

So what about the apparent contradiction between the observed increases in extreme rainfall and the observed decreases in large streamflow events? As noted above, our results don’t seem to be heavily influenced by changes in land use, so this is unlikely to be the primary explanation.

An alternative explanation is that, perhaps counterintuitively, extreme rainfall is not the only cause of floods. If one considers the 2010-11 floods in Queensland, these happened because of heavy rainfall in December and January, but an important part of the picture is that the catchments were already “primed” for flooding by a very wet spring.

Perhaps the way in which catchments are primed for floods is changing. This would make sense, because climate change also can cause higher potential moisture loss from soils and plants, and reductions in average annual rainfall in many parts of the world, such as has been projected for large parts of Australia.

This could mean that catchments in many parts of the world are getting drier on average, which might mean that extreme rainfall events, when they do arrive, are less likely to trigger floods. But testing this hypothesis is difficult, so the jury is still out on whether this can explain our findings.

Despite these uncertainties, we can be confident that the impacts of climate change on flooding will be much more nuanced than is commonly appreciated, with decreases in some places and increases in others.

Your own flood risk will probably be determined by your local geography. If you live in a low-lying catchment close to the ocean (and therefore affected by sea level rise), you’re probably at increased risk. If you’re in a small urban catchment that is sensitive to short sharp storms, there is emerging evidence that you may be at increased risk too. But for larger rural catchments, or places where floods are generally caused by snow melt, the outcome is far harder to predict and certain locations may see a decrease in flooding.

All of this means that a one-size-fits-all approach is unlikely to be suitable if we are to allocate our resources wisely in adjusting to future flood risk. We must also think about the effects of climate change in a broader context that includes changes to land-use planning, investment in flood protection infrastructure, flood insurance, early warning systems, and so on.

The ConversationOnly by taking a holistic view, informed by the best available science, can we truly minimise risk and maximise our resilience to future floods.

Seth Westra, Associate Professor, School of Civil, Environmental and Mining Engineering, University of Adelaide and Hong Xuan Do, PhD candidate in Civil and Environmental Engineering, University of Adelaide

This article was originally published on The Conversation. Read the original article.

Was Tasmania’s summer of fires and floods a glimpse of its climate future?


Alistair Hobday, CSIRO; Eric Oliver, University of Tasmania; Jan McDonald, University of Tasmania, and Michael Grose, CSIRO

Drought, fires, floods, marine heatwaves – Tasmania has had a tough time this summer. These events damaged its natural environment, including world heritage forests and alpine areas, and affected homes, businesses and energy security.

In past decades, climate-related warming of Tasmania’s land and ocean environments has seen dozens of marine species moving south, contributed to dieback in several tree species, and encouraged businesses and people from mainland Australia to relocate. These slow changes don’t generate a lot of attention, but this summer’s events have made people sit up and take notice.

If climate change will produce conditions that we have never seen before, did Tasmania just get a glimpse of this future?

Hot summer

After the coldest winter in half a century, Tasmania experienced a warm and very dry spring in 2015, including a record dry October. During this time there was a strong El Niño event in the Pacific Ocean and a positive Indian Ocean Dipole event, both of which influence Tasmania’s climate.

The dry spring was followed by Tasmania’s warmest summer since records began in 1910, with temperatures 1.78℃ above the long-term average. Many regions, especially the west coast, stayed dry during the summer – a pattern consistent with climate projections. The dry spring and summer led to a reduction in available water, including a reduction of inflows into reservoirs.

Left: September-November 2015 rainfall, relative to the long-term average. Right: December 2015-February 2016 temperatures, relative to the long-term average.
Bureau of Meteorology, Author provided

Is warmer better? Not with fires and floods

Tourists and locals alike enjoyed the clear, warm days – but these conditions came at a cost, priming Tasmania for damaging bushfires. Three big lightning storms struck, including one on January 13 that delivered almost 2,000 lightning strikes and sparked many fires, particularly in the state’s northwest.

By the end of February, more than 300 fires had burned more than 120,000 hectares, including more than 1% of Tasmania’s World Heritage Area – alpine areas that had not burnt since the end of the last ice age some 8,000 years ago. Their fire-sensitive cushion plants and endemic pine forests are unlikely to recover, due to the loss of peat and soils.

Meanwhile, the state’s emergency resources were further stretched by heavy rain at the end of January. This caused flash flooding in several east coast towns, some of which received their highest rainfall ever. Launceston experienced its second-wettest day on record, while Gray recorded 221 mm in one day, and 489 mm over four days.

Flooding and road closures isolated parts of the state for several days, and many businesses (particularly tourism) suffered weeks of disruption. The extreme rainfall was caused by an intense low-pressure system – the Climate Futures for Tasmania project has predicted that this kind of event will become more frequent in the state’s northeast under a warming climate.

Warm seas

This summer, an extended marine heatwave also developed off eastern Tasmania. Temperatures were 4.4℃ above average, partly due to the warm East Australian Current extending southwards. The heatwave began on December 3, 2015, and was ongoing as of April 17 – the longest such event recorded in Tasmania since satellite records began in 1982. It began just days after the end of the second-longest marine heatwave on record, from August 31 to November 28, 2015, although that event was less intense.

Anatomy of a marine heatwave. Top left: summer sea surface temperatures relative to seasonal average. Top right: ocean temperature over time; red shaded region shows the ongoing heatwave. Bottom panels: duration (left) and intensity (right) of all recorded heatwaves; the ongoing event is shown in red.
Eric Oliver

As well as months of near-constant heat stress, oyster farms along the east coast were devastated by a new disease, Pacific Oyster Mortality Syndrome, which killed 100% of juvenile oysters at some farms. The disease, which has previously affected New South Wales oyster farms, is thought to be linked to unusually warm water temperatures, although this is not yet proven.

Compounding the damage

Tasmania is often seen as having a mild climate that is less vulnerable to damage from climate change. It has even been portrayed as a “climate refuge”. But if this summer was a taste of things to come, Tasmania may be less resilient than many have believed.

The spring and summer weather also hit Tasmania’s hydroelectric dams, which were already run down during the short-lived carbon price as Tasmania sold clean renewable power to the mainland. Dam levels are at an all-time low and continue to fall.

The situation has escalated into a looming energy crisis, because the state’s connection to the national electricity grid – the Basslink cable – has not been operational since late December. The state faces the prospect of meeting winter energy demand by running 200 leased diesel generators, at a cost of A$43 million and making major carbon emissions that can only exacerbate the climate-related problems that are already stretching the state’s emergency response capability.

Is this summer’s experience a window on the future? Further study into the causes of climate events, known as “detection and attribution”, can help us untangle the human influence from natural factors.

If we do see the fingerprint of human influence on this summer, Tasmania and every other state and territory should take in the view and plan accordingly. The likely concurrence of multiple events in the future – such as Tasmania’s simultaneous fires and floods at either end of the island and a heatwave offshore – demands that governments and communities devise new strategies and mobilise extra resources.

This will require unprecedented coordination and cooperation between governments at all levels, and between governments, citizens, and community and business groups. Done well, the island state could show other parts of Australia how to prepare for a future with no precedent.

The Conversation

Alistair Hobday, Senior Principal Research Scientist – Oceans and Atmosphere, CSIRO; Eric Oliver, Postdoctoral Fellow (Physical Oceanography and Climate), University of Tasmania; Jan McDonald, Professor of Environmental Law, University of Tasmania, and Michael Grose, Climate Projections Scientist, CSIRO

This article was originally published on The Conversation. Read the original article.