Last year was a time of exceptional weather and record-breaking heat according to the Bureau of Meteorology’s annual climate statement, which was released last night.
The Bureau issued four Special Climate Statements relating to “extreme” and “abnormal” heat, and reported a number of broken climate records.
One of the headline stories for the year was drought across eastern Australia — centred on New South Wales, but also affecting Victoria, eastern South Australia and southern Queensland.
With the whole of NSW declared in drought during the latter half of 2018, this drought will be recorded as one of the more significant in Australia’s history, ranking alongside the Millennium, 1960s, World War Two and Federation Droughts. Of those historic droughts, only the Millennium Drought saw similar, accompanying high temperatures.
The below-average rainfall has persisted for around two years across much of NSW and adjacent regions. The drought conditions were particularly severe in the recent spring period, with low rainfall, persistently high temperatures, and record high evaporation.
This exceptionally dry period was influenced by sea surface temperatures to the west of the continent. Perhaps fortuitously, a developing El Niño in the Pacific Ocean failed to mature in the second half of the year. An El Niño would have typically exerted a further drying influence on eastern Australia.
The dry conditions in eastern states were severe enough to see Australia record its lowest September rainfall on record, and the second-lowest on record for any month — behind April 1902, during the prolonged Federation Drought. Over 2018, Australia’s annual rainfall was 11% below average, and the lowest recorded since 2005, during the Millennium Drought.
In contrast, above-average rainfall was recorded across parts of the tropical north, and most significantly in the Kimberley, consistent with recent trends of increasing rainfall in that region.
The drought conditions were exacerbated by record or near-record temperatures across many parts of the country. It was Australia’s third warmest year on record, behind 2013 and 2005. Daytime maximum temperatures were the warmest on record for NSW and Victoria, and second-warmest for South Australia, the Northern Territory and Australia as a whole.
Persistent dry conditions through winter are typically associated with low soil moisture and heatwaves in the following spring and summer, and 2018 followed this pattern — with the added contribution of a warming climate.
The year ended with some record-breaking heat events. Perhaps the most significant of these was the extreme heat along the central and northern Queensland coast in late November and early December, which saw maximum daytime temperatures of 42.6 °C in Cairns and 44.9 °C in Proserpine on the 26th of November.
These temperatures, combined with persistent dry conditions in the preceding months, saw catastrophic fire weather and bushfires along 600km of the Queensland coast, an event that fire agencies have called unprecedented for the state.
The year ended with a burst of heat over the Christmas-New Year period, with temperatures at least 10 degrees warmer than average across southern South Australia, most of Victoria and southern NSW, leading to Australia’s warmest December on record.
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Large parts of Australia are facing a hotter and drier summer than average, according to the Bureau of Meteorology’s summer outlook.
Drier than average conditions are likely for much of northern Australia. Most of the country has at least an 80% chance of experiencing warmer than average day and night-time temperatures.
The threat of bushfire will remain high, with few signs of the sustained rain needed to reduce fire risk or make a significant dent in the ongoing drought.
Expect extreme heat
Large parts of Western Australia, most of Queensland and the Top End of the Northern Territory are expected to be drier than usual. Further south, the rest of the country shows no strong push towards a wetter or drier than average summer, which is a change for parts of the southeast compared to recent months.
Queensland has already seen some extraordinary record-breaking heat in recent days, with summer yet to truly begin. With the summer outlook predicting warmer days and nights, combined with recent dry conditions and our long-term trend of increasing temperatures, some extreme highs are likely this summer.
All of this means above-normal bushfire potential in eastern Australia, across New South Wales, Victoria and Queensland. The bushfire outlook, also released today, notes that rain in areas of eastern Australia during spring, while welcome, was not enough to recover from the long-term dry conditions. The current wet conditions across parts of coastal New South Wales will help, but it will not take long once hot and dry conditions return for vegetation to dry out.
What about El Niño?
The Bureau is currently at El Niño ALERT, which means a roughly 70% chance of El Niño developing this season.
However, not all the ducks are lined up. While ocean temperatures have already warmed to El Niño levels, to declare a proper “event” there must also be a corresponding response in the atmosphere to reinforce the ocean – this hasn’t happened yet.
That said, climate models expect this event to arrive in the coming months. The outlook has factored in that chance, and the conditions predicted are largely consistent with what we would expect during El Niño. In summer, this includes drier weather in parts of northern Australia, and warmer summer days.
Once an El Niño is in place, weather systems across southern Australia tend to be more mobile. This can mean shorter but more intense heatwaves in Victoria and southern South Australia. However, in New South Wales and Queensland, El Niño is associated with both longer and more intense heat waves.
The exact reason why the states are affected differently is complicated, but relates to the fast-moving cold fronts and troughs that sweep through Victoria and South Australia in the summertime, creating cool changes. These weather systems don’t influence areas further north so when hot air arrives, it takes longer to clear.
The heavy rains seen in parts of eastern Australia in October and November have provided some welcome short-term relief to drought-stricken farmers, but longer-term rainfall relief has not arrived yet. If El Niño arrives, this widespread relief may only be on the cards in autumn.
Once again, the summer of 2018 in the Northern Hemisphere has brought us an epidemic of major wildfires.
These burn forests, houses and other structures, displace thousands of people and animals, and cause major disruptions in people’s lives. The huge burden of simply firefighting has become a year-round task costing billions of dollars, let alone the cost of the destruction. The smoke veil can extend hundreds or even thousands of miles, affecting air quality and visibility. To many people, it has become very clear that human-induced climate change plays a major role by greatly increasing the risk of wildfire.
Yet it seems the role of climate change is seldom mentioned in many or even most news stories about the multitude of fires and heat waves. In part this is because the issue of attribution is not usually clear. The argument is that there have always been wildfires, and how can we attribute any particular wildfire to climate change?
As a climate scientist, I can say this is the wrong framing of the problem. Global warming does not cause wildfires. The proximate cause is often human carelessness (cigarette butts, camp fires not extinguished properly, etc.), or natural, from “dry lightning” whereby a thunderstorm produces lightning but little rain. Rather, global warming exacerbates the conditions and raises the risk of wildfire.
Even so, there is huge complexity and variability from one fire to the next, and hence the attribution can become complex. Instead, the way to think about this is from the standpoint of basic science – in this case, physics.
Global warming is happening
To understand the interplay between global warming and wildfires, consider what’s happening to our planet.
The composition of the atmosphere is changing from human activities: There has been over a 40 percent increase in carbon dioxide, mainly from fossil fuel burning since the 1800s, and over half of the increase is since 1985. Other heat-trapping gases (methane, nitrous oxide, etc.) are also increasing in concentration in the atmosphere from human activities. The rates are accelerating, not declining (as hoped for with the Paris agreement).
This leads to an energy imbalance for the planet.
Heat-trapping gases in the atmosphere act as a blanket and inhibit the infrared radiation – that is, heat from the Earth – from escaping back into space to offset the continual radiation coming from the sun. As these gases build up, more of this energy, mostly in the form of heat, remains in our atmosphere. The energy raises the temperature of the land, oceans and atmosphere, melts ice, thaws permafrost, and fuels the water cycle through evaporation.
Moreover, we can estimate Earth’s energy imbalance quite well: It amounts to about 1 watt per square meter, or about 500 terawatts globally.
While this factor is small compared with the natural flow of energy through the system, which is 240 watts per square meter, it is large compared with all other direct effects of human activities. For instance, the electrical power generation in the U.S. last year averaged 0.46 terawatts.
The extra heat is always the same sign and it is spread across the globe. Accordingly, where this energy accumulates matters.
Tracking the Earth’s energy imbalance
Heat also accumulates in melting ice, causing melting Arctic sea ice and glacier losses in Greenland and Antarctica. This adds water to the ocean, and so the sea level rises from this as well, rising at a rate of over 3 milimeters year, or over a foot per century.
On land, the effects of the energy imbalance are complicated by water. If water is present, the heat mainly goes into evaporation and drying, and that feeds moisture into storms, which produce heavier rain. But the effects do not accumulate provided that it rains on and off.
However, in a dry spell or drought, the heat accumulates. Firstly, it dries things out, and then secondly it raises temperatures. Of course, “it never rains in southern California” according to the 1970s pop song, at least in the summer half year.
So water acts as the air conditioner of the planet. In the absence of water, the excess heat effects accumulate on land both by drying everything out and wilting plants, and by raising temperatures. In turn, this leads to heat waves and increased risk of wildfire. These factors apply in regions in the western U.S. and in regions with Mediterranean climates. Indeed many of the recent wildfires have occurred not only in the West in the United States, but also in Portugal, Spain, Greece, and other parts of the Mediterranean.
The conditions can also develop in other parts of the world when strong high pressure weather domes (anticyclones) stagnate, as can happen in part by chance, or with increased odds in some weather patterns such as those established by either La Niña or El Niño events (in different places). It is expected that these dry spots move around from year to year, but that their abundance increases over time, as is clearly happening.
How big is the energy imbalance effect over land? Well, 1 Watt per square meter over a month, if accumulated, is equivalent to 720 Watts per square meter over one hour. 720 Watts is equivalent to full power in a small microwave oven. One square meter is about 10 square feet. Hence, after one month this is equivalent to: one microwave oven at full power every square foot for six minutes. No wonder things catch on fire!
Coming back to the original question of wildfires and global warming, this explains the argument: there is extra heat available from climate change and the above indicates just how large it is.
In reality there is moisture in the soil, and plants have root systems that tap soil moisture and delay the effects before they begin to wilt, so that it typically takes over two months for the effects to be large enough to fully set the stage for wildfires. On a day to day basis, the effect is small enough to be lost in the normal weather variability. But after a dry spell of over a month, the risk is noticeably higher. And of course the global mean surface temperature is also going up.
“We can’t attribute a single event to climate change” has been a mantra of climate scientists for a long time. It has recently changed, however.
As in the wildfires example, there has been a realization that climate scientists may be able to make useful statements by assuming that the weather events themselves are relatively unaffected by climate change. This is a good assumption.
Also, climate scientists cannot say that extreme events are due to global warming, because that is a poorly posed question. However, we can say it is highly likely that they would not have had such extreme impacts without global warming. Indeed, all weather events are affected by climate change because the environment in which they occur is warmer and moister than it used to be.
In particular, by focusing on Earth’s Energy Imbalance, new research is expected to advance the understanding of what is happening, and why, and what it implies for the future.
An out-of-season bushfire raged through Sydney’s southwest at the weekend, burning more than 2,400 hectares and threatening homes.
As the fire season extends and heatwaves become more frequent, it’s vital to preserve our natural protections. My research, recently released in the journal Austral Ecology, contradict one of the central assumptions in Australian fire management – that forest accumulate fuel over time and become increasingly flammable.
I looked at every fire in every forest in the Australian Alps National Parks and found that mature forests are dramatically less likely to burn. Perhaps surprisingly, once a forest is several decades old it becomes one of our best defences against large bushfires.
The English approach
Within decades of the first graziers taking land in the Australian Alps, observers noticed that English-style management had unintended consequences for an Australian landscape.
In the British Isles, grazing rangelands had been created in the moors by regular burning over thousands of years, and this approach was imported wholesale to Australia’s mountains.
By 1893, however, the botanist Richard Helms had observed that as little as a year after fires were introduced to clear the land, “the scrub and underwood spring up more densely than ever”.
It’s true that, as in the rest of the country, many shrubs in the Alps are germinated by fire. However, the Alps also lie in a climatic zone where many trees are easily killed by fire. As a result, fire produces dense regrowth, and in the worst cases, removes the forest canopy that is essential to maintaining a still, moist micro-climate. Fires burning in this regrowth have abundant dry fuel, and they are exposed to the full strength of the wind.
Theoretically, that should make regrowth more flammable than old growth, but it is at odds with the widespread assumption that fuels accumulate over time to make old forests the most flammable. Which is the case then? Are old forests more or less flammable than regrowth?
36 million case studies
Looking back over 58 years of mapped fires in the 12 national parks and reserves that make up the Australian Alps National Parks, I asked a simple question: when a wildfire burnt the mountains, did it favour one age of forest over another? If there were equal amounts of forest burnt say, five years, 10 years or 50 years ago, did fires on average burn more in one of those ages than another?
It’s not an entirely new question; people have often studied what happened when a fire crossed into recently burnt areas.
However, instead of just looking at part of a fire, I looked at every hectare it had burnt as separate case study. Instead of only looking at recent fires, I looked at every recorded fire in every forest across the Australian Alps National Parks. Instead of a handful of case studies, I now had 36 million of them.
Consistent with all of the other studies, I found that forests became more flammable in the years after they were burnt; but this is where the similarity ended. Rather than stop there as the other studies have done, I pushed past this line and found something striking. Regardless of which forest I examined, it became dramatically less likely to burn when it matured after 14 to 28 years.
The most marked response of these was in the tall, wet Ash forests. These have been unlikely to burn for about three years after a fire, but then the regrowth comes in. Until these trees are about 21 years old, Ash forests are one of the most flammable parts of the mountains, but after this, their flammability drops markedly. When our old Ash forest is burnt, it is condemned to two decades in which it is more than eight times as flammable.
The forests across the Alps have survived by constructing communities that keep fires small; but their defences are being broken down in the hotter, drier climate we are creating. Roughly the same area of the Victorian Alps was burnt by wildfire in the 10 years from 2003-2014 as had been burnt in the previous 50 years.
More fire means more flammable forests, which in turn mean more fire; it’s a positive feedback that can accelerate until fire-sensitive ecosystems such as the Ash collapse into permanently more flammable shrublands. Knowing this, however, gives us tools.
Old forests are assets to be protected, and priority can be given to nursing older regrowth into its mature stages. It may be the eleventh hour, but we’re better placed now to stand with the forests and add what we can to their fight to survive climate change.
Over the past year the global media has been full of reports of catastrophic fires in California, the Mediterranean, Chile and elsewhere. One suggested reason for increases in catastrophic wildfires has been human-induced climate change. Higher temperatures, drier weather and windier conditions all increase the impact of fires.
While climate change indeed raises the risk of wildfires, our research shows that another way humans can change patterns of fire activity is by introducing flammable plants to new environments.
Plantations of highly flammable exotic species, such as pines and eucalypts, probably helped to fuel the recent catastrophic fires in Portugal and in Chile. In arid regions, such as parts of the US southwest, the introduction of exotic grasses has transformed shrublands, as fires increase in severity.
Invasive plants and fire
One of the main ways flammable invasive plants can have long-lasting impacts on an ecosystem comes from positive fire-vegetation feedbacks. Such feedbacks can occur when a flammable weed invades a less fire-prone ecosystem. By changing the available fuel the invader makes fires more likely and often hotter.
If the invading species has characteristics that allow it to outcompete native species after a fire, then it will further dominate the ecosystem. Such traits include thick bark, the ability to resprout following fire, or seeds that survive burning. This invasion will likely lead to more fires, changing the species composition and function of the ecosystem in a “fire begets fire” cycle. Extreme examples of this dynamic are where flammable grasses or shrubs invade forests, leading to loss of the forest ecosystems.
We wanted to understand how invasive plants interact with other species when burned in combination. To explore the mechanisms underpinning such feedbacks, we examined how invasive plants might change the nature of a fire when burned together with native species.
We collected 70cm shoots of four globally invasive species (of both high and low flammability) and burned them in pairwise combinations with New Zealand native trees and shrubs to determine which characteristics of a fire could be attributed to the invasive plants.
We found that overall flammability was largely driven by the most flammable species in the mixture, showing how highly flammable weeds could set in motion fire-vegetation feedbacks.
We established that a greater difference in flammability between the two species led to a larger influence of the more flammable species on overall flammability. This outcome suggests weeds that are much more flammable than the invaded community can have larger impacts on fire patterns.
Importantly, we also showed the influence of the highly flammable species was independent of its biomass, meaning highly flammable weeds may impact community flammability even at low abundances.
When we looked closer at the different components of flammability (combustibility, ignitability, consumability and sustainability) we found some important nuances in our results.
While the maximum temperature reached in our burns (combustibility) and the ignition speed (ignitability) were both most influenced by the more flammable species, consumability (the amount of biomass burned) and sustainability (how long the fire burns) were equally influenced by both the more flammable and less flammable species.
In short, more flammable weeds will cause a fire to ignite more quickly and burn hotter.
However, less flammable species can reduce the duration of a fire compared to when a more flammable species is burnt alone. These results could have important ecological implications, as the longer a fire burns the more likely it is to kill plants: low-flammability plants could reduce this impact.
Managing weeds to reduce fire impacts
Even low abundances of highly flammable invasive weeds could set in motion positive fire-vegetation feedbacks that lead to drastic changes to ecosystems. If this result holds when our shoot-scale experiments are repeated using field trials, then land managers should work quickly to remove even small infestations of highly flammable species, such as gorse (Ulex europaeus) and prickly hakea (Hakea sericea).
Conversely, the role of low flammability plants in extinguishing fires further supports the suggestion that the strategic planting of such species across the landscape as “green firebreaks” could be a useful fire management tool.
In any case, our “mixed grill” study further highlights the role of exotic plants in fuelling hotter wildfires.
Tim Curran, Senior Lecturer in Ecology, Lincoln University, New Zealand; George Perry, Professor, School of Environment, and Sarah Wyse, Early Career Research Fellow, The Royal Botanic Gardens, Kew and Research Fellow, School of Environment
California is burning – a sentence we’ve heard far too often this year. Sydney is currently on bushfire alert, as firefighters battle a fire in the Hunter Valley region and temperatures are set to top 40℃.
A cocktail of factors, from climate change to centuries of ignoring indigenous burning practises, means that catastrophic fires are likely to become more common.
One of Australia’s favourite fire prevention measures is prescribed burning – using carefully controlled fires to clear out flammable materials. We’re almost obsessed with it. Indeed, it seems the outcome of every major inquiry is that we need to do more of it.
The Royal Commission inquiry that followed Victoria’s 2009 Black Saturday fires recommended that 5% of all public land in Victoria be treated per year – a doctrine that was subsequently dropped due to impracticality.
Yet our research, published today in the International Journal of Wildland Fire, modelled thousands of fires in Tasmania and found that nearly a third of the state would have to be burned to effectively lower the risk of bushfires.
The question of how much to burn and where is a puzzle we must solve, especially given the inherent risk, issues caused by smoke smoke and shrinking weather windows for safe burning due to climate change.
Why use computer simulations?
The major problem fire science faces is gathering data. Landscape-scale experiments involving extreme fire are rare, for obvious reasons of risk and cost. When a major bushfire happens, all the resources go into putting it out and protecting people. Nobody has the time to painstakingly collect data on how fast it is moving and what it is burning. We are therefore restricted to a few limited data sources to reconstruct the behaviour and impact of fire: we can analyse the scar on the landscape after a fire, look at case studies, or run simulations of computer models.
Most research on the effectiveness of prescribed burning has been at a local scale. We need to start thinking bigger: how can we mitigate the effect of multiple large fires in a region like Tasmania or Southeastern Australia? What is the cumulative effect of different prescribed burning strategies?
To answer these questions, we create models using mathematical equations to simulate the behaviour of fires across actual landscapes. These models include the effects of vegetation type, terrain and fuel loads, under specific weather conditions. If we simulate thousands of these fires we can get an idea of where fire risk is the highest, and how effective prescribed burning is at reducing that risk.
The island of Tasmania offers the perfect study system. Self-contained, with a wide array of vegetation types and fire regimes, it offers an ideal opportunity to see how fire behaves across a diverse landscape. Perhaps more interestingly, the island contains large areas of flammable landscape surrounding globally unique ecosystems and numerous towns and villages. Obviously, we cannot set fire to all of Tasmania in real life, but computer simulations make it possible!
So, encouraged by the Tasmanian Fire Service, who initiated our research, we simulated tens of thousands of fires across Tasmania under a range of prescribed burning scenarios.
Prescribed fire can be effective, in theory
The first scenario we looked at was the best-case scenario: what happens if we perform prescribed burning on all the vegetation that can handle it, given theoretically unlimited resources? It is possible this approximates the sustained and skillful burning by Tasmanian Aboriginal peoples.
Wildfire simulations following this scenario suggested that such an approach would be extremely effective. Importantly, we saw significant reductions in fire activity even in areas where prescribed burning is impossible (for example, due to the presence of people).
Unfortunately, this best-case approach, while interesting from a theoretical perspective, would require prescribed burning over more than 30% of Tasmania in one year.
We also analysed the effects of 12 more realistic scenarios. These realistic plans were less than half as efficient as the best-case scenario at reducing fire activity.
On average, 3 hectares of prescribed burning would reduce wildfire extent by roughly 1ha in grasslands and dry forests.
In other flammable Tasmanian vegetation types like buttongrass sedgelands and heathlands, the reduction in wildfire was even smaller. This is obviously better than no prescribed burning, but it highlights the fact that this is a relatively inefficient tool, and given the costs and potential drawbacks, should be used only where it is most needed.
This is a fundamental conundrum of prescribed burning: though it is quite effective in theory, the extent to which we would need to implement it to affect fire behaviour across the entire state is completely unachievable.
Therefore, it is imperative that we not just blindly burn a pre-ordained fraction of the landscape. Rather, we must carefully design localised prescribed burning interventions to reduce risk to communities.
We need a multi-tool approach
Our study has shown that while prescribed burning can be quite effective in certain scenarios, it has serious constraints. Additionally, while we analysed these scenarios under bad fire weather, we were not able to analyse the kind of catastrophic days in which the effect of prescribed burning is seriously reduced, with howling dry winds and stupefying heat.
In Hobart this is of particular concern, as the city is surrounded by tall, wet eucalypt forests that have had fifty years grow dense understoreys since the 1967 Black Tuesday fires. These have the potential to cause some of the most intense fires on the planet should conditions get dry enough. Prescribed burning is impossible in these forests.
To combat fire risk we must take a multi-pronged approach that includes innovative strategies, such as designing new spatial patterns for prescribed burning, manually removing fuels from areas in which prescribed burning is not possible, improving the standards for buildings and defensible spaces, and most importantly, engaging the community in all of this.
Only by attacking this problem from multiple angles, and through close collaboration with the community and all levels of government, can we effectively face our fiery future.