During the the spring and summer of 2019-2020, Australia experienced a catastrophic bushfire season with tragic loss of life and extensive destruction of and damage to property, natural landscapes and native and domesticated animals.
The full economic losses are yet to be calculated but the timing of the crisis, during the traditional Australian summer break, has had a serious impact on domestic and international tourism.
Following is a visual explanation and summary of the causes and effects of the bushfire emergency as it was in early February 2020 (at the time of writing and production) and with some weeks of the usual annual bushfires season in the southern states of Australia yet to go.
We look at some of the record-breaking statistics and put this year’s fire season in the context of major fire emergencies and events throughout the past 100 years. We describe the forces and systems that drive weather and climate in our own region and place them into the context of warming climate trends globally. We show the processes in which large intense bushfires create their own weather, which in turn exacerbates their intensity and size, and how, in this season, such events have been witnessed in numbers never seen before.



Australia’s most destructive fires
How do we measure destruction? Human cost takes precedence, with fatalities and homes destroyed being the most common measure of a fire’s destructiveness. Cost to the natural environment is more difficult to quantify but can be gauged by the amount of area burnt.

A change in the weather
In Australia, 2019 was officially the hottest and driest year since records began (Figure 2) with 18 December officially the hottest day ever with a mean national temperature of 41.9oC. The country as a whole was 1.52oC above the Bureau of Meteorology’s (BOM) 1961–1990 average. Global temperatures for 2019 were 1.1oC above the 1961–1990 average, making it the second- warmest year globally since 1880.
Long-term climate trends show clear warming (Figure 1) with a resulting increase in the duration and intensity of the annual bushfire season. Australia has warmed by 1.4oC since 1910 with most of that increase taking effect from 1950 onwards. Nine of our 10 warmest years have occurred since 2005 including each year since 2013.
The national total rainfall for 2019 was 40 per cent below average (Figure 3), making it the driest year since records began, although some northern regions saw above average rain in the early months of 2019, leading to flooding in parts of Queensland. Low humidity has increased fuel loads and made previously cool, moist and fire-resistant temperate rainforest gullies more susceptible to fire than ever before.
Australia has seen long periods of either wet or dry weather throughout recorded meteorological history and current trends are in part attributable to natural variability, but there are high levels of scientific confidence in the role played by human-induced climate change in the weather patterns that led to the optimum conditions for the 2019–2020 catastrophic bushfire season. Longer and more intense fire seasons are reducing the effectiveness of existing fire management strategies.


Australia’s highly variable climate is influenced by a range of oceanic climate systems, in particular the El Niño-Southern Oscillation Index (ENSO) in the Pacific Ocean, the Indian Ocean Dipole (IOD) and the Southern Annular Mode (SAM) over the Southern Ocean.
While 2019 saw a neutral El Niño mode, a strong positive IOD, characterised by cooler waters in the Indian Ocean off northern Australia and warmer waters off Africa, contributed to the lack of rainfall across southern Australia. Long-term observations indicate that positive IODs have increased in frequency and strength since the 1960s. This is likely to continue with climate change, which is also causing the SAM to become more positive. This moves storm tracks south, reducing winter rain over southern regions as part of a longer- term drying trend. In spring 2019 an unexpected warming event over the South Pole – a Sudden Stratospheric Warming – shifted the SAM into temporary negative mode. This drew hot air from the centre across southern Queensland and into the south-east regions.
This increased temperatures, decreased cloud cover, exacerbated existing drought conditions and lowered soil moisture, making fuels drier and more prone to burning, heightening the risk of large bushfires.
Fire weather is largely monitored by the Forest Fire Danger Index (FFDI), which estimates the potential fire danger based on observations of temperature, humidity, wind speed and a drought factor to represent fuel dryness. Daily FFDI values can be accumulated during longer periods of time and these values for spring 2019 were the highest on record for 60 per cent of Australia, significantly higher than the previous highest values in 2002. By the start of September 2019, much of south-eastern Australia was already primed for high fire danger ratings, heralding the start of what would become a catastrophic fire season that would kill 33 people, including nine firefighters, destroy 3000 homes and burn more than 16 million hectares of land with a devastating impact on native biodiversity.

Bushfires create their own deadly weather
Along with weather that creates optimum conditions for destructive bushfires, the fires themselves can create their own weather. When a number of factors come together, including the type of terrain, extremely hot bushfires that feature intense areas of flaming that extend a long way back from the fire front can develop into deadly firestorms. Extreme heat generated from such fires sends dense plumes of smoke as far as 15km up into the atmosphere. Depending on atmospheric conditions at these altitudes, smoke plumes can trigger a type of fire thunderstorm known as a pyrocumulonimbus, or pyroCb for short. Research suggests that bushfires can be made more severe by feedback mechanisms driven by the atmospheric instability that results in the formation of pyroCbs.
PyroCbs are visible as tall, billowing smoke clouds with a flat base and anvil-shaped head. If the bushfire is powerful enough and the atmospheric conditions unstable, thunderstorms can lead to downburst winds, strong inflow, fire tornadoes and lightning strikes. They can cause dangerous and unpredictable bushfire behaviour with strong, rapidly changing winds and large ember attacks that help spread the fire quickly, making it difficult for firefighters to manage. The incidence of pyroCb events is increasing as Australia’s bushfire seasons lengthen and the intensity of fires grows.
In this 2019–2020 fire season, more than 52 pyroCbs have so far been observed, far exceeding any previous records. Climate modelling indicates that unabated global warming will cause further increases in the potential for the type of extreme bushfires that lead to pyroCb events in the future.

Data sources and acknowledgments:
Infographic design Mike Ellott; Graphics Mike Rossi; Cartography Will Pringle; PyroCb Illustration Michael Payne; Infographic concept and main text Chrissie Goldrick; text annotations Mike Rossi; Data research Chrissie Goldrick and Mike Rossi; additional research Rebecca Cotton; Climate and weather graphs, information and data courtesy of the Australian Bureau of Meteorology; Other data courtesy of The Bushfire and Natural Hazards CRC; ARC Centre of Excellence for Climate Extremes; Bushfire statistics: Dept of Home Affairs, NSW Rural Fire Service, SA Country Fire Service, Victoria Country Fire Authority, WA Dept of Fire and Emergency Services, The Air Quality Index, NSW Dept. of Energy and the Environment, Copernicus: European Union’s Earth Observation Programme, UNEP, Meat and Livestock Australia, ABC Fact Check Unit, University of Sydney (School of Life and Environmental Sciences), Insurance Council of Australia. AG thanks Rick McRae of the ACT Emergency Services Agency for his generous assistance with the preparation of the pyroCb graphic and Alvin Stone, ARC Centre of Excellence for Climate Extremes, for his assistance with fact checking. Figures and statistics correct at time of printing but subject to change.