Bushfire weather in SE Australia: Recent trends and projected climate change impacts
Lucas, C., K. Hennessy, G Mills and J. Bathols (2007), "Bushfire weather in SE Australia: Recent trends and projected climate change impacts", Bushfire CRC, Australian Bureau of Meteorology and CSIRO, Melbourne.
The number of ‘very high’ fire danger days generally increases 2-13% by 2020 for the low scenarios and 10-30% for the high scenarios (Table E1). By 2050, the range is much broader, generally 5-23% for the low scenarios and 20-100% for the high scenarios. The number of ‘extreme’ fire danger days generally increases 5-25% by 2020 for the low scenarios and 15-65% for the high scenarios (Table E1). By 2050, the increases are generally 10-50% for the low scenarios and 100-300% for the high scenarios.
‘Very extreme’ days tend to occur only once every 2 to 11 years at most sites. By 2020, the low scenarios show little change in frequency, although notable increases occur at A mberley, Charleville, Bendigo, Cobar, Dubbo and Williamtown. The 2020 high scenarios indicate that very extreme’ days may occur about twice as often at many sites. By 2050, the low scenarios are similar to those for the 2020 high scenarios, while the 2050 high scenarios indicate a four to five-fold increase in frequency at many sites.
Roger Jones, The Conversation, 22 October 2013
In research I did with colleagues earlier this year we looked at the Fire Danger Index calculated by the Bureau of Meteorology, and compared how it changed compared to temperature over time in Victoria.
South-east Australia saw a temperature change of about 0.8C when we compared temperatures before 1996 and after 1997. We know that it got drier after 1997 too.
We then compared this data to the Forest Fire Danger Index, to see if it showed the same pattern. We analysed fire data from nine stations in Victoria and did a non-linear analysis. We found that fire danger in Victoria increased by over a third after 1996, compared to 1972-1996. The current level of fire danger is equivalent to the worst case projected for 2050, from an earlier analysis for the Climate Institute.
While it’s impossible to say categorically that the situation is the same in NSW, we know that these changes are generally applicable across south-east Australia. So it’s likely to be a similar case: fire and climate change are linked.
IPCC: Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation
(Field, C.B., V. Barros, T.F. Stocker, D. Qin, D.J. Dokken, K.L. Ebi, M.D. Mastrandrea, K.J. Mach, G.-K. Plattner, S.K. Allen, M. Tignor, and P.M. Midgley (editors)
Box 4-1: Evolution of Climate, Exposure, and Vulnerability – The Melbourne Fires, 7 February 2009
The fires in the Australian state of Victoria, on 7 February 2009, demonstrate the evolution of risk through the relationships between the weather- and climate-related phenomena of a decade-long drought, record extreme heat, and record low humidity of 5% (Karoly, 2010; Trewin and Vermont, 2010) interacting with rapidly increasing exposure. Together the climate phenomena created the conditions for major uncontrollable wildfires (Victorian Bushfires Royal Commission, 2010).
The long antecedent drought, record heat, and a 35-day period with no rain immediately before the fires turned areas normally seen as low to medium wildfire risk into very dry high-risk locations. A rapidly expanding urban-bush interface and valuable infrastructure (Berry, 2003; Burnley and Murphy, 2004; Costello, 2007, 2009) provided the values exposed and the potential for extreme impacts that was realized with the loss of 173 lives and considerable tangible and intangible damage. There was a mixture of natural and human sources of ignition, showing that human agency can trigger such fires and extreme impacts.
Many people were not well-prepared physically or psychologically for the fires, and this influenced the level of loss and damage they incurred. Levels of physical and mental health also affected people’s vulnerability. Many individuals with ongoing medical conditions, special needs because of their age, or other impairments struggled to cope with the extreme heat and were reliant on others to respond safely (Handmer et al., 2010). However, capacity to recover in a general sense was high for humans and human activities through insurance, government support, private donations, and nongovernmental organizations (NGOs) and was variable for the affected bush with some species and ecosystems benefitting (Lindenmayer et al., 2010; Banks et al., 2011; see also Case Study 9.2.2).
Chapter 3 details projected changes in climate extremes for this region that could increase fire risk, in particular warm temperature extremes, heat waves, and dryness (see Table 3-3 for summary).
Wildfires around Canberra in January 2003 caused AUS$ 400 million damage (Lavorel and Steffen, 2004), with about 500 houses destroyed, four people killed, and hundreds injured. Three of the city’s four water storage reservoirs were contaminated for several months by sediment- laden runoff (Hennessy et al., 2007). The 2009 fire in the state of Victoria caused immense damage (see Box 4-1 and Case Study 9.2.2).
An increase in fire danger in Australia is associated with a reduced interval between fire events, increased fire intensity, a decrease in fire extinguishments, and faster fire spread (Hennessy et al., 2007). In southeast Australia, the frequency of very high and extreme fire danger days is expected to rise 15 to 70% by 2050 (Hennessy et al., 2006). By the 2080s, the number of days with very high and extreme fire danger are projected to increase by 10 to 50% in eastern areas of New Zealand, the Bay of Plenty, Wellington, and Nelson regions (Pearce et al., 2005), with even higher increases (up to 60%) in some western areas. In both Australia and New Zealand, the fire season length is expected to be extended, with the window of opportunity for fuel reduction burning shifting toward winter (Hennessy et al., 2007).
Changes in Australian fire weather between 1973 and 2010
Clarke, H., C. Lucas and P. Smith (2012) "Changes in Australian fire weather between 1973 and 2010". Int. J. Climatol., DOI: 10.1002/joc.3480
A data set of observed fire weather in Australia from 1973–2010 is analysed for trends using the McArthur Forest Fire Danger Index (FFDI). Annual cumulative FFDI, which integrates daily fire weather across the year, increased significantly at 16 of 38 stations. Annual 90th percentile FFDI increased significantly at 24 stations over the same period. None of the stations examined recorded a significant decrease in FFDI. There is an overall bias in the number of significant increases towards the southeast of the continent, while the largest trends occur in the interior of the continent and the smallest occur near the coast. The largest increases in seasonal FFDI occurred during spring and autumn, although with different spatial patterns, while summer recorded the fewest significant trends. These trends suggest increased fire weather conditions at many locations across Australia, due to both increased magnitude of FFDI and a lengthened fire season. Although these trends are consistent with projected impacts of climate change on FFDI, this study cannot separate the influence of climate change, if any, with that of natural variability.
The recent bushfires and extreme heat wave in southeast Australia
Karoly, D.J. (2009) "The recent bushfires and extreme heat wave in southeast Australia". Bulletin of the Australian Meteorological and Oceanographic Society 22: 10-13
See also: Bushfires and extreme heat in south-east Australia
Although formal attribution studies quantifying the influence of climate change on the increased likelihood of extreme fire danger in southeast Australia have not been undertaken yet, it is very likely that there has been such an influence. Increases in maximum temperature have been attributed to anthropogenic climate change. In addition, reduced rainfall and low relative humidity are expected in southern Australia due to anthropogenic climate change. The FFDI for a number of sites in Victoria on 7 February reached unprecedented levels, ranging from 120 to 190, much higher than the fire weather conditions on Black Friday or Ash Wednesday, and well above the “catastrophic” fire danger rating (Lucas et al., 2007).
Of course, the impacts of anthropogenic climate change on bushfires in southeast Australia or elsewhere in the world are not new or unexpected. In 2007, the IPCC Fourth Assessment Report WGII chapter “Australia and New Zealand” (Hennessy et al., 2007) concluded ‘An increase in fire danger in Australia is likely to be associated with a reduced interval between fires, increased fire intensity, a decrease in fire extinguishments and faster fire spread. In south-east Australia, the frequency of very high and extreme fire danger days is likely to rise 4-25% by 2020 and 15-70% by 2050.’ Similarly, observed and expected increases in forest fire activity have been linked to climate change in the western US (Westerling et al., 2006), in Canada (Gillett et al., 2004) and in Spain (Pausas, 2004).
While it is difficult to separate the influences of climate variability, climate change, and changes in fire management strategies on the observed increases in fire activity, it is clear that climate change is increasing the likelihood of environmental conditions associated with extreme fire danger in southeast Australia and a number of other parts of the world.
Regional signatures of future fire weather over eastern Australia from global climate models
Clarke, H.G., P.L. Smith and A.J. Pitman (2011), "Regional signatures of future fire weather over eastern Australia from global climate models". Int. J. Wildland Fire, 20, 550-562.
Skill-selected global climate models were used to explore the effect of future climate change on regional bushfire weather in eastern Australia. Daily Forest Fire Danger Index (FFDI) was calculated in four regions of differing rainfall seasonality for the 20th century, 2050 and 2100 using the A2 scenario from the Special Report on Emissions Scenarios. Projected changes in FFDI vary along a latitudinal gradient. In summer rainfall-dominated tropical north-east Australia, mean and extreme FFDI are projected to decrease or remain close to 20th century levels. In the uniform and winter rainfall regions, which occupy south-east continental Australia, FFDI is projected to increase strongly by 2100. Projections fall between these two extremes for the summer rainfall region, which lies between the uniform and summer tropical rainfall zones. Based on these changes in fire weather, the fire season is projected to start earlier in the uniform and winter rainfall regions, potentially leading to a longer overall fire season.
The sensitivity of Australian Fire danger to climate change
Willliams, A.A., D.J. Karoly and N. Tapper (2001), "The sensitivity of Australian Fire danger to climate change". Climatic Change 49:171-191
Global climate change, such as that due to the proposed enhanced greenhouse effect, is likely to have a significant effect on biosphere-atmosphere interactions, including bushfire regimes. This study quantifies the possible impact of climate change on fire regimes by estimating changes in fire weather and the McArthur Forest Fire Danger Index (FDI), an index that is used throughout Australia to estimate fire danger. The CSIRO 9-level general circulation model (CSIRO9 GCM) is used to simulate daily and seasonal fire danger for the present Australian climate and for a doubled- CO2 climate. The impact assessment includes validation of the GCMs daily control simulation and the derivation of ‘correction factors’ which improve the accuracy of the fire danger simulation. In summary, the general impact of doubled-CO2 is to increase fire danger at all sites by increasing the number of days of very high and extreme fire danger. Seasonal fire danger responds most to the large CO2-induced changes in maximum temperature.