In this study, the potential impact of climate change on southeast Australia is estimated. Simulations from two CSIRO climate models using two greenhouse gas and aerosol emissions scenarios are combined with historical weather observations to assess the changes to fire weather expected by 2020 and 2050. In general, fire weather conditions are expected to worsen. By 2020, the increase in ΣFFDI is generally 0-4% in the low scenarios and 0-10% in the high scenarios. By 2050, the increase in generally 0-8% (low) and 10-30% (high). The largest changes are expected in northern New South Wales. Little change is expected in Tasmania. With this increase in ΣFFDI, a larger number of days with a Fire Danger Rating of ‘very high’ or ‘extreme’ are also expected. The number of ‘extreme’ fire danger days generally increases 5-25% for the low scenarios and 15-65% for the high scenarios. By 2050, the increases are generally 10-50% in the low scenarios and100- 300% for the high scenarios. The seasons are likely to become longer, starting earlier in the year.
These results are placed in the context of the current climate and its tendencies. During the last several years in southeast Australia, including the 2006-07 season, particularly severe fire weather conditions have been observed. In many cases, the conditions far exceed the projections in the high scenarios of 2050. Are the models (or our methodology) too conservative or is some other factor at work?
Examining longer-term observations at eight stations, back to the early 1940s in many cases, reveals considerable inter-decadal variability. Periods of increasing and decreasing fire weather danger are apparent in the record. The peaks of these ‘cycles’ occur roughly every 20 years and the time series might suggest that we are at (or near) a peak, although there is no physical basis on which to estimate when or to what extent a decrease might occur.
There is also evidence for anthropogenic climate change being a driver of this upswing. The current peaks in ΣFFDI are much higher than observed in past instances. There are also a greater number of VHE days at many locales. There is also the suggestion that the fire season is starting earlier. Finally, the severity and length of the recent drought [e.g. Nicholls 2006] and the associated fire danger has not been seen in the available records.
The hypothesis posited in this study is that the naturally occurring peak in fire danger due to interdecadal variability may have been exacerbated by climate change. The test of this hypothesis comes over the next few years to decades. If correct, then it might be expected that fire weather conditions will return to levels something more along the lines of those suggested in the 2020 scenarios. If fire danger conditions stay this high, then the conclusion must be that the models used to make these projections are too conservative. Whatever the case, continued observation, as well as improved modelling are required to resolve this question.
What of the human impacts of these projected changes? The last few years, particularly the 2006-07 fire season, may provide an indication for the future. Early season starts suggest a smaller window for pre-season fuel-reduction burns. Logically, more frequent and more intense fires suggest that more resources will be required to maintain current levels of bushfire suppression. Shorter intervals between fires, such as those which burned in eastern Victoria during 2002-03 and 2006-07, may significantly alter ecosystems and threaten biodiversity. It is hoped that planning authorities can use this information in the development of adaptation strategies.
– Lucas, Hennessy, Mills and Bathols : “Bushfire weather in Southeast Australia: recent trends and projected climate change impacts”, Bushfire CRC, Australian Bureau of Meteorology and CSIRO Marine and Atmospheric Research. [Cheers for the link from Clive Hamilton in Crikey!]
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