A detailed historical record of McArthur's Forest Fire Danger Index (FFDI) has been completed for many stations in south-eastern Australia, including the states of Victoria, New South Wales, South Australia, Tasmania and southern portions of Queensland. This study uses records beginning in 1973. Many extend back to 1957, with some looking back to the 1940s.
The effects of climate change are estimated using the CSIRO CCAM Mk 2 and Mk 3 climate model and two of the IPCC emissions scenarios. From these model runs, the changes in deciles of the base model climate are estimated for each station and each month. Changes in wind speed, relative humidity, temperature and rainfall centred around 2020 and 2050 are used. These changes to the distribution are then applied to the observed historical data. From this, new distributions of FFDI are computed.
In general, results show an increase in fire danger with the effects of climate change. Changes are smaller by 2020, with a 0-10% increase in cumulative FFDI (daily FFDI values summed over a whole year), a proxy for fire danger. By 2050, changes of up to 25% are seen. These changes are largest in the interior portions of New South Wales.
The second question is address through statistical analysis of the historical record. Since the late-1990s/early 2000s, a big jump in cumulative FFDI has been seen across the region. Other statistical indicators tell a similar story. The changes are particularly strong in the interior portions of NSW, with observed changes in cumulative FFDI far in excess of those predicted in the 2050 scenario already being observed over a number of years.
At this time, direct attribution of these effects to climate change cannot be made. However, the current period is very striking and no similar period has been observed in the available data. Other statistical measures support this result.
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