Geoscience Reference
In-Depth Information
(A1B) emission scenario (Leslie et al., 2008). The central year is close to 2030,
which corresponds to a global warming of 0.54-1.44°C (CSIRO and BoM,
2007). The average return periods for large and giant hail decrease by almost 50
per cent, i.e. the frequency almost doubles. For example, hail greater than 6cm in
diameter that currently occurs once in eight years occurs once in five years during
1991-2050, and hail greater than 10cm that currently occurs once in fifty-one
years occurs once in 28 years during 1991-2050.
Extreme wind
Projected changes in extreme daily wind-speeds (defined as the highest 1 per
cent) from 19 climate models were analyzed by McInnes et al. (2011) for the
medium (A1B) emissions scenario for 2081-2100 relative to 1981-2000. The
associated global warming in this scenario (
Table 3.3
), is slightly less than
1.7-4.4°C (the IPCC [2007] range of warming for A1B emissions in 2090-99
relative to 1980-1999).
Over northern and central Australia, at least two-thirds of the models agree on
small changes within
2 per cent. Over southern and eastern Australia, there is
a tendency for weaker extreme wind speeds, which is most pronounced in June
to August.
Extreme fire weather
Over southern and eastern Australia, warmer and drier conditions are expected
in future (CSIRO and BoM, 2007). Consequently, an increase in fire weather risk
is likely, with more days of extreme risk and a longer fire season.
The annual average number of extreme fire weather days at 26 climate stations
in south-eastern Australia was estimated by Lucas et al. (2007) for the current
climate (1973-2007), using the Forest Fire Danger index (FFDI). Projected
changes in daily temperature, humidity, wind and rainfall were generated from
two climate simulations named CCAM (Mark 2) and CCAM (Mark 3) for
the years 2020 and 2050, relative to 1990, for low (B1) and very high (A1FI)
emission scenarios. These changes were applied to observed daily data at each
climate station, and FFDI values were re-calculated. The number of extreme
fire danger days generally increases 100-300 per cent by 2050 for the very high
emissions scenario (
Table 3.3
). The global warming in 2050 for the very high
scenario is 2.9°C (CSIRO and BoM, 2007).
Output from the CSIRO Mark 2 climate model was also downscaled at 56km
resolution over Australia (using the Regional Atmospheric Modelling System:
RAMS) for low (B2) and high (A2) emissions scenarios in 2050 and 2100
(Pitman et al., 2007). Under the high (A2) scenario in 2100, there is a 50 per
cent increase in the January mean forest fire danger index (FFDI) over most of
the continent.
It should be noted that projected changes to fire weather cannot be directly
translated to changes in actual bushfires. The change in future fire activity is
