Thursday, October 6, 2011

Flooding rains now burning plains - Bushfire risk and climate change


Grass fires and bushfires are starting already, and it is only early October - with bushfire season officially still nearly a month away. The extremely wet season Australia had at the end of 2010 and start of 2011, brought on by one of the strongest La Niña on record, has stimulated vegetation growth and is set to cause great concern as it dries and cures in the summer heat with the onset of the summer bushfire season.

Bushfire CRC | CSIRO - Climate change impacts on fire weather


According to the Bushfire CRC Firenote 86 August 2011, "The eight months from August 2010 to March 2011 were the wettest such period on record – the Australia-wide average was 715mm compared with previous high of 671mm in 1973/74. Southwest Western Australia was the only region which was drier than average."

In fact 2010 was the wettest year on record globally, with Australia experiencing it's wettest September on record, and the wettest year for Queensland resulting in disastrous floods.

Wet conditions and flooding rains to much of the continent has brought an exuberance of life and growth to central Australia. Indeed, the deserts, grasslands and scrub has come alive from the Indian ocean coast to the Pacific coast of Queensland and the Great Dividing range of New South Wales. As the grasslands and scrub dry and cure with the hot summer sun, they will become a huge fire risk in danger of ignition through stray sparks or lightning.

This summer we may see large Grass fires not experienceed in Australia for a number of decades. Grass fires may seem less dangerous than forest fires, but they can move with a rapidity and change direction quickly to take people by surprise.

It seems we have an early start to the fire season with fires being reported widely across Australia.

The Victorian CFA responded to 30 grass fires at the start of last week when temperatures reached the high 20s. In mid September 150 fires burned across Queensland which brought thick smoke haze to Brisbane and the Goldcoast.


Grass fires in the Northern Territory have already burned nearly 150,000 square kilometers in September, according to Regional Controller, Northern Territory Police Acting Commander Michael White reported by ABC news. Travellers on the Stuart Highway have been cautioned to take care driving in the smoke. On September 30, authorities were monitoring 21 large fires.

NASA have released satellite images from September 30 of the burnscar from fires in central Australia, and images of the grassfires burning in central Australia, to the northwest and southwest of Alice Springs.

For South Australia the Bushfire Cooperative Research Centre has warned that 75 per cent of the state is at increased bushfire risk because of expansive bands of wild grass according to Adelaide Now.

Fire authorities in Western Australia have initiated one of the biggest controlled burns in the history of the state on the Nullarbor plains in an attempt to pre-empt the risk of extensive wildfires this summer.

We may get some rain to dampen the fires and fire risk, but don't count on it.

One of the possible moderating factors is the development of a weak La Niña pattern which may assist with some rain to reduce fire risk and slightly moderate high summer temperatures. But a positive Indian Ocean dipole is also ocurring which may negate the rain effect of a weak La Niña. "Typically peaking in spring, and in contrast to La Niña, a positive dipole event increases the odds of dry conditions over southeastern and central Australia. In other words, this is providing a degree of counter influence on rainfall to the La Niña development in the Pacific. Sea surface temperatures surrounding Australia’s north are also average to below average, and hence not as favourable for rainfall as they were at this time in 2010. " reports the Australian Bureau of Meteorology in the ENSO wrap up dated 28 September 2011.

The long term trend for Australia climate is higher temperatures with a drying trend for the south-west and south eastern Australia. Increasing atmospheric temperatures is changing the dynamic of the sub-tropical jet stream leading to a long term trend of Less rain across southern Australia. The CSIRO has repeatedly warned that South East Australia becoming drier, with Global Warming implicated. The CSIRO and the Bureau of Meteorology issued a joint statement in March 2010 that Australia's climate already changing.

Higher temperatures and less rain will increase fire risk and fire intensity.

The trend for the future is an increase in the number of days with very high and extreme fire-weather. At an increase of 1 degree C in average global temperature the percentage increase in 2020 for Very High fire danger days will be +10-30% and for Extreme Fire danger days will be +15-65%. By 2050 with an average global temperature of 2.9 degrees C the perectage increase for Very High danger days will be +20-100% and for Extreme days +100-300% (Lucas, C., K. Hennessy, G. Mills and J. Bathols, 2007: Bushfire weather in southeast Australia: Recent trends and projected climate change impacts)

Christopher Lucas, in a 2009 paper on Climate Change Impacts on Fire weather (PDF) explains the trend:
"Fire weather is clearly changing across Australia, with a tendency towards more dangerous conditions being observed across the country. Significant trends in median and 90th percentile FFDI are observed in all seasons, but overall, it is the summer months – the peak of the southern fire season-- that shows the least amount of change. The largest changes are occurring in the spring and autumn, broadly consistent with the model projections. The fire season is lengthening, with an earlier start and a later end. The number of ‘extreme’ fire weather days is increasing in spring, summer and autumn. In a regional sense, the Murray-Darling Basin region is seeing the biggest change in fire weather danger, with significant positive trends observed in all four seasons. In general, the eastern portion of Australia is seeing larger trends in more seasons, but almost every region shows some degree of change."

Lucas concludes by saying the possibility of interdecadal variability cannot be ruled out and that "a direct attribution to anthropogenic climate change cannot be made at this time."

In 2009 Australia experienced one of it's worst natural disaters with the death of 173 people in the Victorian Black Saturday bushfires. David Karoly, Professor of Meteorology at the University of Melbourne in Australia, explained the connections between climate change and the catastrophic bushfires in an article a week after the fires - Bushfires and extreme heat in south-east Australia - published on Realclimate.org.

We may need to learn to live and adapt to the increasing bushfire risk that is posed by climate change. The less action we take now to reduce carbon emissions and global warming, the more risk we will face in the future with a greater number of extreme fire weather days and bushfires burning with greater intensity.

Sources for images
* Bushfire CRC
* NASA Earth Observatory