Friday, February 13, 2009

Record rain in Bourke, floods to hit

A record 200mm of rain has fallen in Bourke as the top end of NSW prepares for floods.

The weather bureau has issued a flood watch and a severe weather warning for the area, just days after flooding claimed lives and forced dozens of evacuations in Queensland.

Heavy falls are expected to continue over the central north of NSW on Saturday, followed by a deluge over the mid-north coast.

Bourke experienced the brunt of the storm conditions on Friday night with more than 200mm falling, causing flash flooding in the district, a State Emergency Service spokeswoman said.

But half of the calls made to the emergency service were from people in Sydney's metropolitan area, she said.

"We've had approximately 40 requests for assistance across the state," the spokeswoman told AAP.

"Approximately 20 of those came from the Sydney metropolitan area - they were related to trees down."

There were no injuries reported and no threats to property, but the worst is still to come, she said.

Heavy rain was expected to hit towns such as Walgett, while further south, Tamworth and Inverell could also be affected, the manager of the Bureau of Meteorology's Flood Warning Centre Gordon McKay said.

Heavy rain was also expected on Saturday and Sunday on the mid-north and north coasts, with the area between Coffs Harbour and Kempsey likely to see falls of 150-200mm.

"We expect over the weekend a low pressure cell to develop off the coast of northern NSW, and that's likely to lead to very heavy rainfalls," Mr McKay said.

Update Mon 16/2/09 from the Sydney Morning Herald lah...............

The heavy weather has also hit some parts of the state inland. Drought-ravaged Bourke woke on Saturday morning to find itself knee-deep in water.

Residents said a thunderstorm dropping hailstones as large as golf balls had swept in on Friday evening, followed by rain that did not let up for 12 hours.

The town got 200 millimetres of rain overnight - a third of its annual rainfall, and the biggest single fall any of the residents could remember.

"I think the previous record was about five inches [125 millimetres] in one go but this has well and truly superseded this " said a local SES controller, Stephen Walsh.

The mayor, Andrew Lewis, said it was a "one-in-120-year event".

Jonathan Roe, a reporter for the The Western Herald, said some children were swimming in the streets on Saturday morning. Other residents were out in their cars touring the flooded areas, and marvelling at the sight of parts of the town submerged.

The rain cut several major highways out of town and paradoxically left residents short of drinking water. Flooding had overwhelmed the pumps that extract the town water supply from the Darling River.

The SES was still working late yesterday to clear water from 25 houses.

Farmers had mixed responses to the downpour.

A cotton grower, Ian Cole, said some of his neighbours had suffered heavy damage to cotton crops, particularly from hail. Another reported that his 1500 sheep were now having to be extracted from " black mud".

But generally graziers were happy as the rain would mean good winter grasses for stock and a "flushing out" of the Upper Darling all the way down to the Menindee Lakes.

The weather left Bourke residents scratching their heads about what would come next.

"Floods up north, and bushfires in Victoria, and here we are in a massive drought and we get two-thirds of our annual rainfall in 12 hours," Mr Walsh said. "We hope we're not going to go without for the next 12 months."

The end of certainty

All signs point to the climate becoming more extreme, write Marian Wilkinson and Ben Cubby.

When hundreds of small, grey-headed flying foxes began falling from the sky at Yarra Bend in suburban Melbourne, for some it heralded the awful events that would later unfold. It was Wednesday, January 28, one day into the ferocious heatwave that would wax and wane before returning with terrible intensity last weekend.

That first day, calls began pouring into Wildlife Victoria. As the bats were dying en masse in the city, ringtail possums were falling out of trees in the bush and distressed kangaroos, too weak to jump, were baulking at fences.

"It was just unbelievable," said Fiona Corke, a Wildlife Victoria rescuer. "The animals were behaving very strangely. We were telling people to leave dishes of water by the side of the roads."

By January 30, Melbourne's temperature topped 45.1 degrees. A climate scientist, Dr David Karoly, noticed the city's plane trees had begun to shed their leaves under the stress of the heat.

In Tasmania, half the state recorded its hottest day on record. Launceston Airport hit 39.9 degrees, well over two degrees higher than its last record temperature.

In Adelaide, in the early hours of January 29, the city experienced its hottest night on record, 33.9 degrees.

Just north of the city, the air base at RAAF Edinburgh recorded an extraordinary 41.7 degrees at 3am. "Such an event appears to be without known precedent in southern Australia," the Bureau of Meteorology said.

People began turning up in the public hospitals, felled by the heat. As the days wore on and on, heat-related hospital admissions would ultimately reach more than 700.

To climate scientists and professional forecasters, it was clear that Australia was experiencing "an extreme weather event". But few among the public realised at the time, these first awful days would be just phase one of the heatwave.

As the weather bureau would later report: "After a slight drop in temperature during the first few days of February, extreme heat returned to the south-east on February 6. Temperatures rose sharply in South Australia and western Victoria on the 6th but it was the 7th which saw the most exceptional heat of the whole event."

As the nation reels from the toll in the bushfires, climate scientists are trying to carefully assess what lessons can be learnt from the unprecedented heatwave of 2009 and the deadly fires that accompanied it.

While state authorities focus on the crucial investigations into arson, emergency advice, town planning and tree clearing, looming over all these is what role human-induced climate change is playing in Australia's weather patterns. And, critically, how much of country will become more at risk from bushfire because of climate change?

The Victorian Premier, John Brumby, bluntly acknowledged this week that climate change cannot be ignored in the future debate over the bushfires.

"There is clear evidence now that the climate is becoming more extreme," Brumby told The 7.30 Report. And, announcing a royal commission on Australia's worst natural disaster, he insisted it would look at all aspects of the events. "I want everything on the table."

On the day the bushfires started claiming lives, Melbourne reached a record 46.4 degrees for the first time in 154 years of record-keeping, overshooting the high set on Black Friday, January 13, 1939 by 0.8 degrees and far exceeding the temperature on Ash Wednesday in 1983.

Climate scientists who spoke to the Herald this week repeatedly stressed that, despite these extraordinary temperatures, one extreme weather event cannot be taken as evidence of climate change.

But nearly all made the following points. Australia has experienced a general warming trend over the past 50 years which is consistent with human-induced climate change. The south-east of Australia is also experiencing a long period of unusually dry weather which may also be related to climate change.

Both these trends will increase the number of days where the bushfire risk will be more extreme and bushfires will be more intense. Most importantly, unless global greenhouse gas emissions are curbed, these trends will get worse over the next decades.

"The projections are based on climate models which include increases in greenhouse gases and that tells us that we can expect higher temperatures and much drier conditions over southern Australia," a CSIRO bushfire researcher, Kevin Hennessy, told the Herald.

"They are two of the critical elements that are needed to create a fire. The other two are low humidity and high wind speeds. Not only are we estimating there will be an increase in the frequency of extreme fire danger days but the duration of the fire season will be longer and the intensity of some of the biggest fires may increase."

Mr Hennessy co-authored a landmark report on the increased risk of fire weather due to climate change in 2007 which was cited in the Garnaut Climate Change Review. The study defined two new categories of fire weather - "very extreme" and "catastrophic". Under a "no mitigation scenario", in which no action is taken to reduce greenhouse gas emissions, there would be between five and 25 more days each year when Australians face extreme fire dangers by 2013, compared to the baseline year of 1990.

And the threat would rise quickly. By 2030, it may rise to between 15 and 65 days a year. In 2067, when Australia's average temperature may be 2.9 degrees hotter than in 1990, there would be between 100 to 300 days of extreme fire danger each year. "This effect increases over time but should be directly observable by 2020," the report noted.

The soaring heatwave temperatures last weekend, while unprecedented, are consistent with a general warming trend as a result of growing global greenhouse gas emissions. The 1990s were the warmest decade ever recorded instrumentally, and the last 100 years were the warmest of the millennium.

In 2007, Victoria recorded its warmest year on record, 1.2 degrees above the average. In the decade before, it experienced its driest years on record. Then, briefly, the end of 2007 promised relief. It was supposed to be a cooling, "La Nina" year. Rain fell in spring last year and temperatures dropped, but this summer hopes were dashed. From January 4 to February 7, virtually no rain fell in Melbourne, "equal to the second-longest dry spell on record for the city", according to the Bureau of Meteorology.

The mighty forces determining Australia's climate are complex and only partly understood, but research published in the past month has added significantly to the stock of knowledge. It also overturns some of the popular understanding of the "La Nina" influence.

The University of NSW research showed that the Indian Ocean Dipole, a swirling current that circulates warm water off Australia's north-west coast, appears to have a major influence on our weather and can override La Nina.

Dr Caroline Ummenhofer and Professor Matthew England at the university's Climate Change Research Centre showed that when "positive" dipole cycles send unusually hot, dry winds down to south-east Australia, drought is often the result. The big dry that straddled the start of the 20th century and ruined thousands of outback pioneers corresponded to a positive dipole, and so did the drought that spanned World War II.

The severe drought across southern Australia, the backdrop to this week's fires, has been accompanied by a run of three positive dipoles. The researchers believe this is why the La Nina event in the Pacific in 2007-08, which traditionally brings rain, was unable to break the drought. Three consecutive positive cycles is unprecedented, Ummenhofer said. Whether this is linked to human-induced climate change needs further investigation, the researchers say. And the El Nino-La Nina cycle of warm and cool atmospheric phenomena in the Pacific will still have a major influence over Australia's climate, even though not as much as previously thought.

Another, separate force driving weather patterns in southern Australia is the haze of air pollution over Asia. The aerosol haze, a stew of industrial output, fires, exhaust fumes, dust and plankton respiration, cools Asia, acting like a shield for the sun's heat and keeping much of Asia a degree or two cooler than it would otherwise be. This can actively force changes in wind and ocean currents by changing the distribution of solar heat on the Earth's surface, said the lead researcher, Dr Leon Rotstayn, of the CSIRO's Marine and Atmospheric team.

The aerosol haze forces more heat into the monsoon winds which douse Australia's north-west. But it also contributes to a build-up of high pressure which may contribute to less rainfall across southern Australia, according to new research released by the CSIRO and the Bureau of Meteorology.

Human-induced climate change, while separate to these overlapping forces, has the power to exacerbate them. CSIRO's Dr Penny Whetton says the long-term trend in Australia includes about 0.9 of a degree warming through the 20th century. Australia is looking at a warming of about 1 degree by 2030 and 1.5 to 4-5 degrees by 2070 unless greenhouse gas emissions are reduced.

"You can't say we expected a 46 degree day in Melbourne this year but we would expect that it is getting increasingly easy to set new records compared to the past because of the underlying warming trend that's occurring," Whetton said.

The causes for the big dry over southern Australia are, she says, more complicated.

"The drying trend over the last 10 to 12 years is consistent with the rainfall change we are projecting using climate models. It's actually a more severe decrease than the models are projecting. At the moment it's too early to say whether its climate change-related. In all likelihood it's some combination of some influences of long-term climate change and natural fluctuations of the climate system."

Whatever the immediate causes of the bushfires, for many Australians it is a reminder of the potential risks of uncontrolled climate change.

As the Climate Change Minister, Penny Wong, put it last year,"As one of the hottest and driest continents on earth, Australia's economy and environment will be one of the hardest and fastest hit by climate change if we don't act now."