nature: link between agw and extreme flooding

Science journal Nature has published two papers that show links between human greenhouse gases and more intense precipitation in the northern hemisphere [1] and and also a direct link to the flooding in England and Wales in 2000 [2].

[1] http://www.nature.com/nature/journal/v470/n7334/full/nature09763.html

[2] http://www.nature.com/nature/journal/v470/n7334/full/nature09762.html

Two related articles from the Age today and yesterday:

"UK storm blamed on climate change
Geoff Strong and Lindsay Murdoch
February 18, 2011

AS AUSTRALIANS from both ends of the country were yesterday cleaning up after storms and floods, a British study has concluded for the first time that an extreme storm in that country is likely to have doubled in intensity due to human induced climate change.

The study, published yesterday in the journal Nature, is significant because for the first time climate change has been blamed for a single event.

But Australian experts are divided over whether a similar study here would have been able to blame climate change for our recent floods and cyclones, because of different factors in play in the southern hemisphere.
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The study concentrated on floods in 2000 that devastated parts of England and Wales, causing about $10 billion in damage. Researchers ran 1000 complex computer models to look at how the storms and floods were likely to have happened, both with and without the factors linked to climate change. It found that by adding in the factors the severity risk increased dramatically.

Former head of the CSIRO's Atmospheric Research Division, Dr Graeme Pearman, said that running a similar study in Australia might be able to conclude that recent events such as Queensland's floods or the intensity of cyclone Yasi were linked to global warming.

But Professor Steve Sherwood, head of atmospheric science at the University of New South Wales, doubted it would yet be provable. He said that local weather influences such as the Southern Oscillation Index, which causes the El Nino/La Nina patterns, would make it hard to pick up the influence of climate change until it became stronger.

But Dr Pearman said the British study had used different methodology to what had been used before and for the first time was able to link the climate change factors to the events.

He said the study had needed a huge amount of computing power and had been made possible by thousands of people around the world allowing researchers to access their home computers when they were not being used, to process the information. He said Australia needed to do a similar study to see if a link could be proved between our extreme weather and climate change.

Meanwhile, as residents of Melbourne's eastern suburbs were cleaning up after Wednesday afternoon's deluge, the people of Darwin were counting the cost of their most severe storm in a decade.

Darwin's authorities were warning people to stay out of flooded waterways because of crocodiles. ''Crocodiles are on the move,'' Northern Territory Chief Minister Paul Henderson said after cyclone Carlos moved inland and was downgraded.

NT Parks and Wildlife Service senior ranger Tom Nichols said there was an increased likelihood of saltwater crocodiles entering flooded creeks, rivers, stormwater drains and low-lying areas.

Despite widespread damage to streets, houses and businesses in Darwin, no serious injuries or deaths were reported as more than 600 millimetres of rain and up to 100km/h winds lashed the city over three days.

But authorities warned that the Top End would get more wild weather over the next couple of days."

http://www.theage.com.au/environment/climate-change/uk-storm-blamed-on-climate-change-20110217-1ay75.html



"Flood risk 'doubled' by greenhouse pollution
Deborah Smith, SCIENCE EDITOR
February 17, 2011

SCIENTISTS have shown for the first time that human activity has made extreme rainfall and floods around the globe worse in recent decades.

Increases in greenhouse gas emissions have also been linked, in a separate study, to a specific flood event � a devastating inundation in Britain 10 years ago.

"We found that emissions substantially increased the odds of floods occurring in ... the record wet autumn of 2000, with a likely increase in odds of about a doubling or more," said Pardeep Pall, a researcher at the University of Oxford and the lead author of the study.
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It was not possible, however, to extrapolate from this event to other ones, such as the recent Pakistan or Queensland floods, and blame global warming for their severity, the scientists said.

"It takes a long time to determine whether human influence on the climate system was a factor in any particular event," said Francis Zwiers, director of the Climate Research Division of Environment Canada in Toronto.

Dr Zwiers and his team examined daily records from 6000 weather stations in the northern hemisphere and found that between 1951 and 1999 the intensity of extreme rains and floods increased by 7 per cent.

They compared these observed changes to those predicted by climate model simulations, and identified similar patterns of intensification.

"Our research provides the first scientific evidence that human-induced greenhouse gas increases have contributed to the observed intensification of heavy precipitation events over large parts of the northern hemisphere," said a team member, Xuebin Zhang.

Although they had not studied rainfall data from the southern hemisphere, the same effect was likely to have occurred there, Dr Zwiers said.

A global change in atmospheric composition is thought to be the cause.

"Warmer air contains more moisture and leads to more extreme precipitation," he said.

Both studies are published in the journal Nature.

Autumn 2000 was the wettest in England and Wales since record-keeping began in 1766, and the floods damaged nearly 10,000 properties, with estimated losses of �1.3 billion.

Dr Pall's team generated thousands of climate model simulations of the autumn, under both realistic conditions and in a "parallel world" where no greenhouse gases had been emitted in the 20th century.

The team found that flooding risk was "substantially increased" by these emissions, although the exact magnitude of the contribution remains uncertain.

Dr Allen said scientists were developing systems they hoped would be able to quickly establish the likelihood of a particular weather event having been influenced by climate change.

This would be important for proper distribution of government resources for adaptation to climate change.

It would also makes the risks of a warming world more real to people, because extreme weather events are so damaging."

http://www.theage.com.au/environment/weather/flood-risk-doubled-by-greenhouse-pollution-20110217-1awuz.html