Changes in extreme precipitation

It is a relatively bad idea to look at short term trends in rainfall – i.e reduction or increase (depending on where you are) since the 1950′s – given the multidecadal changes evident globally.

To quote realclimate – “two new papers in Nature (Min et al. 2011, Pall et al. 2011) have presented evidence that changes in the intensity of extreme precipitation since the middle of the 20th century may be linked to human induced global warming…”

Globally – much of the decadal change in rainfall arises from changes in the Pacific Ocean. Australians have been in a ‘drought dominated regime’ since the Pacific climate shift in 1976/1977 – we have since returned to a ‘flood dominated regime’ which will result in increased flooding in Australia over another 10 to 30 years. This also has impacts on rainfall in the Americas, China, India and Asia. But there are also changes in the Polar vortices which show decadal change and influence storm tracks.

So what is the Australian record – this is what the Bureau of Meteorology said about flood and drought dominated regimes in their 2010 State of the Environment Report? ‘While total rainfall on the Australian continent has been relatively stable, the geographic distribution of rainfall has changed significantly over the past 50 years. Rainfall decreased in south-west and south-east Australia, including all the major population centres, during the same period.’

Here is the trend in rainfall for 1970 to 2010 – http://www.bom.gov.au/cgi-bin/climate/change/trendmaps.cgi?map=rain&area=aus&season=0112&period=1970. There are obvious and significant declines over much of the country. The horrible consequences of a warming planet? I think not.

Here is the trend in rainfall for 1900 to 2010 – http://www.bom.gov.au/cgi-bin/climate/change/trendmaps.cgi?map=rain&area=aus&season=0112&period=1900 – and this tells a very different story.

Australians have had very little change in rainfall anywhere at all and none that could not be attributed to natural variability.

It is a invariably a matter of seeing change and attributing it to greenhouse gases. The reality is that there is natural variability – in both rainfall and temperature – and saying that something is not unnatural is very difficult indeed.

I noticed a comment on realclimate – ‘A whole bunch of big storms, floods, droughts and fires are things that can invoke the fear necessary to get action on GW. Probable attribution is so much better than where we were before.’

This also is a bad idea.

…that should be saying some event is unnatural is very difficult – as indeed was stated in the realclimate post referrd to by Mart

Filed under: In other online forums,Natural Disasters,Natural Processes — by Richard Holle @ 6:14 pm on March 10, 2011

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