Climate Change and Rainfall

Mr Gunter makes some good points in his letter concerning rainfall in The Narooma News 10/2/10. He says there is nothing unusual about the current dry period. He implies that it is not possible to blame current rainfall patterns on climate change. I disagree with his first point, but agree with the second.

When looking at Bureau of Meteorology rainfall figures for Bega, it has never been this dry. Mr Gunter tells me that the drought from 1938-1946 was just as bad. Over those 9 years, the average rainfall was 630 mm/year. Compare that with the last 15 years from 1995-2009. Over those 15 years average rainfall has been 567 mm/year. It would seem to me that the current drought has been more intense and has gone on for longer than the previously worst drought of the early 40s. Not only that, but the last 10 years have been hotter than the 40s (2009 was the hottest year ever recorded for NSW). By any measure, the current drought is unprecedented if you look at the BOM figures for Bega. I accept that rainfall figures for the coastal fringe have not seen the same level of drought.

I think this discussion highlights the difficulty of trying to determine a rainfall trend when that rainfall is subject to natural variation, and is sporadic at the best of times. Recent heavy rainfall illustrates that point. Could this be the end of 15 dry years? It is a huge relief to see the dams and rivers full again.

I think it will be many years, or even decades before we can detect a significant rainfall trend, and until that time it is not be possible to blame droughts in SE NSW on climate change. I am sure that Mr Gunter and I agree on that point.
At a national level the Bureau of Meteorolgy has determined 4 trends;
• There has been a significant reduction in winter rainfall in south-west Western Australia since the 1970s.
• Rainfall has decreased substantially since 1950 on the east coast, and in Victoria. This decline is less marked if measured from 1900.
• The last decade has seen very low rainfall in southern and central Victoria
• Rainfall in north-west Australia has increased substantially since 1950.

The current drought in the Bega Valley (excluding the coastal strip) is unprecedented, but now hopefully over. To say that the drought is due to climate change is presumptive. To say that the impact of climate change is not worth considering is short sighted.
Matthew Nott