Dr David Jones, the head of climate analysis at the Australian Bureau of Meteorology, in an opinion piece, ‘Our hot, dry future’ has argued that over the past 11 years Melbourne’s rainfall has been about 20% below the long-term average experienced declining rainfall over the past 11 years .
In response, Dr Jennifer Marohasy posted ‘How Melbourne’s Climate Has Changed: A reply to Dr David Jones (Part 3)’, which included a graph of high quality data of rainfall at Yan Yean, Victoria, because of its proximity to Melbourne.
The graph is from Mr Warwick Hughes based on Bureau of Meteorology data and shows that recent rainfall decline at Yan Yean is comparable to declines during previous droughts.
I have also graphed Bureau data for some of Melbourne’s catchment areas. While I couldn’t find a site with data extending back as far as the Yan Yean site, the Maroondah and O’Shanneyssy stations show a significant recent decline in rainfall that is greater than previous droughts in the 1896, 1925 and 1945.
Some of the Melbourne catchment areas rainfall data shows recent significant decline, but there are a number of problems with using bureau rainfall data for the Melbourne catchment. A main problem is that the Bureau does not have rainfall data for Melbourne’s largest reservoirs, Upper Yarra and Thomson back more than 30 years.
The best publicly available data on catchment area rainfall comes from Melbourne Water. However, Melbourne Water’s publicly available data is only from 1998 to 2008.
Without long-term high quality data of catchment area rainfall for all catchment areas, it is impossible to know whether the longer-term trend shows dramatic declines at many, or just some, places in the Melbourne catchment.
Blue Mountains, Australia