Melbourne’s rainfall has abruptly fallen by an average of 107mm per year from 1997 (Chart 1).
There are still some quite wet years (2010 and 2011) and there have been very few dry years (1997 was the second driest on record. The average has just suddenly dropped.
A seven year moving average reveals the existence of rainfall cycles over Melbourne (Chart 2).
To some degree, less rainfall is an expected consequence of climate change – the sub-tropical high pressure ridge is expected to move further south towards Melbourne (the deserts extend southwards). But the change has been a downwards step change rather than a trend.
There are natural cycles in rainfall in south eastern Australia and these have played a major part in the loss of rainfall from 1996. The relative contributions of climate change and natural cycles are not clear as yet. I was able to advise the Victorian Minister for water, in 2011 during the most recent wet period, that there would be another severe drought from 2017 to 2022. That prediction, so long in advance, looks as though it was accurate.
I will provide an update in early 2020.