I noticed this article Big dry: no one knows why in the SMH this week, and in particular the claim that eastern Australia’s rainfall had dried up since the 1950′s. The report seems to be related to this press release announcing a new centre at UNSW studying climate change.
A priority for the new centre is to better understand the mystery of why Australia’s most populated region, the continent’s east coast, has suffered such major declines in rainfall in recent decades.
“We recently had a round-table of Australia’s leading climate-change researchers and this emerged as the biggest unknown issue and, of course, it seriously affects the largest concentration of people stretching right down the coast from Cairns to Melbourne,” Professor England said.
So I had a look again at the rainfall graphs and time series provided by the Bureau of Meteorology for eastern Australia and there is no doubt that we have been receiving less rainfall in recent decades than the 1950′s. However it also seems that we are receiving more rainfall than in the first half of the 20th century, so the question seems to me to be as much why did rainfall rise in the 50′s as why has in fallen in the 80′s and 90′s.
While it would be great it we could get more rainfall it seems that it is weak to link this to climate change, when it is well within the variation that we have seen over the observed history. Indeed if we look at averages they are close to the highest point they reached pre-1940. If we look at years in the bottom and highest deciles of rainfall they are right where we expect for the last 20 years (2 in the highest and 2 in the lowest deciles). If we look at percent of regions with rainfall in the lowest decile then we also see that while 2002 was high it was not the worst on record.
It seems curious to me that we should be studying climate change induced drying when we appear to be returning to the norms of relatively recent history. Now contrast this to say the below graph of mean temperature over the same region.
Now here it is clear that you may want to ask why has it become warmer, as there appears to be a clear warming trend in the last 50 years, and the recent mean values are the highest on record. I can even understand wanting to study the likely effect of warmer weather on rainfall, but the question of why has rainfall decreased seems to be a badly flawed one, as nothing we’ve seen recently in terms of rainfall seems to be beyond the normal climatic variation. Is there any reason for considering the 50′s to be more climatically typical than the 20′s, 30′s or 40′s?