This post looks at historical data for Adelaide rainfall for the period 1839 to 2018. The data comes from the BoM website and is subject to the usual caveats – there are some records missing and the presumption is made that the records are factual and not “homogenised” to fit a story.
My interest was sparked by a report some time ago that we had “the driest spring since …” so in order to put that in perspective the following analysis was done.
Leap days were removed because my rudimentary method depends on a definite number of records between 2 dates and if leap days were included then by the time the iteration had been done 130 times the dates would be wrong. There are 45 leap days in the data record of 66,082 days and they have a total of 19.6 mm of rain total so the effect is small.
Because I wanted to look at seasonal variations I decided to do it in a way where summer started on 1 December so each “year” starts in December and runs to end November the next year. In the tables you will see years labelled 1978/79 which means the “year” starts on 1 December 1978 and runs to 30 November 1979.
Rainfall totals were found for each season and tabulated along with an annual total rainfall. By some sorting the spring totals could be ranked from “driest” to “wettest”.
The table below shows spring ranked from driest at the top, 1895/96 at 33.9 mm, to the spring of 2018/09, i.e. September, October and November of 2019, at 82.2 mm. Note that this is number 30 in a list of 180 years. Adelaide’s driest spring was 124 years ago.
Interestingly, the total annual rainfall for both years was around the same.
Annual rainfall varies from 244 mm in 1958/59 to 820.6 mm in 1850/51.
The chart below shows the total annual and spring rainfall for the total data set, 1839 to 2019.
Notice that both total annual and spring rainfall vary over a wide range pretty much for the entire data record. Annual rainfall is mostly in the range 400 to 700 mm per year but fluctuations are the order of the day. There is no “trend”, just chaos. The same applies to the spring totals.
Whenever we hear of a new “meteorological record”, whether it be about temperature or rain, the vibe seems to be one where the “record” provides some legitimacy to the coming “climate change” disaster that has been imminent for around 30 years but has refused to manifest yet. Without some reference to history any story can be blown up out of all proportion and no one is the wiser.