Acorn Mish-Mash Part 2: Scone

In Part 1 we saw that Scone in NSW has the fastest increase in 120 month mean maximum temperatures of all 112 Acorn stations.  The Station Catalogue shows a recent photo of the site with long grass at least 60cm high surrounding the screen- not a very good advertisement for compliance with siting specifications.

Fig. 1:  BOM photograph of Scone site

However the Metadata for this site reveals how much the site has changed.  Before 2005 the screen was close to the runway and a service road, and there was considerable earthworks nearby in 2001.  By April 2005 the screen had been moved to its current location.  In 2012 the grass was 60cm high as in the above photo, and was whipper-snipped during the annual inspection.  In 2015 and 2019 the grass around the instruments was “sparse” as weed control had been used i.e. it had been sprayed out with herbicide.  Temperature data for the airport may be questionable based solely on site information.

The Acorn record has been created by merging data from 01/01/1995 to 31/12/1995 from the present site at the airport with that of a Soil Conservation Research Station (SCS) 10 km away from 1965 to 1994.

Data before 1975 were adjusted downwards because of a change or repair to the screen.

Fig. 2:  Adjustments to annual data at Scone

This resulted in an increase in trend of +0.43C per 100 years.

Fig. 3:  Scone raw and Acorn annual data

However, comparison with the average of the Bureau’s nominated neighbouring stations used to make this adjustment shows the adjustment was much too great.  While the raw record from 1965 to 1973 shows Scone warming 0.29C per 100 years faster than the neighbours, the Acorn record is warming at 1.46C per 100 years- much faster than the neighbours.

Fig. 4:  Difference between Scone and average of neighbours, 1965 – 1973

While that alone is enough to cast doubt on the Acorn adjustments, an analysis of the relationship between maxima and rainfall shows that little reliance can be placed on temperature data before 1974, and after 1995.

At every well maintained site there is a relationship between maximum temperature and rainfall: periods of dry weather are hotter and periods of wet weather are cooler, because of the effects of more or less cloud cover, evaporation and transpiration.  (Wind direction will also have an influence, especially in dry seasons.)  At a well maintained station much more than half of temperature variation is due to rainfall. Therefore, if this relationship varies markedly we can deduce that either temperature or rainfall data are questionable.  This is shown by Dr Bill Johnston at his website, BomWatch, which I urge you to visit, and my analysis is loosely based on his methods.

I calculated 12 month running means of temperature and rainfall for the Airport and the Soil Conservation (SCS) sites.  Figures 5 to 7 show 12 month average temperature plotted against 12 month average rainfall for the three periods, 1965 – 1973 (in which Acorn temperatures are adjusted), 1974 – 1994 (when Acorn and raw are the same), and 1995 – 2018 (when the temperature record switches from the SCS to the airport).

Figure 5:  Scone adjusted maxima plotted against local rainfall

That is a very poor relationship: either temperature data or rainfall data are unreliable.

Figure 6:  Scone unadjusted maxima plotted against local rainfall

Here, more than half of temperature variation can be explained by rainfall.  It is not brilliant, but much better than what comes before and after.

Figure 7:  Scone Airport maxima plotted against local rainfall

While not as bad as pre-1974, less than 30% of temperature variation is explained by rainfall.  Either temperature or rainfall data, or both, are dubious.  Considering the site history and varying vegetation, this is not surprising.

It is unlikely that Acorn is a true record of temperatures at this location. Scone Acorn data are not reliable and should not be included in regional and national climate analysis.

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One Response to “Acorn Mish-Mash Part 2: Scone”

  1. billinoz Says:

    I wonder if we could ever get Phillip Adams to read this analysis ? His large organic cattle & garlic farm in the Hunter Valley is close to Scone. It might take the wind out of his Global Warming” cheer squad chanting !

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