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Cabramurra : what happened in 1996?

An automatic weather station (AWS) in a small Stevenson screen replaced the previous liquid-in-glass and larger thermometer shelter at the Cabramurra ACORN weather station on 10 December 1996.

small stevenson screen at cabrumurra

See ACORN Observation Practices (p13)

As evident in the maximum and minimum temperature charts below, there was a significant and abrupt warming at the Cabramurra weather station starting at the end of 1996.

cabramurra maximum temperature trend

cabramurra minimum temperature trend

The table below shows maximum and minimum temperatures in the 10 years before and 10 years after 1996 (AWS and small Stevenson screen December 1996) as estimated in the homogenised ACORN 1 and ACORN 2 temperature datasets, and the unadjusted original RAW observations :

cabramurra maximum and minimum temperatures

Note: 1997 and 1998, marked above, use the original Cabramurra 72091 weather station annual temperatures in the RAW column whereas ACORN uses the new Cabramurra 72161 automatic weather station temperatures in 1997 and 1998 (see below). The 1997-2006 average RAW maxima and minima above are based on 1997 and 1998 at the new AWS.

The 1987-1996 maximum averages were : ACORN 1 10.98C / ACORN 2 11.44C / RAW 11.48C

The 1997-2006 maximum averages were : ACORN 1 12.55C / ACORN 2 12.55C / RAW 12.55C

The 1987-1996 minimum averages were : ACORN 1 4.18C / ACORN 2 4.55C / RAW 3.92C

The 1997-2006 minimum averages were : ACORN 1 5.03C / ACORN 2 5.02C / RAW 5.02C

The original RAW maximum averages increased 1.07C from 1987-1996 to 1997-2006, the jump clearly starting at the end of 1996.

The ACORN 1 maximum averages increased 1.57C from 1987-1996 to 1997-2006, an even greater increase because of maxima cooling in 1987-1996.

The ACORN 2 maximum averages increased 1.11C from 1987-1996 to 1997-2006, with ACORN 2 cooling 1997-2006 by 0.12C - potentially to compensate for the 1.07C increase that coincided with the installation of an AWS with a small Stevenson screen.

The original RAW minimum averages increased 1.10C from 1987-1996 to 1997-2006, the jump clearly starting at the end of 1996.

The ACORN 1 minimum averages increased 0.85C from 1987-1996 to 1997-2006, due to a 0.26C warming of 1987-1996 and a 0.7C warming of 1996-2007.

The ACORN 2 minimum averages increased 0.47C from 1987-1996 to 1997-2006, with ACORN 2 warming 1987-1996 by 0.63C and warming 1997-2006 by 0.6C.

The BoM's ACORN-SAT station catalogue reads :

The current site (72161) is an automatic weather station, over short grass on top of an open high point about 300 m southwest of the Cabramurra township. This is a very exposed location, with slopes dropping several hundred metres in all directions except the northeast quadrant. To the northeast, the ground drops to a saddle in the town area before rising again towards the main Snowy Mountains range.


The original site (72091) was about 400 m east of the township on top of a west-facing spur near the turnoff into the town from the Kiandra-Khancoban road. Data are available from this location since 1962, although there is evidence that observations may have been made from 1954 onwards. There are no indications of any moves at this site during its history, although there were more buildings in the vicinity in the 1950s and 1960s than there are now. The site continued temperature observations until April 1999.

The automatic weather station (72161) is located 600 m west of the previous site and has been operating since 1996.

There was a significant Cabramurra rainfall decline from 1987-1996 to 1997-2006 (annual average 1,874.1mm > 1,185.6mm), but the 1997-1998 overlap of Cabramurra 72091 and 72161 temperatures in the table above show that the original 72091 station recorded maxima about 0.6C warmer than the 72161 AWS, and about 0.30C cooler minima.

Despite this, in the 10 years before and after December 1996, average maxima increase 1.19C (or 1.79C including the 0.6C cooler new location) and average minima increase 1.04C (or 0.74 including the 0.3C warmer new location).

The data above show a clear minimum and maximum increase as soon as the AWS and small Stevenson screen were installed, confirmed by ACORN adjustments that react immediately but inadequately to the change in shelter size and from a liquid-in-glass thermometer to an AWS with one second temperature readings.

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