I came across this July 2007 report by ACTEW the Canberra based Australian Capital Territory (ACT) Government electricity and water utility. The reports title is “Water Purification Scheme for the ACT”.

My attention was drawn by ridiculous statements on climate change in the first four paragraphs of the Executive Summary. The report holds out Perth as an example of a place with “..greatly reduced long term rainfall averages..”.

Read the Executive Summary for yourself, then check my graphic below for the facts. ACTEW report Executive Summary is in italics

Executive Summary

Context and Purpose

Climate change predictions indicate that the climate would become more variable; droughts are likely to be longer and more severe, storms and flood events are likely to increase and temperatures would continue to rise. These conditions indicate that further investment in new infrastructure is required to address these changes in climate.

Since 2005, ACTEW has implemented a range of actions to increase the reliability of supply for Canberra. However, these measures would not provide sufficient water to ensure a safe, secure and sustainable water supply into the future under this more variable climate.

A significant factor to be considered is that if the recent climate is typical of the future it may be necessary to allow for worse drought events than previously considered and at worst, the possibility that we may have entered into a completely new climate pattern with greatly reduced long term rainfall averages1; as has happened in Perth and is now a real possibility here. The level of uncertainty with any prediction has greatly increased, which means that if a dam or dams are built, it may take many more years for them to fill.

Whilst such a scenario seems unlikely, it is a possibility and must be considered for future water security. Therefore, previous recommendations must be revisited and further investigations must look into options that are less reliant on rainfall. One of these options is to purify our used water.

Reference 1 from the third paragraph.

1 Even worse than assumed in previous modelling which adopted CSIRO predictions for reduced rainfall in the Canberra catchments in future due to climate change.

The rainfall index I quote for the Perth hills is an average of Mundaring PO, Karnet and Dwellingup, places which cover the extent of Perths dams down the Darling scarp.

Perth dam catchment rain for only the wet season May to October, has exceeded Queanbeyan annual rain by about 50% for the last 34 years, the Perth hills May-Oct index has averaged about 920 mm per year for the 34 years, rainfall I would have thought ACTEW would have been very glad to see fall on ACT catchments.

Let’s quickly mention Perth rain history, which is of course longer term than my Catchment Index, noting of course that Perth dam catchment rain in the Perth hills is significantly higher than Perth. Perth region rain did reduce by approximately 10% in the mid-1970’s – scroll down for my graphic and this is what the climate change proponents, such as CSIRO and ACTEW, are referring to when they say “..greatly reduced long term rainfall averages..”.

Update Thursday 30th – long term graphic comparing Perth and Queanbeyan rainfall 1871-2008

But note by the same token that Perth rain INCREASED around WWI years from previous levels not unlike the lower rain regime post the mid 1970’s. So I would say if “climate change” caused the 10% REDUCTION circa mid 1970’s, then there seems no reason why “climate change” did not cause the INCREASE in Perth rain to over a metre annual average, that took place around WWI. So in reality our long term rain history reflects cycles varying for reasons unknown, there is no evidence of a statistically significant long term reduction.

There is a long term Queanbeyan rain history here, just cyclic variations all within a band for 138 years.