Water Planning- A Long Term View

No doubt about it, much of WA is a dry place. We hear and read lots about climate change and how it is affecting our water supply. Two years ago we had an almost endless flow of messages about 'the worst drought on record' and stuff like that. As it turned out Perth was fairly dry that year, with 703 mm, while the north of the State had it's eighth wettest year ever. The capital cities of South and Eastern Australia were dry, while Australia as a whole had a slightly above- average annual rainfall. Hardly the disaster that was painted in the media.

The real issues are that our rainfall is highly variable, we don't have geography that allows many big dams (Australia is flat) and, most importantly, we continue to use more and more water. Perth is growing fast. 

Here's a plot of annual rainfall in Perth over the last hundred years, since 1876. It shows that we are getting less rainfall than we did in the 1940s, and a bit more than we got at the beginning of last century. It certainly does not show any long- term decrease in rainfall. (Click on the plot to enlarge it.)

Perth RainfallDry years, and wetter years, are quite common (the plot zigs up and down a lot). By the way, Perth's average rainfall is  790 mm a year. Melbourne gets less, with 650 and Adelaide much less, with 520.

The other part of a discussion of water supply is the rate that we use the stuff. In 1979 we used 130 gigalitres in Perth. In 2005 we used about 230 gigalitres (up 77%). The city is growing, fast.

Although we are doing well at reducing our individual consumption, there are lots more of us here. Population growth exceeds our rate of improvements in water use. We'll just have to get even better at being Water Wise.

Some useful links are WA State of the Environment 2007, Perth Water Users Group, Rainfall History

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