This page is about Perth and its (decreasing) rainfall. It is essential background for understanding our environment and the problems of gardening.
As the graph shows, we have dry summers with high evaporation but the winters are wet and rainfall exceeds evaporation for an average of 4 months. It is this excess rain during the winter months that recharges the ground water and supplies run-off to the dams.
The problems are two-fold.
(1) Especially since about 1970, rainfall has been low.
(2) We haven't had a really wet year since about 1964. It is the really wet years in which the water supplies are greatly augmented.
That is only part of the story.
CSIRO predictions based on a climate change model are that in 2030, rainfall in the southwest could be 20% lower than in 1990. Worse, by 2070 it could be as much as 60% lower.
Since the summer of 2001/2002, Perth has had fairly severe water restrictions. By mid summer, the "lawns and flower bed" gardens have loooked decidedly patchy. Restrictions are unlikely to be lifted - indeed they are more likely to be more severe.
A good reason to be more interested in native gardens.