MUNDARING WIER was only half full after Perth winter rains in 2020.
When I was young, it overflowed near the end of most winters.
My guess is massive land clearing in Western Australia combined with a bigger population using water has led to Perth dams not filling.
Land clearing of vegetation such as trees and replacement with mono-cultures and salt pans results in less evaporation to form cloud, some of which end up as rain.
Land clearing has led to desertification and climate change in Perth Western Australia.

Photo of my kids looking at Mundaring Wier in Perth's hills only half full.