Water planning 101: stabilise the population

It should be strong sustainability, "to prevent further loss of natural habitats and ecosystem functions".

Stretched water resources

Half of Australia gets less than 30 cm of rain annually. We've much more variable rainfall and runoff than other continents. This century, average rainfalls have diminished, in the well-populated south-east and south-west.

Easily our biggest water-user is agriculture. Though population has doubled since 1977, remarkably, aggregate water use is said to have "slightly reduced".

Victory laps for irrigators and planners, eh? Problem is, we've hit the wall.

Household water-use efficiency has barely improved since 2010. Our top six cities still get nearly 60% of their take from surface water. But groundwater (25%) is increasingly stressed and over-allocated, with heavier reliance on desal (12%).

The indirect water-consumption "footprints" of eastern-seaboard cities are 8-10 times higher than what they use directly. If you doubled their present populations, MDB would struggle to feed them. At affordable prices, that is.

Climate and water supply

Australia's trending hotter and drier, 2019 being the driest year on record. Inflows into west-coast dams and east-coast Murray River are declining. Extreme heat – and rain - events are increasing.

"Droughts, flood, and bushfires" damage soil, vegetation, and catchment water-quality. With few viable sites left, building extra dams won't cut it. Many regional towns have already experienced severe water shortages.

Comparing with our 2000-year paleoclimates, the 20^th Century looks "wettish" and Millennium Drought "moderate". Australia endured mega-droughts, in these paleo times. Urban-rural water planning should take heed.

Increasing desal dependence

By 2000, urban water-demand had reached the maximum that could be "reliably" supplied by "conventional" rainwater and groundwater. Significantly, no city deployed desal.

Now, we've six plants in five states. Perth's particularly reliant on desal and groundwater.

Studies over 2010-16 found desal might be "better" than extra dams as a "long" term option. They didn't factor in population growth.