Confronting our water challenge

We are, as the poet wrote, the land of drought and flooding rain. Our highly variable rainfall made agriculture, even urban existence, precarious until we built large water storages to outlast the droughts.

But today, even the massive storages we have built around our great cities are getting low. The water shortages we face today are greater than they have ever been. But our capacity to respond to them is greater too. Every Australian government is a signatory to one framework for action; the National Water Initiative. We have the resources a strong economy provides. We Australians are adaptable and innovative in meeting challenges and above all we have the sense of national purpose that is required to meet this challenge.

Our water shortages are not just a consequence of drought, exacerbated so it is plain, by climate change giving us hotter and drier seasons than those of years past.

It is because as our cities, our farms and our industry have grown so our demand for water has grown apace.

In rural Australia too we are using more water than ever. Over the last 20 years we have more than doubled the amount of surface water we take from our rivers for irrigation. In New South Wales alone, the extraction of groundwater has trebled.

Many would ask how that could have occurred. How can it be that in the lifetimes of even the youngest of this audience, during a time when the consequences of over exploitation of our waters was becoming more plain we managed to accelerate our withdrawals of water.

But let us leave the history and the blame game of over allocation to history. We are where we are. Today's task is to ensure we have the water we need for today and tomorrow.

Critics of over consumption of fresh water often describe it as a finite resource. That is a misnomer implying that the amount of water we have to deal with has known and fixed boundaries. The truth is rather different.

The amount of fresh water that is available for harvesting from the environment is not fixed at all. Rainfall, especially in Australia, can be highly variable. Moreover the amount of water which finds itself into rivers and dams or which seeps into groundwater and aquifers is dependent on many other factors including evaporation direct to the atmosphere and transpiration through vegetation.

These in turn are dependent on temperature. The hotter it is, the less rainfall will find its way into the river. In many parts of Australia, a 1 per cent decline in rainfall will cause a much larger decline in run off. This factor, known as precipitation elasticity, is why relatively modest declines in rainfall can result in big declines in dam levels.

Bushfires and the consequent regrowth reduce run off, so do forestry plantations in many areas. Indeed in that context it is worth noting that Perth has found by far its cheapest source of additional water is to clear and thin the forests in its own catchments.

Groundwater too plays a big part. Most ground water and surface water resources are connected. If we extract a megalitre from a bore the odds are, in most parts of southern Australia, that this will mean a megalitre will not find its way to a river. Yet here, as in most parts of the world, it is only recently that the interaction between ground and surface water has been understood.