The current flooding of large parts of Australia has thrown the spotlight on what is probably our greatest, most precious and yet poorly understood resource: groundwater.
As the climate warms and our population grows, groundwater will become a major determinant of Australia's future. How well we manage it will define the prospects of many of our cities and towns, their industries and jobs, our landscape and our economy. As a resource, groundwater probably holds more significance for our long-term national destiny than gold, iron ore or coal.
Globally, groundwater is a vast resource, comprising 97 per cent of the fresh water on Earth and providing around 40 per cent of humanity's total water needs. In Australia it supplies about 20 to 30 per cent of our water use, for activities such as agriculture, mining, manufacturing and for domestic use in cities like Perth, Newcastle and Alice Springs.
However, climate change is likely to make groundwater increasingly important in the future, as surface supplies become more stressed due to higher evaporation, rainfall variability, population growth, and the competing requirements of industry, agriculture and the native landscape. Our population is forecast to grow to between 31 and 42 million by the mid-century, especially our urban population and this, in turn, will lead to a huge increase - possibly a doubling - in demand for fresh water. Even with desalination and recycling, groundwater will be a critical element in how we meet this demand.
Australia is a dry continent without glaciers, permanent snowfields or large and abundant permanent lakes, where evaporation generally exceeds rainfall across most of the land surface. This makes water stored underground of even greater strategic significance to our future national security than it is in other countries.
All the more reason, then, for us to understand far better the nature of this largely unseen resource - its extent, volume and the rates at which it is recharged.
Traditionally groundwater has been regarded as a fallback in Australia, a resource to be tapped at will whenever surface water became unreliable. Traditionally too, we have tended to treat it as inexhaustible - despite plentiful evidence to the contrary. In the Great Artesian Basin, for example, water tables began to decline within a few years of the first bores being sunk, and it has since been demonstrated that some of the basin waters are very old - hundreds of thousands of years. This gives vital clues to just how slowly groundwater moves, its recharge rates, the large residence times in this big basin and that it was largely recharged in ancient, wetter climates.
Groundwater is like a bank account: to manage the budget you need to know how much you are earning (in groundwater terms, the rate of recharge) and how much you are spending (which in water is the rate at which you extract it). The difficulty lies in the fact that groundwater is out of sight, if not out of mind, and can be very difficult to measure with precision.
This issue lies at the heart of the current national debates over the Murray-Darling Basin Plan and coal-seam gas. Neither can be satisfactorily nor equitably resolved without a fuller understanding of groundwater, its extent, age, recharge and extraction rates, and its impact on other resources, communities and industries. Even then, uncertainties will remain which must be allowed for and explained to an increasingly concerned public.
There is a clear need to highlight what we do know and not just what we do not know in an informed and balanced debate, underpinned by data, facts, as well as lessons learned from our own and other international experiences. Raising awareness, myth busting and increasing transparency are critical in improving public trust and confidence in important groundwater issues. While, in theory, every bore in Australia should be licensed and monitored, it is believed that there are thousands of illegal bores - some of them historical, but many quite recent. It is a fact that whenever there is a drought and surface water runs low, the first thing many people do is sink a new well. This lack of control underscores the difficulty in regulating and enforcing responsible groundwater management in Australia.
Groundwater is connected to surface rivers, lakes and wetlands, and its extraction causes all these to shrink, as well as water tables to fall. When the water table sinks below the reach of the roots of Australian trees and shrubs, landscapes can perish - as has occurred in some of the river red gum forests and wetlands of the Murray-Darling.
Coal-seam gas extraction requires coal beds to be depressurised by bringing large volumes of gas and water to the surface, and the current wave of gas development may involve the extraction of large amounts of groundwater. There is much work still to do to better understand important environmental, regulatory and economic issues associated with coal-seam gas production.
There are many positive groundwater news stories. Australian scientists working in Adelaide, the Bowen Basin in Queensland and around Perth, have demonstrated great scope to store surplus surface water - such as city runoff - in aquifers underground, where the water undergoes a natural cleansing process.
As the recent downpours have reminded us, Australia is a land of drought and flooding rains - and if current climate predictions prove accurate, droughts could become more frequent and intense in future, as may rainfall in some areas. As our population grows its demands for water for agriculture, industry, mining, amenity and the environment will soar.
We need to start thinking now about how we will meet those water requirements in future. We need to plan how we can save surplus water in times of plenty for times of scarcity - as groundwater. The central issue in effective groundwater management is trust. We need to be able to rely upon the integrity of the data and projections of our hidden water resource, and the institutions which supply them. This is highlighted by the present debate, which is distorted by much misinformation, emotion and wild guesses.
We also need national coordination and oversight of groundwater, as the basis of sound policy whether federal, state or local. Given these, Australia can well play a role as a world leader in planning the future of one of humanity's most precious resources - and reap the rewards in the century of resource scarcity. And we can bank our current floods for a dry future.
Craig Simmons is director of the National Centre for Groundwater Research and Training and Professor of Hydrogeology at Flinders University.