Better groundwater knowledge needed as climate changes

One-third of Australian taps deliver groundwater for our daily use.

On the world’s driest inhabited continent, 70% of land is either arid or semi-arid, so it should come as no surprise that 17% of water sources accessible to our regions are from under the ground.

In the 40 years to 2015-16, the use of groundwater in Australia almost doubled to more than 5GL per year. 70% of that was for agriculture or pastoral purposes – mostly irrigation – with the remainder for mining, and domestic and town supplies. 

What is a surprise, however, is that the quality, quantity and management of Australian groundwaters remain, generally speaking, poorly understood and documented. 

We know, for instance, that many aquifers had limited recharge after the millennium drought. Yet many areas of Australia are also short of basic groundwater data, a situation as true globally as it is here at home. This is despite a 2010 study finding 80% of the world’s population faces high threats to water security.

Perth and its regional environs, where groundwater contributes 70% of local supplies, might be an exception to this grim summation. Recent research and climate change policy responses are perhaps more progressive than elsewhere.

Cosmos reported in March 2023 that a recent review of groundwater management across Australia had found substantial gaps in its “technical tools, implementation, and fundamental understanding”.

Published in the Journal of Hydrology, the review prompted contributing scientists to call for an urgent and better appraisal of groundwater and how we manage it.

The report roughly coincided with the publication of a global review of groundwater that concluded it “plays a critical role in resilience, as it buffers spatiotemporal variability in surface water”.

At the same time, the study reported that aquifers were “far more difficult to manage on a large-scale basis than surface water”, rendering them more susceptible to overexploitation. 

Given one resource feeds the other, the researchers urged water managers to consider groundwater together with surface water, as a single resource. For example, “excess surface water during wet periods can be temporally reallocated by storing water in depleted aquifers for use during dry periods”. 

Understanding groundwater to achieve sustainable management

The first of two recent studies of groundwater and how we are faring under climate change was published in Water Resources Research in November 2023. It examines how sensitive groundwater levels are to variations in meteorology across Australia.

Researcher and lead author dr xinyang fan.
Researcher Dr Xinyang Fan, lead author of a new study into the relationship between groundwater and meteorology.

Studying this relationship explicitly is rare, writes University of Bern postdoc and lead author Dr Xinyang Fan. So many factors are at play, such as groundwater pumping and land use change. 

Nevertheless, understanding such basic sensitivities is “pivotal to managing groundwater sustainably”.

The team tracked how groundwater responds to differing meteorology across Australia by using long-term bore records, but only from sites where climate variation dominated groundwater behaviour, enabling the ruling out of other factors.

The results found that the median groundwater level changes by 42mm nationally – and the recharge changes by 0.43mm – with every 1mm change in precipitation.

Dr rebecca doble
CSIRO senior research scientist Dr Rebecca Doble led a team that investigated how groundwater in the Murray Darling Basin was responding to climate change.

In a second recent groundwater study, published in the Hydrogeology Journal in October 2023, CSIRO senior research scientist Dr Rebecca Doble led a team investigating how groundwater in the Murray Darling Basin was responding to a changing climate.

The Murray Darling Basin is highly allocated and regulated, a water system where complicating factors are many and varied.

Larger than France and Spain combined, most of the basin’s rivers start in the Great Dividing Range in Queensland. The basin ends in South Australia where the Murray River meets the Southern Ocean.

Current forecasts for how climate change may affect the massive drainage system suggest arid and semi-arid zones will expand to replace currently temperate areas.

The researchers report that already there has been “a decline in groundwater levels” as well as “changes in the connection status between rivers and groundwater”.

The modelling of Murray Darling Basin systems predicted a further reduction in groundwater recharge in the future and an ongoing decline in groundwater levels.

The Greenlight Project is a year-long look at how regional Australia is preparing for and adapting to climate change.

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