Recharge of Perth’s groundwater by rainfall has fallen by up to 70 per cent over the past half-century, according to a new study led by The University of Western Australia.

Forty per cent of Perth’s drinking water is supplied by groundwater, which is also used for agriculture, private gardens and public open spaces, and is concentrated in three large aquifers which are refilled by rain in a process known as ‘recharge’. 

Researchers from UWA, the Western Australian Department of Water and Environmental Regulation (DWER) and Edith Cowan University reviewed recharge data from the Gnangara groundwater system of the Swan Coastal Plain and a new site near Gingin for their study in the Journal of Hydrology.

They found winters have become shorter since the 1960s, with fewer and weaker storms, significantly impacting recharge.

Dr Simone Gelsinari, research associate from UWA’s School of Engineering, who led the study, revealed the Gnangara system had experienced a threefold drop in recharge compared to declining rainfall, while in Perth’s endangered Banksia woodlands, recharge had fallen by up to 70 per cent.   

“Our findings suggest groundwater aquifers in climates like Perth’s are particularly vulnerable to climate change, and may see larger recharge declines, as soil needs to be saturated with rain before water trickles down to aquifer level,” Dr Gelsinari said.

“The long-term data enabled us to take a significant step forward in understanding groundwater recharge and we look forward to continuing our research with this nation-leading, collaborative monitoring network.”

Joel Hall, co-author and Principal Environmental Modeller at DWER’s Aquatic Science Branch, said understanding groundwater refill was vital to effectively manage competing demands from water users and the environment.

“Partnerships between water managers and researchers are more important than ever to help us meet this challenge in our drying climate,” Mr Hall said.

The work is part of a major initiative led by DWER’s State Groundwater Investigation Program, the ‘Recharge Estimation Collaboration/Recharge in a Changing Climate’ project, a collaboration between government, industry and academic research.

Data collected at the Gingin TERN Ecosystems Supersite, and infrastructure at the site, were funded by the Terrestrial Ecosystem Research Network (TERN), an Australian Government NCRIS-enabled project.