The city’s growing population means a growing demand for water, but as more and more water is drawn out of Perth’s acquifers, the land is slowly subsiding

Growing demand for water in Perth has caused the city to sink at up to 6mm a year and could be responsible for an apparent acceleration in the rate of sea level rise, according to new research released by Curtin University.

The study, published in the Journal of Geophysical Research in October, found that the rate of subsidence in Perth increased between 2000 and 2005, at the same time as the Water Corporation of WA increased the amount of water it was drawing from the city’s two main aquifers to meet the demands of a growing population.

Will Featherstone, professor of geodesy at Curtin and the lead author of the study, described the effect as “like slowly letting the air out of a balloon”.

“If you take the water out of the ground, the overburden of all the rocks above pushes down,” he told Guardian Australia.

The city appears to be sinking at a rate of between 2mm and 6mm a year, variable throughout the Perth basin. The greatest change was measured at the seaside suburb of Hillarys, which has a GPS sensor to measure the rate of subsidence and a tidal marker operating side by side. Data for much of the Perth basin is patchy.

A sinking city also has ramifications for the measurement of sea levels. A few years ago the rate of sea level rise in Western Australia was reported – not entirely accurately, it turned out – to be three times greater than the global average.

As the city sinks, it is likely to mean that the tidal marker at Fremantle, about 24km south of Hillarys, is off kilter, though not by as much as 6mm. The tidal marker has been in place since 1897 and offers the longest continuous record of sea levels in the southern hemisphere. In recent years it has shown an acceleration in the rate of sea level rise. Featherstone said that flattened out, however, if you factored in the sinking landmass.

The reverse of this trend had been seen elsewhere in the world, Featherstone said. Tidal markers in Scandinavia showed the sea level was dropping, when in fact the land was rising.

“The people who use the gauges for sea level research, once they know if the gauges are subsiding or rising, can account for it in their modeling,” Featherstone said.

A properly calibrated rate of sea level rise may be cold comfort to people living in Perth’s coastal suburbs, however, if the ground continues to sink.

“If we’re seeing the rate of subsidence is 6mm per year, over 10 years that would be 6cm,” Featherstone said. “So if you have a storm surge, that’s 6cm higher than it was before.” Land that was lower also had greater rates of erosion, he said.

The Climate Council has predicted sea levels in Australia will rise by between 0.4m and 1m by the end of the century, at a cost to the country of up to $226b.

“It’s a double whammy, really,” Featherstone said.

He said the rate of subsidence had levelled out but was unlikely to reduce in the near future. Perth gets 42% of its water from groundwater, 41% from desalination and 17% from storage dams, according to the latest figures from Water Corp. As of Wednesday the city’s water storage dams were at 28.7%, the lowest level in October for eight years.

“I don’t think people in Perth are going to be willing to let their lawns go brown in summer,” Featherstone said. “And with increasing population there’s going to be increased demand for water. I don’t think we can stop the pumping.”