Sunset over Sydney Harbour. Picture: Noel Kessel Source: The Daily Telegraph

Scientists from the CSIRO in Hobart and the Lawrence Livermore National Laboratory in California have used the most accurate study yet of ocean saltiness to show the world’s dry areas, like Australia, are getting drier and its wet areas getting wetter.

And it’s happening at an alarming rate.

“It’s this idea that the rich get richer, so the high rainfall areas will become more rainy, and the low rainfall areas will become drier,” says research oceanographer Dr Susan Wijffels, co-author of a new paper which appears in the journal Science.

“We see that reflected in the (oceans’) surface salinity field where the salty areas are getting saltier and the fresh areas are getting fresher.”

The scientific team says the rate at which the atmosphere moves water from dry spots to wet spots increased by four per cent between 1950-2000 – twice as fast as predicted by current climate models.

They conservatively estimate it could triple by the end of the century, leaving dry land masses like Australia struggling to meet their need for fresh water.

“We’re pretty sure that this is clear evidence it’s already happening, that the water cycle has accelerated and the rates at which it’s accelerating per degree of warming are probably higher than our current models project,” Dr Wijffels said.

“You can already see some of the small changes, some of the loss of rainfall that’s happened in some parts of Australia like the southwest, what a challenge that’s presented now to the water planning authorities around securing surface water supplies to feed the city of Perth.

“That loss is only a few per cent so, if we see a very large percentage change in how the water cycle functions, then it will be quite challenging.”

Australia would continue to experience the periodic El Nino and La Nina dry and wet spells, but the game would have very different rules.

“What we need to prepare for is an underlying, long-term change of the background,” Dr Wijffels said.

“El Nino and La Nina will continue to happen without a doubt, they’re going to be coming and going as they always have for thousands of years.

“Underneath that the base climate is going to be drifting … the dry areas are going to become even more water stressed and the wet regions will probably become wetter.”

The study is considered one of the most accurate of its type because data was collected from ocean monitoring equipment, including the Argo fleet of 3500 robotic floats deployed over the past decade.

Scientists have previously struggled to produce estimates of water cycle changes because land-based observations of rainfall and evaporation are sparse.