The wet gets wetter, the dry dryer, thanks to climate change

WET areas have become wetter and dry areas drier over the past 50 years due to global warming, a study of the saltiness of the world's oceans by a team including CSIRO researchers has shown.

The intensification of rainfall and evaporation patterns, which is occurring at twice the rate predicted by climate change models, could increase the incidence and severity of extreme weather events.

Team leader, Paul Durack, said the find was important because reductions in the availability of fresh water posed more of a risk to human societies and natural ecosystems than a rise in temperature alone.

''Changes to the global water cycle and the corresponding redistribution of rainfall will affect food availability, stability, access and utilisation,'' Dr Durack, a former CSIRO researcher now at the Lawrence Livermore National Laboratory in California, said.

The fact that hotter air can hold more water underpinned predictions that recent warming of the globe's surface and lower atmosphere could have already strengthened the natural evaporation and precipitation cycle - increasing rainfall where it was higher than average and decreasing it where it was lower.

Initial attempts to study this ''rich get richer'' effect, however, were hindered by a shortage of good rainfall records on land and a lack of long-term satellite measurements.

So Dr Durack studied the oceans. The results are published in Science.

They found that regions near the equator and the poles, where greater rainfall keeps surface waters less salty than average, had become even fresher in the past half century. Saltier areas in the centre of oceans where evaporation dominated, had become even saltier.